C++ Style Languages: C++, Objective-C, Java, C#

From Hyperpolyglot.org

a side-by-side reference sheet

	c++	objective c	java	c#
version used	g++ 4.6 with -std=c++0x flag	gcc 4.2	java 1.6	mono 2.10 (C# 4.0)
show version	$ g++ --version	$ gcc --version	$ javac -version	$ mcs --version
implicit prologue	#include <iostream> #include <string> using namespace std;
grammar and invocation
	c++	objective c	java	c#
hello world	$ cat hello.cpp #include <iostream> using namespace std; int main(int argc, char**arg) { cout << "Hello, World!" << endl; } $ g++ -std=c++0x hello.cpp $ ./a.out	$ cat hello.m #include <stdio.h> int main(int argc, char **argv) { printf("Hello, World!\n"); } $ gcc hello.m $ ./a.out	$ cat Hello.java public class Hello { public static void main(String[] args) { System.out.println("Hello, World!"); } } $ javac Hello.java $ java Hello	$ cat hello.cs using System; public class Hello { public static void Main() { Console.WriteLine("Hello, World!"); } } $ mcs hello.cs $ mono hello.exe
file suffixes source, header, object file	foo.cpp foo.h foo.o	Foo.m Foo.h Foo.o	Foo.java none Foo.class Foo.java must define a single top level class Foo	Foo.cs none Foo.exe or Foo.dll although files are often named after a class they contain, this is not required
block delimiters	{ }	{ }	{ }	{ }
statement terminator	;	;	;	;
top level statements	A source file will normally have #include directives at the top, followed by declarations, definitions, and namespaces containing declarations and definitions. After the preprocessor has finished processing a source file, the compilation unit will only contain declarations, definitions, and namespaces at the top level.		each file contains the following elements in order: (1) optional package directive (2) zero or more import directives (3) one public class definition and zero or more private class definitions
end-of-line comment	// comment	// comment	// comment	// comment
multiple line comment	/* comment another comment */	/* comment another comment */	/* comment another comment */	/* comment another comment */
variables and expressions
	c++	objective c	java	c#
local variable	int i; int j = 3; int k(7);	int i; int j = 3;	int i; int j = 3;	int i; int j = 3;
uninitialized local variable	The behavior is undefined. Most implementations do not zero-initialize stack variables, so the value will be whatever happened to be in memory.	behavior is undefined. Most implementations do not zero-initialize stack variables, so the value will be whatever happened to be in memory.	zero initialized	compiler prevents use of uninitialized local variable
global variable	// in foo.cpp and outside of any function // or class definition: int foo = 7; // in bar.cpp and outside of any function // or class definition: extern int foo;	in foo.cpp outside of any function or class definition: int foo = 7; in bar.cpp outside of any function or class definition: extern int foo;
constant	const int i = 7;	const int i = 7;	final int i = 7;	const int i = 7;
allocate heap	int* ip = new int;	#include <stdlib.h> int *ip = malloc(sizeof(int));	primitive types are always stack allocated. Use a wrapper class to store on the heap: Integer i = new Integer(0);	object i = 0;
free heap	delete i;	#include <stdlib.h> free(ip);	garbage collected	garbage collected
null	NULL	NULL	null	null
coalesce	string s1 = s2 \|\| "was null";	NSString *s1 = s2 \|\| @"was null";	String s1 = s2 == null ? "was null" : s2;	string s1 = s2 ?? "was null";
arithmetic and logic
	c++	objective c	java	c#
boolean type	bool	BOOL	boolean	bool
true and false	true false	YES NO	true false	true false
falsehoods	false 0 0.0 NULL	0 0.0 NULL	false	false
logical operators	&& \|\| ! and or not	&& \|\| !	&& \|\| !	&& \|\| !
relational operators	== != < > <= >=	== != < > <= >=	== != < > <= >=	== != < > <= >=
integer type	signed char n1; // 1+ bytes short int n2; // 2+ bytes int n3; // 2+ bytes long int n4; // 4+ bytes long long int n5; // 4+ bytes	signed char 1+ byte short int 2+ bytes int 2+ bytes long int 4+ bytes long long int 4+ bytes	byte 1 byte short 2 bytes int 4 bytes long 8 bytes	sbyte 1 byte short 2 bytes int 4 bytes long 8 bytes
unsigned type	unsigned char n1; // 1+ bytes unsigned short int n2; // 2+ bytes unsigned int n3; // 2+ bytes unsigned long int n4; // 4+ bytes unsigned long long int n5; // 4+ bytes	unsigned char: 8+ unsigned short int 2 bytes+ unsigned int 2 bytes+ unsigned long int 4+ bytes unsigned long long int 4+ bytes	char 2 bytes	byte 1 byte ushort 2 bytes uint 4 bytes ulong 8 bytes
float type	float x1; // 4 bytes double x2; // 8 bytes long double x3; // 16 bytes	float double long double	float 4 bytes double 8 bytes	float 4 bytes double 8 bytes
fixed type	none	none	none	decimal 12 bytes
arithmetic operators	+ - * / %	+ - * / %	+ - * / %	+ - * / %
integer division	// evaluates to 2: 7 / 3	evaluates to 2: 7 / 3	evaluates to 2: 7 / 3	evaluates to 2: 7 / 3
integer division by zero	process sent a SIGFPE signal	process sent a SIGFPE signal	throws java.lang.ArithmeticException	Syntax error if divisor is a constant. Otherwise throws System.DivideByZeroException
float division	7 / static_cast<float>(3)	7 / (float)3	7 / (float)3	7 / (float)3
float division by zero dividend is positive, zero, negative	inf nan -inf There are no portably defined literals or constants for the above values.	inf nan -inf there are no portably defined literals or constants for the above values.	Float.POSITIVE_INFINITY Float.NaN Float.NEGATIVE_INFINITY constants with same names defined in Double	float.PositiveInfinity float.NaN float.NegativeInfinity constants with same names defined in double
power	#include <math.h> double x = pow(2.0, 32.0);	#include <math.h> pow(2.0, 32.0);	Math.pow(2.0, 32.0);	System.Math.Pow(2.0, 32.0);
sqrt	#include <math.h> double x = sqrt(2);	#include <math.h> sqrt(2)	Math.sqrt(2)	Math.Sqrt(2)
sqrt -1	nan	nan	Double.NaN	double.NaN
transcendental functions	#include <math.h> exp log log2 log10 sin cos tan asin acos atan atan2	#include <math.h> exp log log2 log10 sin cos tan asin acos atan atan2	Math.exp Math.log none Math.log10 Math.sin Math.cos Math.tan Math.asin Math.acos Math.atan Math.atan2	using System; Math.Exp Math.Log none Math.Log10 Math.Sin Math.Cos Math.Tan Math.Asin Math.Acos Math.Atan Math.Atan2
transcendental constants	#include <math.h> double e = M_E; double pi = M_PI;	#include <math.h> M_E M_PI	Math.E Math.PI	System.Math.E System.Math.PI
float truncation towards zero, to nearest integer, towards -∞, towards ∞	#include <math.h> double x = 3.7; long trnc = static_cast<long>(x); long rnd = round(x); long flr = floorl(x); long cl = ceill(x);	#include <math.h> double d = 3.77; long trnc = (long)d; long rnd = round(d); long flr = floorl(d); long cl = ceill(d);	(long)3.77 Math.round(3.77) (long)Math.floor(3.77) (long)Math.ceil(3.77)	using System; (long)3.77 Math.Round(3.77) Math.Floor(3.77) Math.Ceiling(3.77)
absolute value	#include <stdlib.h> // abs() #include <math.h> // fabs() int n = -7; int absn = abs(n); double x = -7.77; double absx = fabs(x);	#include <stdlib.h> // abs() #include <math.h> // fabs() int i = -7; int ai = abs(i); float x = -7.77; float ax = fabs(x);	Math.abs(-7) Math.abs(-7.77)	System.Math.Abs(-7) System.Math.Abs(-7.77)
integer overflow	modular arithmetic The C standard does not define behavior for signed integers, however.	modular arithmetic The C standard does not define behavior for signed integers, however.	modular arithmetic	modular arithmetic
float overflow	no behavior defined by standard; many implementations return inf	no behavior defined by standard; many implementations return inf	Float.POSITIVE_INFINITY	float.PositiveInfinity
float limits largest finite float, smallest positive float	#include <float.h> FLT_MAX FLT_MIN DBL_MAX DBL_MIN LDBL_MAX LDBL_MIN		Float.MAX_VALUE Float.MIN_VALUE Double.MAX_VALUE Double.MIN_VALUE	float.MaxValue float.Epsilon double.MaxValue double.Epsilon
complex construction	#include <complex> complex<double> z(1.0, 2.0);
complex decomposition real and imaginary component, argument, absolute value, conjugate	z.real() z.imag() arg(z) abs(z) conj(z)
random number uniform integer, uniform float, normal float	#include <random> default_random_engine dre; uniform_int_distribution<int> uid(0, 99); uniform_real_distribution<double> urd(0.0, 1.0); normal_distribution<double> nd(0.0, 1.0); int i = uid(dre); double x = urd(dre); double y = nd(dre);	#include <stdlib.h> // assuming 100 much smaller than RAND_MAX: int i = rand() % 100; double x = drand48(); none	import java.util.Random; Random rnd = new Random(); int i = rnd.nextInt(100); double x = rnd.nextDouble(); double y = rnd.nextGaussian();	using System; Random rnd = new Random(); int i = rnd.Next(); double x = rnd.NextDouble(); none
random seed	#include <random> // set seed in constructor: default_random_engine dre(17); // set seed of existing engine: dre.seed(17);		import java.util.Random; Random rnd = new Random(); rnd.setSeed(17); seed can be passed to constructor	using System; Random rnd = new Random(17);
bit operators	<< >> & \| ^ ~ bitand bitor compl	<< >> & \| ^ ~	<< >> & \| ^ ~	<< >> & \| ^ ~
binary, octal, and hex literals	0b0101010 052 0x2a		none in Java 1.6 052 0x2a	none 052 0x2a
radix convert integer to and from string with radix			Integer.toString(42, 7) Integer.parseInt("60", 7)
strings
	c++	objective c	java	c#
string type	string s("lorem ipsum"); // convert to C string: const char* s2 = s.c_str();	NSString* s = @"lorem ipsum"; // convert to C string: const char* s2 = [s UTF8String];	java.lang.String	string
string literal	// const char*: "don't say \"no\""	@"don't say \"no""	"don't say\"no\""	"don't say \"no\""
newline in literal	Newlines in string literals are ignored.	string literals can extend over multiple lines, but the newlines do not appear in the resulting string	no	string literals can extend over multiple lines, but the newlines do not appear in the resulting string
literal escapes	\a \b \f \n \r \t \v \\ \" \' \xhh \o \oo \ooo	\a \b \f \n \r \t \v \\ \" \' \xhh \o \oo \ooo	\b \f \n \r \t \\ \" \' \uhhhh \o \oo \ooo	\a \b \f \n \r \t \v \\ \" \' \xhh \xhhhh \o \oo \ooo
allocate string	string* s = new string("hello");	NSString *s = @"hello";	String s = "hello"; String t = new String(s);	string s = "hello"; string t = string.Copy(s);
are strings mutable?	string s("bar"); s[2] = 'z';
copy string	string s("bar"); // use assignment or copy constructor: string s2 = s; string s3(s); // s contains "baz"; // s2 and s3 contain "bar": s[2] = 'z';
format string	#include <sstream> ostringstream oss; oss << "Spain: " << 7; string s(oss.str());	[NSString stringWithFormat:@"%@: %d", @"Spain", 7]	String.format("%s: %d", "Spain", 7)	string.Format("{0}: {1}", "Spain", 7)
compare strings	string s1("hello"); string s2("world"); // negative if s1 lexically before s2; // zero if s1 and s2 are equal: int result1 = s1.compare(s2); bool result2 = s1 == s2;	[@"hello" compare:@"hello"]	"hello".compareTo("world")	"hello".CompareTo("world")
concatenate and append	string s("hello"); string s2 = s + " world"; s += " world";	NSString s1 = @"hello"; NSString s2 = @" world"; NSString *s3 = [s1 stringByAppendingString:s2];	"hello" + " world"	"hello" + " world"
replicate	string hbar(80, '-');
translate case	#include <algorithm> string s("foo"); // in place: transform(s.begin(), s.end(), s.begin(), ::toupper); transform(s.begin(), s.end(), s.begin(), ::tolower); // non-destructive: string s2; s2.resize(s.size(); transform(s.begin(), s.end(), s2.begin(), ::toupper);	[@"HELLO" lowercaseString]	"hello".toUpperCase() "HELLO".toLowerCase()	"hello".ToUpper() HELLO".ToLower()
trim	#include <algorithm> string s(" hello "); // trim in place on left: s.erase( s.begin(), find_if( s.begin(), s.end(), not1(ptr_fun<int, int>(isspace)) ) ); // trim in place on right: s.erase( find_if( s.rbegin(), s.rend(), not1(ptr_fun<int, int>(isspace)) ).base(), s.end() );	[@" hello " stringByTrimmingCharactersInSet: [NSCharacterSet whitespaceCharacterSet]]	" hello ".trim()	" hello ".Trim()
pad on right, on left	#include <sstream> #include <iomanip> string s("hello"); string rpad(s); rpad += string(10 - s.length(), ' '); ostringstream oss; oss << setw(10) << s; string lpad(oss.str());	[@"hello" stringByPaddingToLength:10 withString:@" " startingAtIndex:0]
number to string			Integer.toString(14) Long.toString(14) Double.toString(14.7)	14.ToString() 14.7.ToString()
string to number	#include <sstream> stringstream ss("7 14.3 12"); int n1; double x; long n2; ss >> n1 >> x >> n2;	[@"14" integerValue] [@"14" longLongvalue] [@"14.7" floatValue] [@"14.7" doubleValue]	Byte.parseByte("14") Short.parseShort("14") Integer.parseInt("14") Long.parseLong("14") Float.parseFloat("14.7") Double.parseDouble("14.7")	byte.Parse("14") short.Parse("14") int.Parse("14") long.Parse("14") float.Parse("14") double.Parse("14") decimal.Parse("14")
join				System.String.Join(", ", names)
split	#include <boost/algorithm/string.hpp> #include <vector> string s("Bob Amy Ned"); vector<string> vec; boost::split(vec, s, boost::is_any_of(" "));	[@"Bob Ned Amy" componentsSeparatedByString:@" "]	"Bob Ned Amy".split(" ")	string[] names = "Bob Ned Amy".Split(' ');
serialize
string length	string s("hello"); size_t len = s.length();	[s length]	s.length()	s.Length
index of substring	string("hello").find("ll")	[@"hello" rangeOfString:@"ll"].location	"hello".indexOf("ll")	"hello".IndexOf("ll")
extract substring	string("hello").substr(2, 2)	[@"hello" substringWithRange:NSMakeRange(2, 2)]	"hello".substring(2,4)	"hello".Substring(2, 2)
character type	char wchar_t
character literal	char n = 'X';
test character letter, digit, whitespace, uppercase letter, lowercase letter	// functions have this signature: // // int (*)(int): // isalpha isdigit isspace isupper islower
regular expressions
	c++	objective c	java	c#
regex type	regex wregex
character class abbreviations	. \d \D \s \S \w \W
anchors	^ $ \b \B
lookahead positive, negative	(?=subpattern) (?!subpattern)
match test	#include <regex> regex rx(".ll."); bool match = regex_match("hello", rx);	NSPredicate pred = [NSPredicate predicateWithFormat:@"SELF MATCHES %@", @".ll.*"]; BOOL is_match = [pred evaluateWithObject:@"hello"];	boolean isMatch = "hello".matches(".ll.");	using System.Text.RegularExpressions; Regex regex = new Regex("ll"); bool isMatch = regex.IsMatch("hello");
case insensitive match test	#include <regex> regex rx("lorem", icase); bool match = regex_match("Lorem", rx);
modifiers
substitution			String s1 = "hello".replace("ll","LL"); String s2 = "hello".replaceAll("l","L");	using System.Text.RegularExpressions; Regex r1 = new Regex("ll"); String s1 = r1.Replace("hello", "LL", 1); Regex r2 = new Regex("l"); String s2 = r2.Replace("hello", "L");
match, prematch, postmatch
group capture
dates and time
	c++	objective c	java	c#
date and time type			java.util.Date	System.DateTime
current date and time			import java.util.Date; long millis = System.currentTimeMillis(); Date dt = new Date(millis);	DateTime dt = DateTime.Now();
to unix epoch, from unix epoch			long epoch = dt.getTime() / 1000; Date dt2 = new Date(epoch * 1000);	long hundredM = 100 * 1000 * 1000; long sec = dt.ToFileTimeUtc() / hundredM; long epoch = sec - 1164444480; long ft = (epoch + 1164444480) * hundredM; Date dt2 = DateTime.FromFiltTimeUtc(ft);
date and time to string			dt.toString()
format date			String s = "yyyy-MM-dd HH:mm:ss"; DateFormat fmt = new SimpleDateFormat(s); String s2 = fmt.format(dt);	String s = "yyyy-MM-dd HH:mm:ss"); String s2 = dt.ToString(s);
parse date			String s = "2011-05-03 17:00:00"; Date dt2 = fmt.parse(s);	CultureInfo enUS = new CultureInfo("en-US"); DateTime dt2 = DateTime.ParseExact( "2011-05-03 17:00:00", "yyyy-MM-dd HH:mm:ss", enUS);
date subtraction			difference in milliseconds as a long: dt2.getTime() - dt.getTime()
add duration			long day_ms = 24 * 3600 * 1000; Date dt = new Date(dt.getTime() + day_ms));
date parts
time parts
arrays
	c++	objective c	java	c#
allocate array on stack	int a[10];	int a[10];	arrays must be allocated on heap	arrays must be allocated on heap
allocate array on heap	int *a = new int[10];	#include <stdlib.h> int *a = calloc(10, sizeof(int));	int[] a = new int[10];	int[] a = new int[10];
free array on heap	delete[] a;	#include <stdlib.h> free(a);	garbage collected	garbage collected
array literal	int a[] = {1,2,3};	NSArray *a = [NSArray arrayWithObjects:@"hello", @"goodbye", nil];	int[] a = {1,2,3};	int[] a = {1,2,3};
array access	a[0]	[a objectAtIndex:0]	a[0]	a[0]
length	none	[a count]	a.length	a.Length
array out-of-bounds result	undefined, possible SIGSEGV	raises NSRangeException exception	ArrayIndexOutOfBoundsException	IndexOutOfRangeException
array iteration	int a[10]; for (i=0; i<10; i++ ) { do something with a[i] }	NSEnumerator i = [a objectEnumerator]; id o; while (o = [i nextObject]) { do something with o* }	for (String name : names) {	foreach (string name in names) {
vector declaration	#include <vector> vector <int> vec;	NSMutableArray *a = [NSMutableArray arrayWithCapacity:10];	java.util.Vector<String> vec = new java.util.Vector<String>();	using System.Collections.Generic; List<string> l = new List<string>();
vector push	vec.push_back(7);	[a addObject:@"hello"];	vec.add("hello"); or vec.add(vec.size(), "hello")	l.Add("hello");
vector pop	vec.pop_back();	[a removeLastObject];	vec.removeElementAt(vec.size()-1);	l.RemoveAt(l.Count - 1);
vector size	vec.size()	[a count]	vec.size()	l.Count
vector access	vec[0] vec.at(0)	[a objectAtIndex:0]	vec.elementAt(0)	l[0]
vector out of bounds result	vec[] has undefined behavior vec.at() raises out_of_range	raises NSRangeException	throws ArrayIndexOutOfBoundsException	throws System.ArgumentOutOfRangeException
vector iteration	int sum = 0; vector<int>::iterator vi; for (vi = vec.begin(); vi != vec.end(); vi++ ) { sum += *vi; }	NSEnumerator i = [a objectEnumerator]; id o; while (o = [i nextObject]) { do something with o* }	for ( String s : vec ) { do something with s }	foreach ( string s in l ) { do something with s }
dictionaries
	c++	objective c	java	c#
pair	pair<int, float> p(7, 3.14); cout << p.first << ", " << p.second << endl;			using System.Collections.Generic; KeyValuePair<string,int> pr = new KeyValuePair<string,int>("hello",5); System.Console.WriteLine("{0} {1}", pr.Key, pr.Value);
map declaration	#include <map> map<string, int> m;	NSMutableDictionary *dict = [NSMutableDictionary dictionaryWithCapacity:10];	java.util.TreeMap<String, Integer> m = new java.util.TreeMap<String, Integer>();	using System.Collections.Generic; Dictionary<string, int> dict = new Dictionary<string, int>();
map access	m["hello"] = 5; cout << m["hello"]) << endl;	[dict setObject:@"5" forKey:@"hello"]; [dict objectForKey:@"hello"]	m.put("hello", 5); m.get("hello")	dict.Add("hello", 5); dict["hello"]
map size	m.size()	[dict count]	m.size()	dict.Count
map remove element	m.erase(m.find("hello"));	[dict removeObjectForKey:@"hello"];	m.remove("hello");	dict.Remove("hello");
map element not found result	NULL	NULL	null	throws KeyNotFoundException in System.Collections.Generic
map iterate	map<string,int>::iterator mi; for (mi = m.begin(); mi != m.end(); mi++) { printf("%s %d", mi->first, mi->second) }	NSEnumerator i = [dict keyEnumerator]; id key; while ((key = [i nextObject])) { do something with key* }	for ( java.util.Map.Entry<String, Integer> e : m.entrySet() ) { use e.getKey() or e.getValue() }	foreach ( KeyValuePair<string,int> e in dict) { use e.Key and e.Value }
user-defined types
	c++	objective c	java	c#
typedef	typedef int customer_id; customer_id cid = 3;	typedef int customer_id; customer_id cid = 3;	none	none
enum	enum day_of_week { mon, tue, wed, thu, fri, sat, sun }; day_of_week d = tue;	enum day_of_week { mon, tue, wed, thu, fri, sat, sun }; enum day_of_week d = tue;	public enum DayOfWeek { MON, TUE, WED, THU, FRI, SAT, SUN }; DayOfWeek d = DayOfWeek.TUE;	public enum DayOfWeek { MON, TUE, WED, THU, FRI, SAT, SUN }; DayOfWeek d = DayOfWeek.TUE;
struct definition	class MedalCount { public: const char *country; int gold; int silver; int bronze; };	struct medal_count { const char* country; int gold; int silver; int bronze; };	public class MedalCount { public String country; public int gold; public int silver; public int bronze; }	public class MedalCount { public string country; public int gold; public int silver; public int bronze; }
struct declaration	MedalCount spain;	struct medal_count spain;	MedalCount spain = new MedalCount();	MedalCount spain = new MedalCount();
struct initialization	MedalCount spain = { "Spain", 3, 7, 4 };	struct medal_count spain = { "Spain", 3, 7, 4}; struct medal_count france = { .gold = 8, .silver = 7, .bronze = 9, .country = "France" };	no object literal syntax; define a constructor	no object literal syntax; define a constructor
struct member assignment	spain.country = "Spain"; spain.gold = 3; spain.silver = 7; spain.bronze = 4;	spain.country = "Spain"; spain.gold = 3; spain.silver = 7; spain.bronze = 4;	spain.country = "Spain"; spain.gold = 3; spain.silver = 7; spain.bronze = 4;	spain.country = "Spain"; spain.gold = 3; spain.silver = 7; spain.bronze = 4;
struct member access	int spain_total = spain.gold + spain.silver + spain.bronze;	int spain_total = spain.gold + spain.silver + spain.bronze;	int spain_total = spain.gold + spain.silver + spain.bronze;	int spain_total = spain.gold + spain.silver + spain.bronze;
functions
	c++	objective c	java	c#
pass by value	void use_integer(int i) { // function body } int i = 7; use_integer(i);	void use_integer(int i) { function body } int i = 7; use_integer(i);	primitive types are always passed by value	primitive types are always passed by value
pass by address	void use_iptr(int i) { function body* } int i = 7; use_iptr(&i);	void use_iptr(int i) { function body* } int i = 7; use_iptr(&i);	none	none
pass by reference	void use_iref(int& i) { printf("using iref: %d", i); } int i = 7; use_iref(i);	none	objects and arrays are always passed by reference	objects and arrays are always passed by reference
default argument value	float log(float exp, float base=10.0) {	none	use method overloading	use method overloading
named parameters	none	+(float)weight: (float) w height: (float) h { return (w * 703) / (h * h); } +(float)height: (float) h weight: (float) w { return [BMI weight: w height: h]; } [BMI weight:155 height:70]; [BMI height:70 weight:155];	none	added in C# 4.0: static int BMI(int weight, int height) { return (weight * 703) / (height * height); } BMI(weight: 123, height: 64); BMI(height: 64, weight: 123);
function overloading	yes	method overloading only	yes	yes
variable number of arguments	use C; use default values or function overloading for finite number of arities	use C; use method overloading for finite arities	public static String concat(String first, String… rest) { StringBuilder sb = new StringBuilder(first); for (String arg: rest) { sb.append(arg); } return sb.toString(); } String s = Concat.concat("Hello", ", ", "World", "!");	public static string concat(params string[] args) { return System.String.Join("",args); } string s = Concat.concat("Hello", ", ", "World", "!")
passing functions
anonymous function
operator overloading	Rational Rational::operator+(Rational& o) { return Rational(this->numo.denom + o.numthis->denom, this->denom * o.denom); }	none	none	public static Rational operator+(Rational a, Rational b) { return new Rational(a.numb.denom + b.num a.denom,a.denom*b.denom); }
execution control
	c++	objective c	java	c#
if	int signum; if (n > 0) { signum = 1; } else if (n == 0) { signum = 0; } else { signum = -1; }	if (i>0) { signum = 1; } else if (i==0) { signum = 0; } else { signum = -1; }	if (i>0) { signum = 1; } else if (i==0) { signum = 0; } else { signum = -1; }	if (i>0) { signum = 1; } else if (i==0) { signum = 0; } else { signum = -1; }
switch	const int INVALID_BINARY_DIGIT(-1); int bindigit; switch(n) { case 0: case 1: bindigit = n; break; default: bindigit = INVALID_BINARY_DIGIT; break; }	switch(i) { case 0: 0; break; case 1: 1; break; default: -1; break; }	switch(i) { case 0: 0; break; case 1: 1; break; default: -1; break; }	switch(i) { case 0: 0; break; case 1: 1; break; default: -1; break; }
while	int i(1), fact(1), n(10); while (i < n) { fact *= i; i++; }	int i = 0; while (i<10) { … i++; }	int i = 0; while (i<10) { … i++; }	int i = 0; while (i<10) { … i++; }
for	int i, fact, n(10); for (i = 1, fact = 1; i <= n; i++) { fact *= i; }	int i, n; for (i=1,n=1; i<=10; i++) { n *= i; }	int n = 1; for (int i=1; i<=10; i++) { n *= i; }	int i, n; for (i=1,n=1; i<=10; i++) { n *= i; }
throw exception	throw exception();	NSException *exc = [NSException exceptionWithName:@"error" reason:@"failed" userInfo:nil]; @throw exc;	throw new Exception("failed");	throw new System.Exception("failed");
catch exception	try { throw exception(); } catch (exception& e) { cout << "failed" << endl; }	@try { [NSException raise:@"error" format:@"failed"]; } @catch (NSException *e) { printf([[e reason] UTF8String]); }	try { throw new Exception("failed"); } catch (Exception e) { System.out.println(e.getMessage()); }	try { throw new System.Exception("failed"); } catch (System.Exception e) { System.Console.WriteLine(e.Message); }
finally clause	use local object with destructor	@try { risky code } @finally { perform cleanup }	try { risky code } finally { perform cleanup }	try { risky code } finally { perform cleanup }
methods must declare exceptions	no	no	yes	no
file handles
	c++	objective c	java	c#
standard file handles	cin cout cerr clog		System.in System.out System.err
printf	cout << "count: " << 7 << endl;	printf("count: %d\n", 7);	System.out.printf("count: %d", 7);	System.Console.WriteLine("count: {0}", 7);
read from file	#include <fstream> string line; ifstream f("/etc/passwd"); if (f.is_open()) { while (!f.eof()) { getline(f, line); process line } f.close(); if ( 0 != f.fail() ) { handle error } } else { handle error }	NSError error = nil; NSString s = [NSString stringWithContentsOfFile: @"/etc/passwd" encoding:NSUTF8StringEncoding error:&error]; if ( error != nil ) { handle error } NSArray a = [s componentsSeparatedByString:@"\n"]; id line; while (line = [i nextObject]) { process line* }	import java.io.BufferedReader; import java.io.FileReader; BufferedReader in = new BufferedReader(new FileReader("/etc/passwd")); String line; while ((line = in.readLine()) != null) { process line }	using System.IO; StreamReader sr = new StreamReader("/etc/passwd"); string line; while ((line = sr.ReadLine()) != null) { use line }
write to file	#include <fstream> ofstream f("/tmp/test4"); int i; for (i=0; i<10; i++) { f << i << endl; } f.close(); if (0 != f.fail()) { handle error }		import java.io.BufferedWriter; import java.io.FileWriter; BufferedWriter fout = new BufferedWriter(new FileWriter("/tmp/test2")); int i; for (i=0; i<10; i++) { fout.write(String.format("%d", i)); fout.newLine(); } fout.close();	using System.IO; StreamWriter fout = new StreamWriter("/tmp/test3"); int i; for (i=0; i<10; i++) { fout.WriteLine(i.ToString()); } fout.Close();
files
	c++	objective c	java	c#
file exists test, file regular test			import java.io.File; File f = new File("/etc/hosts"); f.exists() f.isFile()	System.IO.File.Exists("/etc/hosts")
file size			import java.io.File; File f = new File("/etc/hosts"); f.length()
is file readable, writable, executable			import java.io.File; File f = new File("/etc/hosts"); f.canRead() f.canWrite() f.canExecute()
set file permissions			import java.io.File; File f = new File("/tmp/foo"); // sets owner perms; to turn perms off // set arg to false: f.setReadable(true); f.setWritable(true); f.setExecutable(true); // if 2nd arg is false, perms are // for owner, group, and other: f.setReadable(true, false); f.setWritable(true, false); f.setExecutable(true, false);
copy file, remove file, rename file			import java.io.File; ?? File f2 = new File("/tmp/foo"); f2.delete(); File f3 = new File("/tmp/bar"); f3.renameTo(new File("/tmp/bar"));
directories
	c++	objective c	java	c#
build pathname			import java.io.File; File root = File.listRoots()[0]; File etc = new File(root, "etc"); File hosts = newFile(etc, "hosts"); String path = hosts.getPath();
dirname and basename	#include <libgen.h> string s1 = dirname("/etc/hosts"); string s2 = basename("/etc/hosts");		import java.io.File; File f = new File("/etc/hosts"); String dirname = f.getParent(); String basename = f.getName();
absolute pathname	#include <climits> #include <cstdlib> char buf[PATH_MAX]; if (realpath("..", buf) == NULL) { throw exception(); } else { string path(buf); }		import java.io.File; File f = new File("foo"); String abspath = f.getAbsolutePath(); // getCanonicalPath() expands .. and .: File f2 = new File("../foo"); String abspath2 = f2.getCanonicalPath(); File f3 = new File("./foo"); String abspath3 = f3.getCanonicalPath();
iterate over directory by file			import java.io.File; File dir = new File("/etc"); // iterate over names: for (String name: dir.list()) { System.out.println(name); } // iterate over file objects: for (File f: dir.listFiles()) { System.out.println(f.getName()); }
glob paths
make directory			import java.io.File; File f = new File("/tmp/foo/bar"); f.mkdirs();
recursive copy
remove empty directory
remove directory and contents
directory test			import java.io.File; File f = new File("/tmp"); f.isDirectory()
generate unused directory name
system temporary file directory
processes and environment
	c++	objective c	java	c#
signature of main	int main(int argc, char **argv) {	int main(int argc, char **argv) {	public class Foo { public static void main(String[] args) {	public class Foo { public static void Main(string[] args) {
first argument	pathname of executable	pathname of executable	first command line argument	first command line argument
environment variable	#include <stdlib.h> char *home = getenv("HOME"); setenv("EDITOR", "emacs", 1); unsetenv("EDITOR");	NSString *home = [[[NSProcessInfo processInfo] environment] objectForKey:@"HOME"];	String home = System.getenv("HOME");	using System.Environment; string home = GetEnvironmentVariable("HOME"); SetEnvironmentVariable("EDITOR", "emacs"); SetEnvironmentVariable("EDITOR", null);
iterate through environment variables		NSEnumerator i = [[[NSProcessInfo processInfo] environment] keyEnumerator]; id key; while ((key = [i nextObject])) { use NSString key* }	import java.util.Map; Map<String, String> env = System.getenv(); for (String name : env.keySet()) { String value = env.get(name)); }	using System.Collections; using System.Environment; IDictionary env = GetEnvironmentVariables(); foreach (DictionaryEntry de in env) { use de.Key or de.Value }
libraries and namespaces
	c++	objective c	java	c#
standard library name	C++ Standard Library	Foundation Framework	Java API	Base Class Library
declare namespace	namespace foo { namespace bar { class Baz { static const int ANSWER = 42; }; } }		package foo.bar; public class Baz { public static final int ANSWER = 42; }	namespace foo { namespace bar { public class Baz { public const int ANSWER = 42; }; } }
multiple namespaces per file	yes		no	yes
namespaces map to directories	no		yes	no
import namespace	using namespace foo::bar; cout << Baz::ANSWER << endl;		import foo.bar.*; System.out.println(Baz.ANSWER);	using foo.bar; System.Console.WriteLine(Baz.ANSWER);
import part of namespace	using namespace foo; cout << bar::Baz::ANSWER << endl;		none	none
import symbol	using foo::bar::Baz; cout << Baz::ANSWER << endl;		import foo.bar.Baz; System.out.println(Baz.ANSWER);	none
import static symbol	none		import static foo.bar.Baz.ANSWER; System.out.println(ANSWER);	none
import position	anywhere a statement is legal		after package and before type definitions	outside of class definitions
using a symbol that hasn't been imported	cout << foo::bar::Baz::ANSWER << endl;		System.out.println(foo.bar.Baz.ANSWER);	using System.Console; WriteLine(foo.bar.Baz.ANSWER);
application environment
multiple installations			set JAVA_HOME environment variable to directory containing a bin subdirectory with java, javac, and other command line tools. Put $JAVA_HOME/bin at front of search path.
package manager
objects
	c++	objective c	java	c#
semantics of ==	value comparison	object identity comparison	object identity comparison	value comparison
define class	Rational.hpp: class Rational { public: int num, denom; Rational(int num, int denom); virtual ~Rational(); Rational operator+(Rational& addend); static Rational max(Rational& a, Rational& b); };	Rational.h: #import <Foundation/Foundation.h> @interface Rational : NSObject { int num; int denom; } @property int num, denom; -(Rational) initWith: (int) n: (int) d; -(Rational) add: (Rational ) o; @end Rational.m:* #include "Rational.h" @implementation Rational @synthesize num, denom; -(Rational) add: (Rational) o { int sum_n = self.num * o.denom + o.num * self.denom; int sum_d = self.denom * o.denom; Rational* sum = [[Rational alloc] initWith: sum_n: sum_d]; return sum; } @end	public class Rational { public int num; public int denom; public Rational add(Rational o) throws Exception { return new Rational(this.numo.denom + o.numthis.denom,this.denomo.denom); } public static Rational max(Rational a, Rational b) { return (a.numb.denom > a.num*b.denom) ? a : b; } }	public class Rational { public int num; public int denom; }
class definition location	top level, class block, or function block	top level	top level, class block, or function block for anonymous classes
constructor	Rational::Rational(int n, int d) : num(n), denom(d) { if (denom == 0) { throw "zero denominator"; } int div = gcd(n,d); num = num / div; denom = denom / div; }	-(Rational*) initWith: (int) n: (int) d { self = [super init]; if (self) { self.num = n; self.denom = d; } return self; }	public Rational(int n, int d) throws Exception { if (d == 0) { throw new Exception("zero denominator"); } if ( d < 0 ) { this.num = -1 * n; this.denom = -1 * d; } else { this.num = n; this.denom = d; } }	public Rational(int n, int d) { if (0 == d) { throw new System.Exception("zero denominator"); } if (d < 0) { this.num = -1 * n; this.denom = -1 * d; } else { this.num = n; this.denom = d; } }
create object	Rational r1(7,3); Rational *r2 = new Rational(8,5);	Rational *r = [[Rational alloc] initWith: 7: 3];	Rational r = new Rational(7,3);	Rational r = new Rational(7,3);
destructor	Rational::~Rational() {};	-(void) dealloc { [super dealloc]; printf("deallocated…"); }	protected void finalize() throws Throwable { super.finalize(); }	~Rational() { perform cleanup }
destroy object	delete r2;	[r release];	none	none
define method	int Rational::height() { return (abs(num) > abs(denom)) ? abs(num) : abs(denom); }	-(int) height { if ( abs(self.num) > abs(self.denom) ) { return abs(self.num); } return abs(self.denom); }	public int height() { return (Math.abs(this.num) > this.denom) ? Math.abs(this.num) : this.denom; }	public int Height() { return (System.Math.Abs(this.num) > this.denom) ? System.Math.Abs(this.num) : this.denom; }
invoke method	r1.height(); r2->height();	[r1 height];	r.height();	r.Height();
dynamic dispatch	declare as virtual in base class	dispatch always dynamic	dispatch dynamic by default	declare as virtual in base class and override in derived class
static dispatch	dispatch static by default	dispatch always dynamic	declare as final, private, or static (i.e. make it a class method)	dispatch static by default; compiler error if same method defined in base and derived class and not marked virtual in base class
define class method	declare static in class definition	precede definition with +: +(Rational) max: (Rational) a: (Rational) b { if ( a.num b.denom > b.num * a.denom ) { return a; } return b; }	declare static in class definition	declare static in class definition
invoke class method
name of receiver	this	self	this	this
access control	access keywords define regions: class Foo { int privateInt1; int privateInt2; public: int publicInt1; int publicInt2; protected: int protectedInt1; int protectedInt2; private: int privateInt3; int privateInt4; };	access keywords define regions: @interface Foo : NSObject { int protectedInt1; int protectedInt2; @public int publicInt1; int publicInt2; @protected int protectedInt3; int protectedInt4; @private int privateInt1; int privateInt2; } @end	access keywords required for methods and members: public class Foo { private int privateInt; protected int protectedInt; public int publicInt; }	access keywords available for methods and members: public class Foo { private int privateInt1; int privateInt2; protected int protectedInt; public int publicInt; }
anonymous class	possible but not useful	none	(new Object() { public void hello() { System.out.println("hello!"); } }).hello();
subclass	class Integer : public Rational { public: Integer(int n); virtual ~Integer(); };		public class RInteger extends Rational { public RInteger(int n) throws Throwable { super(n, 1); } }
invoking superclass constructor	Integer::Integer(int n) : Rational(n, 1) { }		super(n, 1);
mark class underivable or method unoverrideable	none	none	final	sealed
root class	none	NSObject	java.lang.Object	System.Object
root class methods	none	autorelease class conformsToProtocol: hash isEqual: isKindOfClass: isProxy performSelector: performSelector:withObject: performSelector:withObject:withObject: release respondsToSelector: retain retainCount self superclass	clone() equals() finalize() getClass() hashCode() toString()	Equals() Finalize() GetHashCode() GetType() MemberwiseClone() ReferenceEquals() ToString()
generic types
	c++	objective c	java	c#
define generic type	template <class A> class Foo { public: A a; Foo(A a); }; template <class A> Foo<A>::Foo(A a) : a(a) { }		public class Foo<A> { public A a; public Foo(A a) { this.a = a; } }	public class Foo<A> { public A a; public Foo(A a) { this.a = a; } }
instantiate generic type	Foo<string> f = Foo<string>("foo");		Foo<String> f = new Foo<String>("foo");	Foo<string> f = new Foo<string>("foo");
generic function	template <class C> C add(C a, C b) { return a + b; }
generic array	template <class C> class Foo { public: C a[10]; };		not permitted. Use Object as the element type for the array or use an ArrayList.	public class Bar<C> { public C[] a; public Bar(C c) { this.a = new C[10]; } }
value parameter	template <int N> int add(int i) { return N+i; } cout << add<7>(3) << endl;
template parameter
template specialization
multiple type parameters	template <class A, class B> class Pair { public: A a; B b; Pair(A a, B b); }; template <class A, class B> Pair<A, B>::Pair(A a, B b) : a(a), b(b) { } Pair<int, string> p = Pair<int, string>(7, "foo");
generic type parameters	Pair<int, Foo<string> > p = Pair<int, Foo<string> >( 7, Foo<string>("foo"));
template parameters
reflection
	c++	objective c	java	c#
get type class of object			o = new Object(); Class c = o.getClass();	object o = new object(); System.Type t = o.GetType(); or System.type t = typeof(o);
get type class from string			Class c = Class.forName("java.io.File");	using System; Type t = Type.GetType("object");
get type class from type identifier	typeid(Foo)			System.Type t = typeof(object);
class name	typeid(Foo).name()		String name = c.getName();	t.ToString();
get methods			import java.lang.reflect.*; Method[] m = c.getMethods();	using System.Reflection; System.Type t = typeof(object); MethodInfo[] a = t.GetMethods();
has method			import java.lang.reflect.*; Class c = Class.forName("java.io.File"); Method[] a = c.getMethods(); boolean hasMethod = false; for (int i=0; i < a.length; i++) { if (a[i].getName() == "toString") { hasMethod = true; } }	null if method not found: MethodInfo m = t.GetMethod("ToString");
invoke method object			import java.lang.reflect.*; Class c = Class.forName("java.io.File"); Method m = c.getMethod("toString"); Object o = new Object(); m.invoke(o);	m.Invoke(o);
net and web
	c++	objective c	java	c#
url encode/decode			import java.net.URLEncoder; import java.net.URLDecoder; String url = "http://www.google.com"; String s = URLEncoder.encode(url, "utf8"); String s2 = URLDecoder.decode(s, "utf8");
unit tests
	c++	objective c	java	c#
test class	$ cat > test_foo.cpp #include <cppunit/TestCaller.h> #include <cppunit/TestCase.h> #include <cppunit/TestSuite.h> #include "test_foo.h" using namespace CppUnit; void TestFoo::test_01() { CPPUNIT_ASSERT_EQUAL(1, 1); } Test * TestFoo::suite() { TestSuite suiteOfTests = new TestSuite("Foo"); suiteOfTests->addTest( new TestCaller<TestFoo>( "test_01", &TestFoo::test_01)); return suiteOfTests; } $ cat > test_foo.h #include <cppunit/TestCase.h> class TestFoo: public CppUnit::TestCase { public: void test_01(); static CppUnit::Test suite(); };
run all tests	$ cat > test_runner.cpp #include <cppunit/ui/text/TestRunner.h> #include "test_foo.h" int main( int argc, char **argv) { CppUnit::TextUi::TestRunner runner; runner.addTest(TestFoo::suite()); runner.run(); return 0; } $ sudo apt-get install libcppunit-dev $ cat > Makefile test_runner: test_runner.o test_foo.o g++ -o $@ $^ -lcppunit check: test_runner ./test_runner $ make check
equality assertion	#include <cppunit/TestCase.h> CPPUNIT_ASSERT_EQUAL(1, 1); CPPUNIT_ASSERT_EQUAL("foo", "bar"); CPPUNIT_ASSERT_EQUAL_MESSAGE("1 != 1", 1, 1);
approximate assertion
exception assertion
setup
teardown
debugging and profiling
	c++	objective c	java	c#
debugger commands help, list source, (re)load executable, next, step, set breakpoint, show breakpoints, delete breakpoint, continue, backtrace, up stack, down stack, print, run, quit	> h > l [FIRST_LINENO, LAST_LINENO] > file PATH > n > s > b [FILE:]LINENO > i > d NUM > c > bt > up > do > p EXPR > r [ARG1[, [ARG2 ...]] > q
	_______________________________________________	_______________________________________________	_______________________________________________	_______________________________________________

version used

The compiler version used for this sheet.

implicit prologue

Code which examples in the sheet assume to have already been executed.

Grammar and Invocation

hello world

How to write, compile, and run a "Hello, World!" program.

file suffixes

For source files, header files, and compiled object files.

c++

The gcc compiler will treat a file with any of the following suffixes as C++ source:

 .cc .cp .cxx .cpp .CPP .c++ .C

GNU make has built-in rules which treat the following suffixes as C++ source:

.cc .C .cpp

block delimiters

How blocks are delimited.

A block contains a sequence of statements. Blocks for function bodies in function definitions; to define the branches of if statements and the bodies of while loops.

Class definition bodies are blocks, though the statements that appear in them are restricted to declarations and definitions.

Bare blocks can be used to limit the scope of variables which are declared inside them.

top level statements

Statements that can appear at the top level of a source file.

end-of-line comment

The syntax for a comment which is terminated by the end of the line.

multiple line comment

The syntax for a comment which can span multiple lines.

The /* */ delimiters do not nest. Using them to comment out code which already contains a /* */ comment usually results in a syntax error.

Variables and Expressions

local variable

How to declare a variable which is allocated on the stack.

uninitialized local variable

The value contained by a local variable that wasn't initialized.

allocate heap

How to allocate memory for a primitive type on the heap.

c++

new and delete can be used to manage the memory of both primitive types and objects.

objective c

Object C has a different memory management schemes for primitive types and objects. Objects are allocated with alloc and freed by means of NSAutoreleasePool. For primitive types the same techniques are used as for C. However, idiomatic Objective C will declare primitive types as local variables or as part of the state of an object and avoid explicit calls to malloc.

Arrays of objects can be created with NSArray and NSMutableArray.

java

In Java, arrays are always stored on the heap and the JVM is responsible for garbage collection. The primitive types are stored (1) on the local frame, (2) as part of the state of an object, or (3) as part of the state of a class. The primitive types are never stored in the heap directly and when they are part of object state they are garbage collected with the object. Primitive types are passed by value unless they are encapsulated in an object.

Each of the primitive types has a wrapper class, and instantiating this class is the best approximation in Java to allocating the primitive type on the heap:

Integer i = new Integer(0);

The compiler may instantiate the wrapper class implicitly; this is called boxing. The compiler also permits use of a wrapper class in the place of the primitive type, or unboxing.

C# behavior is like Java. Note that C# lacks specific wrapper classes for each primitive data type.

free heap

How to free the memory for a primitive type that was allocated on the heap.

null

C++

A typical definition:

const int NULL = 0;

coalesce

The equivalent of the COALESCE function from SQL.

C++, Objective C++:

The short circuit or operator || can be used as a coalesce operator. However, in C++ and Objective C, NULL is identical to zero, whereas in databases they are two distinct values.

Java:

The ternary operator provides the closest approximation to COALESCE, but it does not have the same behavior if the tested value has a side effect.

Arithmetic and Logic

boolean type

The following definitions are common:

typedef int BOOL;
#define TRUE 1
#define FALSE 0

Objective C

From objc.h:

typedef signed char BOOL;
#define YES (BOOL)1
#define NO (BOOL)0

bool is an alias for System.Boolean

true and false

Literals for the boolean values true and false.

The following definitions are common:

typedef int BOOL;
#define TRUE 1
#define FALSE 0

Objective C

From objc.h:

typedef signed char BOOL;
#define YES (BOOL)1
#define NO (BOOL)0

falsehoods

Values which evaluate as false in the conditional expression of an if statement.

logical operators

The logical operators.

In all languages on this sheet the && and || operators short circuit: i.e. && will not evaluate the 2nd argument if the 1st argument is false, and || will not evaluate the 2nd argument if the 1st argument is true. If the 2nd argument is not evaluated, side-effects that it contains are not executed.

C++

C++ defines and, or, and not to be synonyms of &&, ||, and !, with the same semantics and precedence.

Java

The arguments of the logical operators must be of type boolean.

The arguments of the logical operators must be of type bool.

relational operators

Binary operators which return boolean values.

integer type

Signed integer types.

C++

Whether char is a signed or unsigned type depends on the implementation.

C# has the following aliases:

sbyte: System.SByte
short: System.Int16
int: System.Int32
long: System.Int64

unsigned type

Unsigned integer types.

C++

Whether char is a signed or unsigned type depends on the implementation.

C# has the following aliases:

byte: System.Byte
ushort: System.UInt16
uint: System.UInt32
ulong: System.UInt64

float type

Floating point types.

C# has the following aliases:

float: System.Single
double: System.Double

fixed type

Fixed-point decimal types.

C#:

C# has the following alias:

decimal: System.Decimal

arithmetic operators

The arithmetic binary operators: addition, subtraction, multiplication, division, modulus.

integer division

How to get the quotient of two integers.

integer division by zero

The results of integer division by zero.

C++, Objective C

The behavior for division by zero is system dependent; the behavior described is nearly universal on Unix.

It is a compilation error to divide by a zero constant. Division by a variable set to zero results in a runtime exception.

float division

How to perform floating point division on two integers.

float division by zero

The result of floating point division by zero.

Modern hardware, if it implements floating point instructions, will implement instructions which conform to the IEEE 754 standard. The standard requires values for positive infinity, negative infinity, and not-a-number (NaN).

The C and C++ standards do not assume that they are running on hardware which provides these values; code which assumes they exist is not strictly speaking portable.

power

How to perform exponentiation.

C++

powm1 is an abbreviation for "power minus one". Hence the need to add one to get the answer.

sqrt

The positive square root function.

sqrt -1

The result of taking the square root of a negative number.

Here is a list of the standard mathematical functions whose domains do not cover the entire real number line:

function	returns inf on	returns nan on	returns -inf on
sqrt	inf	[-inf, 0)
log	inf	[-inf, 0)	0
asin		[-inf, -1) U (1, inf]
acos		[-inf, -1) U (1, inf]

transcendental functions

The exponential and logarithm functions; the trigonometric functions; the inverse trigonometric functions.

The arguments of the trigonometric functions are in radians as are the return values of the inverse trigonometric functions.

transcendental constants

The transcendental constants e and pi.

float truncation

Functions for converting a float to a nearby integer value.

The math.h library also provides floor and ceil which return double values.

Java:

Math.floor and Math.ceil return double values.

absolute value

The absolute value of a numeric quantity.

integer overflow

What happens when an integer expression results in a value larger than what can be stored in the integer type.

float overflow

What happens when a float expression results in a value larger than largest representable finite float value.

float limits

The largest finite floating point number and the smallest positive floating point number.

complex construction

How to construct a complex number.

complex decomposition

How to get the components of a complex number. Both Cartesian and polar decompositions are illustrated. Also how to get the complex conjugate.

random number

Ways to generate random numbers. The distributions are a uniform integer from 0 to 99; a uniform float from 0.0 to 1.0; a standard normal float.

c++:

The standard library includes functions for generating random numbers from other distributions.

random seed

How to set the seed for the random number generator.

bit operators

The bit operators: left shift, right shift, and, or, xor, and complement.

C++

bitand, bitor, and compl are synonyms of &, |, and ~ with identical precedence and semantics.

binary, octal, and hex literals

Binary, octal, and hex integer literals.

radix

How to convert integers to strings of digits of a given base. How to convert such strings into integers.

Strings

string type

The type for strings.

string literal

The syntax for string literals.

newline in literal

Can a newline be used in a string literal? Does the newline appear in the resulting string object?

literal escapes

Escape sequences that can be used in string literals.

allocate string

How to allocate a string.

Java

The following code

String t = new String(s);

creates a copy of the string s. However, because Java strings are immutable, it would be safe to store the same string object it t as follows:

String t = s;

are strings mutable?

copy string

format string

compare strings

C++

string::compare returns a positive value, 0, or a negative value depending upon whether the receiver is lexicographically greater, equal, or less than the argument. C++ overload the comparison operators (<, >, ==, !=, <=, >=) so that they can be used for string comparison.

Objective C
compare will return -1, 0, or 1.

Java

compareTo will return a negative value, 0, or a positive value.

CompareTo will return -1, 0, or 1.

concatenate

replicate

translate case

trim

pad

number to string

string to number

C++

strtoimax, strtol, strtoll, strtoumax, strtoul, and strtoull take three arguments:

intmax_t
strtoimax(const char *str, char **endp, int base);

The 2nd argument, if not NULL, will be set to first character in the string that is not part of the number. The 3rd argument can specify a base between 2 and 36.

strtof, strtod, and strtold take three arguments:

double
strtod(const char *str, char **endp);

Java

parseInt has an optional second argument for the base.

join

java:

Use StringBuilder to implement join:

public static String join(String[] a, String sep) {

    StringBuilder sb = new StringBuilder();

    for (int i=0; i<a.length; i++) {
        if (i > 0) {
            sb.append(sep);
        }
        sb.append(a[i]);
    }

    return sb.toString();
}

split

serialize

string length

index of substring

extract substring

character type

character literal

test character

Regular Expressions

regex match

regex substitute

Date and Time

date and time type

The data type used to store a combined date and time.

current date and time

How to get the current date and time.

to unix epoch, from unix epoch

How to convert a date/time object to the Unix epoch. How to convert the Unix epoch to a date/time object.

The Unix epoch is the number of seconds since 1 January 1970 UTC.

c#:

Windows file time is the number of nanoseconds since 1 January 1601 UTC divided by 100. The concept was introduced when journaling was added to NTFS with Windows 2000.

The magic constant (1164444480) used for the conversion can be calculated with the following code:

using System;
using System.Globalization;

CultureInfo enUS = new CultureInfo("en-US");
DateTime startEpoch = DateTime.ParseExact("1970-01-01 00:00:00 -00", "yyyy-MM-dd HH:mm:ss zz", enUS);

Console.WriteLine(startEpoch.ToFileTimeUtc() / (100*1000*1000));

format date

How to use a format string to display a date/time object.

The canonical example of doing this is the strftime function from the C standard library which defines used letters prefix by percent signs as conversion specification characters, e.g. %Y-%m-%d.

parse date

How to use a format string to parse date data from a string.

date subtraction

add duration

date parts

time parts

Arrays

allocate array on stack

How to allocate an array on the stack.

allocate array on heap

How to allocate an array on the heap.

free array on heap

How to free an array that was allocated on the heap.

array literal

Objective C

NSArray can only store instances of NSObject. For primitive types, use C arrays.

Java

Java permits arrays to be declared with C-style syntax:

int a[] = {1,2,3}

array element access

Arrays can be manipulated with pointer syntax. The following sets x and y to the same value:

int a[] = {3,7,4,8,5,9,6,10};
int x = a[4];
int y = *(a+4);

array out-of-bounds result

array iteration

C arrays do not store their size, so C developers normally store this information in a separate variable. Another option is to use a special value to mark the end of the array:

char *a[] = { "Bob", "Ned", "Amy", NULL };
int i;
for (i=0; a[i]; i++) {
  printf("%s\n", a[i]);
}

vector declaration

vector push

vector pop

vector size

vector access

vector out of bounds

vector iteration

Dictionaries

pair

map declaration

For those interested in an industrial strength hashtable implementation for C, here is the header file and the source file for the hashtable used by Ruby.
For those interested in a "Computer Science 101" implementation of a hashtable, here is a simpler source file and header file.

map access

map size

map remove

map element not found result

map iterator

User-Defined Types

typedef

Because C integer types don't have well defined sizes, typedef is sometimes employed to as an aid to writing portable code. One might include the following in a header file:

typedef int int32_t;

The rest of the code would declare integers that need to be 32 bits in size using int32_t and if the code needed to be ported to a platform with a 16 bit int, only a single place in the code requires change. In practice the typedef abstraction is leaky because functions in the standard library such as atoi, strtol, or the format strings used by printf depend on the underlying type used.

Java

Java has well defined integer sizes so typedef is not needed as a portability aid. In other situations where a C programmer would use a typedef for data abstraction, a Java programmer must either define a class or retain the raw primitive type throughout the code.

enum

Enums were added to the C standard when the language was standardized by ANSI in 1989.

An enum defines a family of integer constants. If an integer value is not explicitly provided for a constant, it is given a value one greater than the previous constant in the list. If the first constant in the list is not given an explicit value, it is assigned a value of zero. it is possible for constants in a list to share values. For example, in the following enum, a and c are both zero and b and d are both one.

enum { a=0, b, c=0, d };

A typedef can be used to make the enum keyword unnecessary in variable declarations:

typedef enum { mon, tue, wed, thu, fri, sat, sun } day_of_week;
day_of_week d = tue;

From the point of view of the C compiler, an enum is an int. The C compiler does not prevent assigning values to an enum type that are not in the enumerated list. Thus, the following code compiles:

enum day_of_week { mon, tue, wed, thu, fri, sat, sun };
day_of_week d = 10;

typedef enum { mon, tue, wed, thu, fri, sat, sun } day_of_week2;
day_of_week2 d2 = 10;

C++

C++ enums are more strongly typed the C enums. The compiler rejects attempts to assign a value to an enum variable that is not in the enumerated list. The following code:

enum day_of_week { mon, tue, wed, thu, fri, sat, sun };
day_of_week d = 10;

produces an error like the following:

main.cpp: In function ‘int main()’:
main.cpp:21: error: invalid conversion from ‘int’ to ‘main()::day_of_week’

Java

Java added enums in 1.5.

Java enums are strongly typed like C++ enums. Unlike C++ enums, it is an error to use an enum value in an integer context. The value has a method ordinal() which returns the integer value, however.

When used in a string context, an enum will evaluate as the string corresponding to its identifier: i.e. "TUE" for DayOfWeek.TUE. This string can be accessed explicitly with DayOfWeek.TUE.toString(). Conversely, DayOfWeek.valueOf("TUE") returns DayofWeek.TUE.

Java enums are subclasses of java.lang.Enum. In particular, an enum is a class, and if the last value if the enum definition is followed by a semicolon, what follows is a class body which can contain methods and constructors. An enum class is final and cannot be subclassed, but an enum can implement an interface.

Like Java enums, C# enums will return the string corresponding to their identifier. Unlike Java enums, C# enums will evaluate as integers in a numeric context.

When used as an argument in a C# style format string, an enum value returns the string corresponding to its identifier.

struct definition

A struct provides names for elements in a predefined set of data and permits the data to be accessed directly without the intermediation of getters and setters. C++, Java, and C# classes can be used to define structs by making the data members public. However, public data members violates the uniform access principle.

C++:

From The C++ Programming Language: 3rd Edition:

by definition, a struct is a class in which members are by default public; that is,

    struct s { ...

is simply shorthand for

    class s { public: ...

struct declaration

struct initialization

The literal format for a struct can only be used during initialization. If the member names are not provided, the values must occur in the order used in the definition.

struct member assignment

struct member access

The period operator used for member access has higher precedence than the pointer operator. Thus parens must be used
to get at the member of a struct referenced by a pointer:

struct medal_count {
char* country;
int gold;
int silver;
int bronze;
}

struct medal_count spain = { "Spain", 3, 7 4 };
struct medal_count *winner = &spain;
printf("The winner is %s with %d gold medals", (*winner).country, (*winner).gold);

ptr->mem is a shortcut for (*ptr).mem:

printf("The winner (%s) earned %d silver medals", winner->country, winner->silver);

Functions

pass by value

pass by address

pass by reference

default argument value

named parameters

objective C:

Named parameters must be invoked in the order in which they are defined in the method signature.

C#:

Named parameter do not need to be invoked in the order in which they are defined in the method signature. Additionally, their use in
invocation is optional: the arguments can be provided without names in which case the definition order must be used.

function overloading

variable number of arguments

The stdarg.h library supports variable length functions, but provides no means for the callee to determine how many arguments were provided. Two techniques for communicating the number of arguments to the caller are (1) devote one of the non-variable arguments for the purpose as illustrated in the table above, or (2) set the last argument to a sentinel value as illustrated below. Both techniques permit the caller to make a mistake that can cause the program to segfault. printf uses
the first technique, because it infers the number of arguments from the number of format specifiers in the format string.

char* concat(char* first,  ...) {
  int len;
  va_list ap;
  char *retval, *arg;
  va_start(ap, first);
  len = strlen(first);
  while (1) {
    arg = va_arg(ap, char*);
    if (!arg) {
      break;
    }
    len += strlen(arg);
  }
  va_end(ap);
  retval = calloc(len+1,sizeof(char));
  va_start(ap, first);
  strcpy(retval, first);
  len = strlen(first);
  while (1) {
    arg = va_arg(ap, char*);
    if (!arg) {
      break;
    }
    printf("copying %s\n", arg);
    strcpy(retval+len, arg);
    len += strlen(arg);
  }
  va_end(ap);
  return retval;
}

An example of use:

string *s = concat("Hello", ", ", "World", "!", NULL);

passing functions

anonymous function

operator overloading

Execution Control

for

if

For all five languages, the curly braces surrounding an if or else clause are optional if the clause contains a single statement. All five languages resolve resulting dangling else ambiguity by setting the value of c to 2 in the following code:

int a = 1;
int b = -1;
int c = 0;
if (a > 0)
if (b > 0)
  c=1;
else
  c= 2;

while

If the body of a while loop consists of a single statement the curly braces are optional:

int i = 0;
while (i<10)
  printf("%d\n", ++i);

switch

A switch statement branches based on the value of an integer or an integer expression. Each clause must be terminated by a break statement or execution will continue into the following clause.

throw exception

C++

C++ code can throw or catch any type of object or primitive data type. The C++ standard library throws subclasses of std::exception, which does not have a message member.

Objective C

Objective C can only throw an instance of NSException or one of its subclasses.

Java

Java can only throw an implementation of java.lang.Throwable.

C# can only throw an instance of System.Exception of one of its subclasses.

catch exception

C++

Exceptions can be caught by value or by reference. If the exception is an object and it is caught by value, the copy constructor and the destructor will be invoked.

Objective C

Exceptions are thrown and caught by pointer value.

finally clause

C++

Class Finally {

  void (*finally)();

  Finally(void (*f)()) : finally(f) {

  }

  ~Finally() {
    do_cleanup();
  }
};

{
  Cleanup c();

  risky();
}

methods must declare exceptions

Java

If a method throws a subclass of java.lang.Exception, it must declare the exception in its throws clause. This includes exceptions originating in code called by the method. On the other hand, if the method throws a subclass of java.lang.Error, no declaration in the throws clause is necessary.

File Handles

printf

How to print a formatted string to standard out.

read from file

If there is an error, the global variable errno will be set to a nonzero value, and strerror(errno) will return an error message for the error.

write to file

Files

Directories

Processes and Environment

signature of main

first argument

The first argument is the pathname to the executable. Whether the pathname is absolute or relative depends on how the executable was invoked. If the executable was invoked via a symlink, then the first argument is the pathname of the symlink, not the executable the symlink points to.

environment variable

iterate through environment variables

Library and Namespaces

standard library name

The name of the standard library.

C++

Standard Template Library (STL)

The STL might not be installed by default.

Objective C

Foundation Framework

The Foundation Framework is the core of Cocoa, a set of libraries for Objective C development on Mac OS X and the iPhone. The Foundation Framework descends from NextStep, hence the NS prefix in the class names. NextStep was made available to operating systems other than Next as OpenStep and the GNU implementation is called GNUStep.

Java

Java 1.6 API

.NET Framework 4 Class Library
Mono Documentation

The core of the .NET framework is called the Base Class Library. Mono implements the BCL, but not all of the .NET framework.

Objects

define class

constructor

create object

destructor

C++

The C++ compiler will normally see to it that the destructor for a class and all its superclasses is called. The compiler may not be aware of the true class of the object if it was upcast to one of its base class. If the destructor was not declared virtual, then the derived class destructor and any other base class constructors will not get called. Thus many developers declare all destructors virtual.

Java

Java does not chain finalize() methods, so the derived class should explicitly call the parent.

destroy object

Java

finalize() is called by the Java garbage collector.

define method

invoke method

dynamic dispatch

static dispatch

Method dispatch is static if the method is determined by the variable type, and dynamic if it is determined by the value type. These techniques of method dispatch yield different results when both the base class and the derived class have implementations for a method, and an instance of the derived class is being stored in a variable with type of the base class.

When dispatch is static, the compiler can determine the code that will be executed for the method call. When dispatch is dynamic, the code that will be executed is a runtime decision. C++ implementations usually achieve this by storing function pointers in the object: qv virtual method table.

The use of the keyword static in the declaration of a class method in C++, Java, and C# is perhaps unfortunate. Class methods are always statically dispatched, so the concepts are not unrelated.

define class method

invoke class method

name of receiver

access control

objective c:

Access control only applies to members; all methods are public. gcc 4.0 does not enforce the access restrictions; it merely gives warnings.

anonymous class

subclass

superclass constructor

mark class underivable or method overrideable

root class

Name of the root class, if there is one.

objective c:

It is possible to define a root class other than NSObject.

root class methods

A selection of methods available on the root class.

Generic Types

define generic type

instantiate generic type

Reflection

get type class of object

get type class from string

get type class from type identifier

c++:

typeid returns a value of type type_info. The assignment method and copy constructor of type_info are private.

class name

*c++:**

The string returned by type_info.name() contains more than the class name. The code below displayed the string "Z4mainE3Foo" when run on my system.

class Foo {
  int i;
};
puts(typeid(Foo).name());

get methods

has method

invoke method object

Net and Web

url encode/decode

How to URL encode and URL decode a string.

URL encoding is also called percent encoding. It is used to escape special characters in GET query string parameters.

Reserved characters according to RFC 3986 are replaced by a percent sign % followed by a two hex digit representation of the ASCII code. The reserved characters are: