C++简易
一.内存
1、栈区(stack):由编译器自动分配释放,存放函数的参数值,局部变量的值等。其操作方式类似于数据结构中的栈。
2、堆区(heap):动态内存分配例如malloc,一般由程序员分配释放, 若程序员不释放,程序结束时可能由OS回收 。注意它与数据结构中的堆是两回事,分配方式类似于链表。
3、全局区(静态区,static):全局变量和静态变量的存储是放在一块的,初始化的全局变量和静态变量在一块区域, 未初始化的全局变量和未初始化的静态变量在相邻的另一块区域。 - 程序结束后有系统释放
4、文字常量区:常量字符串就是放在这里的。 程序结束后由系统释放
5、程序代码区:存放函数体的二进制代码。
二.命名空间
防止命名冲突
1 #include<iostream> 2 using namespace std; 3 4 namespace mfc 5 { 6 int inflag; 7 void g(int a){cout << a << endl;} 8 } 9 10 namespace owl 11 { 12 int inflag; 13 void g(int b){cout << b << endl;} 14 } 15 16 int main() 17 { 18 mfc::inflag = 1; 19 owl::inflag = 2; 20 cout << mfc::inflag << endl;//1 21 cout << owl::inflag << endl;//2 22 23 mfc::g(1);//1 24 owl::g(2);//2 25 26 return 0; 27 }
1 #include<iostream> 2 using namespace std; 3 4 namespace mfc 5 { 6 int inflag; 7 void g(int a){cout << a << endl;} 8 } 9 10 namespace owl 11 { 12 int inflag; 13 void g(int b){cout << b << endl;} 14 } 15 using mfc::inflag; 16 int main() 17 { 18 inflag = 1; 19 owl::inflag = 2; 20 cout << inflag << endl;//1 21 cout << owl::inflag << endl;//2 22 return 0; 23 }
1 #include<iostream> 2 using namespace std; 3 4 namespace mfc 5 { 6 int inflag; 7 void g(int a){cout << a << endl;} 8 } 9 10 namespace owl 11 { 12 int inflag; 13 void g(int b){cout << b << endl;} 14 } 15 using namespace mfc; 16 17 int main() 18 { 19 inflag = 1; 20 owl::inflag = 2; 21 cout << inflag << endl;//1 22 cout << owl::inflag << endl;//2 23 g(1);//1 24 return 0; 25 }
三.操作符
1 #include<iostream> 2 #include <string> 3 #include <iomanip>//操作符 4 using namespace std; 5 6 int main() 7 { 8 double a = 3.1415; 9 double b = 2.2222; 10 string str; 11 12 //cout << right右对齐,cout << left左对齐,默认右对齐 13 cout << setw(8) << a << endl;//空格空格3.1415,设置字段位数 14 cout << setfill('c') << setw(8) << a << endl;//cc3.1415,填充字符 15 cout << setw(8) << a << endl;//cc3.1415 16 cout << setprecision(2) << a << endl;//3.1,设置字段精度 17 cout << setprecision(2) << fixed << a << endl;//3.14,小数点后精度 18 cout << showpoint << 2.2 << endl;//2.20,强制显示小数点及尾部0,可以用noshowpoint取消 19 cout << scientific << 33.33 << endl;//3.33e+001 20 21 cout << hex << 16 << endl; // 10 22 cout << oct << 8 << endl; // 10 23 cout << dec << 0x10 << endl; // 16 24 25 return 0; 26 }
四.文件
1 #include<iostream> 2 #include<fstream> 3 using namespace std; 4 5 int main() 6 { 7 ifstream infile; 8 ofstream outfile; 9 10 int num; 11 infile.open("E:\\1.txt"); 12 outfile.open("E:\\2.txt", ios::app); 13 /* 14 ios::out输出到文件删除原有内容 15 ios::binary以二进制格式打开文件 16 ios::app输出到文件保留原有内容 17 */ 18 19 if (! infile)//测试文件是否成功打开 20 { 21 cerr << "Error" << endl; 22 } 23 while (infile >> num) 24 { 25 cout << num << endl; 26 outfile << "Num = " << num << endl; 27 /* 28 Num = 1 29 Num = 2 30 Num = 3 31 Num = 4 32 Num = 5 33 */ 34 } 35 36 infile.close(); 37 outfile.close(); 38 39 40 return 0; 41 }
1 #include<iostream> 2 #include<fstream> 3 using namespace std; 4 5 int main() 6 { 7 ifstream infile; 8 ofstream outfile; 9 10 int num; 11 infile.open("E:\\1.txt"); 12 outfile.open("E:\\2.txt", ios::app); 13 /* 14 ios::out输出到文件删除原有内容 15 ios::binary以二进制格式打开文件 16 ios::app输出到文件保留原有内容 17 */ 18 19 if (!infile)//测试文件是否成功打开 20 { 21 cerr << "Error" << endl; 22 } 23 while (infile >> num) 24 { 25 cout << num << endl; 26 outfile << "Num = " << num << endl; 27 /* 28 Num = 1 29 Num = 2 30 Num = 3 31 Num = 4 32 Num = 5 33 */ 34 } 35 36 long location = outfile.tellp();//当前指针 37 location = 10L; 38 outfile.seekp(location);//移动到第十个字节处 39 location = outfile.tellp();//10 40 outfile.seekp(location, ios::beg);//从头数,移动到第十个字节处 41 location = outfile.tellp();//10 42 outfile.seekp(location, ios::cur);//从当前,移动到第十个字节处 43 location = outfile.tellp();//20 44 outfile.seekp(5L, ios::end);//从尾数,移动到第十个字节处 45 location = outfile.tellp();//5 46 47 48 location = infile.tellg();//当前指针 49 location = 10L; 50 infile.seekg(location);//移动到第十个字节处 51 location = infile.tellg();//-1 52 infile.seekg(location, ios::beg);//从头数,移动到第十个字节处 53 location = infile.tellg();//-1 54 infile.seekg(location, ios::cur);//从当前,移动到第十个字节处 55 location = infile.tellg();//-1 56 infile.seekg(5L, ios::end);//从尾数,移动到第十个字节处 57 location = infile.tellg();//-1 58 59 infile.close(); 60 outfile.close(); 61 62 63 return 0; 64 }
1 #include<iostream> 2 #include<fstream> 3 using namespace std; 4 5 class Student 6 { 7 public: 8 char name[500], score[500]; 9 }; 10 11 int main() 12 { 13 Student s; 14 ofstream outfile("E:\\stu.dat", ios::out | ios::binary); 15 16 while (cin >> s.name >> s.score) 17 { 18 if (strcmp(s.name, "exit") == 0) 19 { 20 break; 21 } 22 outfile.write((char*)&s, sizeof(s)); 23 } 24 outfile.close(); 25 26 ifstream infile("E:\\stu.dat", ios::in | ios::binary); 27 if (!infile) 28 { 29 cerr << "error" << endl; 30 } 31 32 //infile.get(c);读取一个字符 33 //outfile.put(c);写入一个字符 34 while (infile.read((char*)&s, sizeof(s))) 35 { 36 int ReadBytes = infile.gcount(); 37 cout << ReadBytes << " " << s.name << " " << s.score << endl; 38 } 39 infile.close(); 40 return 0; 41 }
五.若干特性
1 #include<iostream> 2 using namespace std; 3 4 int main() 5 { 6 bool flag = false; 7 cout << flag << endl; // 0 8 cout << boolalpha << flag << endl; // false,boolalpha强制让bool类型输出true和false 9 return 0; 10 }
1 #include<iostream> 2 #include<string> 3 using namespace std; 4 5 int main() 6 { 7 //枚举 8 enum Num{MinSize = 0, Mid, MaxSize = 1000, Last}; 9 Num x, y; 10 int i = MinSize, j = MaxSize; 11 cout << i << " " << j << endl; // 0 1000 12 cout << Mid << " " << Last << endl;//1 1001 13 14 //结构体默认public 15 struct Point1 16 { 17 }; 18 Point1 p1, p2; 19 20 typedef struct Point2 21 { 22 }*P; 23 P p3, p4; 24 25 //const 26 int b = 100, c = 1000; 27 28 const int *a = &b; 29 *a = 4;//error 30 a = &c; 31 b = 4; 32 33 int *const d = &b; 34 *d = 4; 35 d = &c;//error 36 37 const int *p1;int *p2; 38 p1 = new int(3); 39 p2 = new int(2); 40 p1 = p2;//ok 41 p2 = p1;//error 42 p2 = (int *)p1; 43 *p2 = 5; 44 cout << *p1 << endl;//5 45 46 return 0; 47 }
1 #include <iostream> 2 #include <string> 3 using namespace std; 4 5 int main(int argc, char *argv[]) 6 { 7 //<<和>> 比 关系,比较,逻辑,赋值,三目操作符等级高 8 int n = 1, m = 0; 9 cout << n < m << endl;//error 10 cout << (n < m) << endl; 11 return 0; 12 }
1 #include <iostream> 2 #include <string> 3 #include <fstream> 4 using namespace std; 5 6 int v = 10; 7 int main(int argc, char *argv[]) 8 { 9 int v = 5; 10 cout << v << endl; // 5 局部覆盖全局 11 cout << ::v << endl; // 10 全局 12 return 0; 13 }
六.输入输出
cerr:打印出错信息,不使用缓冲区,直接从屏幕输出
clog:打印出错信息,使用缓冲区,缓冲区满或者刷新时才输出到屏幕
1 ofstream out("text.txt", "w", stdout); 2 3 if (y == 0) 4 { 5 cerr << "error" << endl; 6 } 7 else 8 { 9 cout << x / y; 输出到text.txt文件,不是打印 10 }
七.typeid
1 #include <iostream> 2 #include <typeinfo> 3 using namespace std; 4 5 int main() 6 { 7 float x; 8 cout << (typeid(x) == typeid(float)) << endl; // true 9 cout << typeid(x).name() << endl; //float 10 return 0; 11 }