[C++11] Mutual conversion between string and int

int to string

defined in the header file<string>

std::string to_string( int value );
std::string to_string( long value );
std::string to_string( long long value );
std::string to_string( unsigned value );
std::string to_string( unsigned long value );
std::string to_string( unsigned long long value ) ; 
std::string to_string( float value );
std::string to_string( double value );
std::string to_string( long double value );
1)把有符号十进制整数转换为字符串，与std::sprintf(buf，"%d" ,value)在有足够大的buf时产生的内容相同。
2)把有符号十进制整数转换为字符串，与std::sprintf(buf，"%ld",value)在有足够大的 buf时产生的内容相同。
3)把有符号十进制整数转换为字符串，与std::sprintf(buf，"%lld",value)在有足够大的buf时产生的内容相同.
4)把无符号十进制整数转换为字符串，与std::sprintf(buf，“%su"，value)在有足够大的 buf时产生的内容相同。
5)把无符号十进制整数转换为字符串，与std::sprintf(buf，"%lu"，value)在有足够大的 buf时产生的内容相同.
6)把无符号十进制整数转换为字符串，与std::sprintf(buf，"%llu"，value)在有足够大的 buf时产生的内容相同.
7,8)把浮点值转换为字符串，与std::sprintf(buf，"%f"，value)在有足够大的 buf时产生的内容相同。
9)把浮点值转换为字符串，与std::sprintf(buf，"%Lf",value)在有足够大的buf时产生的内容相同。

Specific use:

#include <iostream>
#include <string>
 
int main() 
{
    
    
    double f = 23.43;
    double f2 = 1e-9;
    double f3 = 1e40;
    double f4 = 1e-40;
    double f5 = 123456789;
    std::string f_str = std::to_string(f);
    std::string f_str2 = std::to_string(f2); // 注意：返回 "0.000000"
    std::string f_str3 = std::to_string(f3); // 注意：不返回 "1e+40".
    std::string f_str4 = std::to_string(f4); // 注意：返回 "0.000000"
    std::string f_str5 = std::to_string(f5);
    std::cout << "std::cout: " << f << '\n'
              << "to_string: " << f_str  << "\n\n"
              << "std::cout: " << f2 << '\n'
              << "to_string: " << f_str2 << "\n\n"
              << "std::cout: " << f3 << '\n'
              << "to_string: " << f_str3 << "\n\n"
              << "std::cout: " << f4 << '\n'
              << "to_string: " << f_str4 << "\n\n"
              << "std::cout: " << f5 << '\n'
              << "to_string: " << f_str5 << '\n';
}

You can also do this directly:

int x = 10;
string xx = to_string(x);   // 整数变字符串

string to int

std::stoi,std::stol,std::stolldefined in the header file<string>

#include <iostream>
#include <string>
 
int main()
{
    
    
    std::string str1 = "45";
    std::string str2 = "3.14159";
    std::string str3 = "31337 with words";
    std::string str4 = "words and 2";
 
    int myint1 = std::stoi(str1);
    int myint2 = std::stoi(str2);
    int myint3 = std::stoi(str3);
    // 错误： 'std::invalid_argument'
    // int myint4 = std::stoi(str4);
 
    std::cout << "std::stoi(\"" << str1 << "\") is " << myint1 << '\n';
    std::cout << "std::stoi(\"" << str2 << "\") is " << myint2 << '\n';
    std::cout << "std::stoi(\"" << str3 << "\") is " << myint3 << '\n';
    //std::cout << "std::stoi(\"" << str4 << "\") is " << myint4 << '\n';
 
}

You can also do this directly:

int y = stoi("11");  // 字符串变整型

Reference : Link

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