C++标准库string学习笔记
string概述
作为c++语言用作字符串处理的标准库，和Python字符串类型有较多相似之处。可以使用‘=’进行赋值，“==”来比较，“+”进行拼接。
构造函数
- string s;直接声明变量
- string s(str);创建一个str的副本s
- string s(str,idx)；将str字符串索引值及其后面的部分当做s初值
- string s(str,idx,len);将str从idx开始，长度为len的内容赋值给s
- string s(c-str);将char*字符串作为字符串s初值
- string s(chars,len);以字符数组的前len个元素作为s初值
- string s(num,c);生成num个c字符的字符串。c为int类型
- string s(begin,end);将[begin， end]区间内的字符做为s初值,begin,end为可迭代对象
- string s(init-list);将init-list内字符做为s初值
示例代码
点击查看代码
#include <iostream>
#include <string>
#include <cstring>
using namespace std;
int main() {
/*构造字符串*/
string str1="hello world";
cout<<"str1:"<<str1<<endl;
string str2(str1);
cout<<"str2:"<<str2<<endl;
string str3(str1,2);
cout<<"str3:"<<str3<<endl;
string str4(str1,2,3);
cout<<"str4:"<<str4<<endl;
char word[20]="new string";
string str5(word,5);
cout<<"str5:"<<str5<<endl;
string str6(word);
cout<<"str6:"<<str6<<endl;
string str7(&str6[2],&str6[7]);
cout<<"str7:"<<str7<<endl;
char *a="c-----string";
string str8(a,5);
cout<<"str8:"<<str8<<endl;
string str9(a);
cout<<"str9:"<<str9<<endl;
string str10(10,121);
cout<<"str10:"<<str10<<endl;
return 0;
}
输出结果为：
----------------------------------------
str1:hello world
str2:hello world
str3:llo world
str4:llo
str5:new s
str6:new string
str7:w str
str8:c----
str9:c-----string
str10:yyyyyyyyyy
进程已结束，退出代码为 0
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string值操作
- =,assign(str);直接赋值，相互等价
- swap(str1,str2);将str1与str2值交换
- +，append(str)；字符串拼接
- push_back(c);c为int类型
- pop_back();移除末尾字符
- insert(pos,str);指定pos处添加str
- erase(i);保留前i位字符，i<=str.size()
- resize(len);保留前len位字符,长度不够则补位；
示例代码
点击查看代码
#include <iostream>
#include <string>
#include <cstring>
using namespace std;
int main() {
string str1="hello world";
cout<<"str1:"<<str1<<endl;
/*赋值操作*/
str1="你好";
cout<<"str1:"<<str1<<endl;
str1.assign("a new string!");
cout<<"str1:"<<str1<<endl;
string str2;
str2.assign("1234567");
cout<<"str2:"<<str2<<endl;
swap(str1,str2);
cout<<"str1:"<<str1<<endl;
cout<<"str2:"<<str2<<endl;
str2.append(",ok");
cout<<"str2:"<<str2<<endl;
str1+="10";
cout<<"str1:"<<str1<<endl;
str1.push_back('1');
cout<<"str1:"<<str1<<endl;
str1.pop_back();
cout<<"str1:"<<str1<<endl;
str2.insert(3,"insert data");
cout<<"str2:"<<str2<<endl;
str2.erase(22);
cout<<"str2:"<<str2<<endl;
cout<<"str2大小:"<<str2.size()<<endl;
str1.resize(16);
cout<<"str1:"<<str1<<endl;
}
输出结果为：
----------------------------------------
str1:hello world
str1:你好
str1:a new string!
str2:1234567
str1:1234567
str2:a new string!
str2:a new string!,ok
str1:123456710
str1:1234567101
str1:123456710
str2:a ninsert dataew string!,ok
str2:a ninsert dataew strin
str2大小:22
str1:123456710
进程已结束，退出代码为 0
--------------------------------------------------
替换字符str.replace()
- str.replace(pos,n,str2);将str 从[pos]开始的n个元素用str2替代；
- str.replace(pos1,n1,str2,pos2,n2);将str 从[pos1]开始的n1个元素用str2从[pos2]开始的n2个元素替代；
- str.replace(i1,i2,k1,k2);将i1-i2元素用k1-k2元素代替，i1,i2,k1,k2均为可迭代对象
点击查看代码
#include <iostream>
#include <string>
using namespace std;
int main() {
string str3 = "0123456780000";
string str4 = "asdfghjkl@#$";
cout << "str3:" << str3 << endl;
cout << "str4:" << str4 << endl;
str4.replace(5, 5, str3);
cout << "str4:" << str4 << endl;
str4.replace(0, 7, str3, str3.find("2"), 4);
cout << "str4:" << str4 << endl;
str4.replace(str4.begin() + 3, str4.begin() + 5, str3.begin(), str3.end() - 3);
cout << "str4:" << str4 << endl;
}
输出结果：
--------------------------------------
str3:0123456780000
str4:asdfghjkl@#$
str4:asdfg0123456780000#$
str4:234523456780000#$
str4:23401234567803456780000#$
进程已结束，退出代码为 0
---------------------------------------
字符串与数字相互转换
字符串转数字
- stoi();转换为int型
- stol();转换为long int型
- stoll();转换为long long 型
- stoul();转换为 unsigned long型
- stoull();转换为unsigned long long 型
- stof();转换为float型
- stod();转换为double型
- stold();转换为long double型
- to_string();将数字转换为string；
点击查看代码
#include <iostream>
#include <string>
using namespace std;
int main() {
string str1 = "-12345";
string str2 = "-345.78888";
auto num1 = stoi(str1);
auto num2 = stol(str1);
auto num3 = stold(str1);
cout << "num1=" << num1 << endl;
cout << "num2=" << num2 << endl;
cout << "num3=" << num3 << endl;
string str3 = "12345";
auto num4 = stoul(str3);
auto num5 = stoull(str3);
cout << "num4=" << num4 << endl;
cout << "num5=" << num5 << endl;
auto num6 = stof(str2);
auto num7 = stod(str2);
auto num8 = stold(str2);
cout << "num6=" << num6 << endl;
cout << "num7=" << num7 << endl;
cout << "num8=" << num8 << endl;
auto num10=-12.3456;
auto str4= to_string(num10);
cout << "num10->str:" << str4 << endl;
}
输出结果
----------------------------------
num1=-12345
num2=-12345
num3=-12345
num4=12345
num5=12345
num6=-345.789
num7=-345.789
num8=-345.789
num10->str:-12.345600
进程已结束，退出代码为 0
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***不可将“-123"转换为unsigned 型，不可将“123.12”转换为int型,可以将“-1234”转换为浮点类型***
字符搜索和查找
- find()
- rfind()
- find_first_of()
- find_last_of()
- find_first_not_of()
- find_last_not_of()
实参(value,pos,n):
value:要查找的字符值
pos,开始查找的位置
n，查找范围
返回值，索引
示例代码
点击查看代码
#include <iostream>
#include <string>
using namespace std;
int main() {
string str1 = "In addition, some swarm intelligence methods that mimic\n "
"biological behaviors are also gradually applied to regional\n"
"coverage planning tasks. Reference proposed a rule-\n"
"based collaborative search algorithm based on the kinetic\n"
"model-Boids.";
cout<<str1.size()<<endl;
string str2(str1,100,10);
cout<<str2<<endl;
cout<<str1.find_first_of("t",100,100);
}
输出结果：
-------------------------------------
244
lied to re
104
进程已结束，退出代码为 0
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