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详解C++中stoi/stol/stoll函数的用法

2023-03-23 11:09

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stoi()函数

#include <string>
int stoi(const std::string& str, std::size_t* pos = 0, int base = 10);
int stoi(const std::wstring& str, std::size_t* pos = 0, int base = 10);

功能：将字符串str转成 有符号 int 整数

参数：

stoi()函数指定转换字符串为十进制用法

#include <iostream>
#include <string>
using namespace std;
 
int main(int argc, char *argv[])
{
    int a;
    size_t pos = 0;
    string str;
 
    str = "-1235";
    a = stoi(str);
    cout << "a = " << a << endl; //a = -1235
 
    str = "1235";
    a = stoi(str);
    cout << "a = " << a << endl; //a = 1235
 
    str = "  -12  35"; 
    a = stoi(str, &pos); //会舍弃空白符
    cout << "a = " << a << endl; //a = -12
    cout << "pos = " << pos << endl; //pos = 5
 
    str = "  -12ab35";
    a = stoi(str, &pos);
    cout << "a = " << a << endl; //a = -12
    cout << "pos = " << pos << endl; //pos = 5
 
    str = "0123";
    a = stoi(str);
    cout << "a = " << a << endl; //a = 123
 
    str = "0x123";
    a = stoi(str);
    cout << "a = " << a << endl; //a = 0
 
    return 0;
}

stoi()函数指定转换字符串为十六进制用法

#include <iostream>
#include <string>
using namespace std;
 
int main(int argc, char *argv[])
{
    int a;
    size_t pos = 0;
    string str;
 
    str = "0x123";
    a = stoi(str, NULL, 16); //base = 16，指定十六进制
    cout << "a = " << a << endl; //a = 291
 
   str = "0x123";
    a = stoi(str, NULL, 0); //base = 0，自动检测数值进制
    cout << "a = " << a << endl; //a = 291
 
    str = "-12";
    a = stoi(str, &pos, 16); //-(2 + 1*16)
    cout << "a = " << a << endl; //a = -18
    cout << "pos = " << pos << endl; //pos = 3
 
    str = "12";
    a = stoi(str, &pos, 16); //2 + 1*16
    cout << "a = " << a << endl; //a = 18
    cout << "pos = " << pos << endl; //pos = 2
 
    str = "  -12  35"; 
    a = stoi(str, &pos, 16); //会舍弃空白符
    cout << "a = " << a << endl; //a = -18
    cout << "pos = " << pos << endl; //pos = 5
 
    str = "  -ab";
    a = stoi(str, &pos, 16); //-(11 + 10*16)
    cout << "a = " << a << endl; //a = -171
    cout << "pos = " << pos << endl; //pos = 5
 
    str = "0123";
    a = stoi(str, NULL, 16); //(3 + 2*16 + 1*16*16)
    cout << "a = " << a << endl; //a = 291
 
    return 0;
}

stoi()函数指定转换字符串为八进制用法

#include <iostream>
#include <string>
using namespace std;
 
int main(int argc, char *argv[])
{
    int a;
    size_t pos = 0;
    string str;
 
    str = "0x123";
    a = stoi(str, NULL, 8); //base = 8，指定八进制
    cout << "a = " << a << endl; //a = 0
 
   str = "0123"; //(3 + 2*8 + 1*8*8)
    a = stoi(str, NULL, 0); //base = 0，自动检测数值进制
    cout << "a = " << a << endl; //a = 83
 
    str = "-12";
    a = stoi(str, &pos, 8); //-(2 + 1*8)
    cout << "a = " << a << endl; //a = -10
    cout << "pos = " << pos << endl; //pos = 3
 
    str = "12";
    a = stoi(str, &pos, 8); //2 + 1*8
    cout << "a = " << a << endl; //a = 10
    cout << "pos = " << pos << endl; //pos = 2
 
    str = "  -12  35"; 
    a = stoi(str, &pos, 8); //会舍弃空白符
    cout << "a = " << a << endl; //a = -10
    cout << "pos = " << pos << endl; //pos = 5
 
    // str = "  -a78"; 
    // a = stoi(str, &pos, 8); //数字前有字母，调用会崩掉
    // cout << "a = " << a << endl; 
    // cout << "pos = " << pos << endl; 
 
    return 0;
}

stol()函数

#include <string>
long stol(const std::string& str, std::size_t* pos = 0, int base = 10);
long stol(const std::wstring& str, std::size_t* pos = 0, int base = 10);

功能：将字符串str转成 有符号 long 整数

参数：

stol()函数指定转换字符串为十进制用法

#include <iostream>
#include <string>
using namespace std;
 
int main(int argc, char *argv[])
{
    long a;
    size_t pos = 0;
    string str;
 
    str = "-1235";
    a = stol(str);
    cout << "a = " << a << endl; //a = -1235
 
    str = "1235";
    a = stol(str);
    cout << "a = " << a << endl; //a = 1235
 
    str = "  -12  35"; 
    a = stol(str, &pos); //会舍弃空白符
    cout << "a = " << a << endl; //a = -12
    cout << "pos = " << pos << endl; //pos = 5
 
    str = "  -12ab35";
    a = stol(str, &pos);
    cout << "a = " << a << endl; //a = -12
    cout << "pos = " << pos << endl; //pos = 5
 
    str = "0123";
    a = stol(str);
    cout << "a = " << a << endl; //a = 123
 
    str = "0x123";
    a = stol(str);
    cout << "a = " << a << endl; //a = 0
 
    return 0;
}

stol()函数指定转换字符串为十六进制用法

#include <iostream>
#include <string>
using namespace std;
 
int main(int argc, char *argv[])
{
    long a;
    size_t pos = 0;
    string str;
 
    str = "0x123";
    a = stol(str, NULL, 16); //base = 16，指定十六进制
    cout << "a = " << a << endl; //a = 291
 
   str = "0x123";
    a = stol(str, NULL, 0); //base = 0，自动检测数值进制
    cout << "a = " << a << endl; //a = 291
 
    str = "-12";
    a = stol(str, &pos, 16); //-(2 + 1*16)
    cout << "a = " << a << endl; //a = -18
    cout << "pos = " << pos << endl; //pos = 3
 
    str = "12";
    a = stol(str, &pos, 16); //2 + 1*16
    cout << "a = " << a << endl; //a = 18
    cout << "pos = " << pos << endl; //pos = 2
 
    str = "  -12  35"; 
    a = stol(str, &pos, 16); //会舍弃空白符
    cout << "a = " << a << endl; //a = -18
    cout << "pos = " << pos << endl; //pos = 5
 
    str = "  -ab";
    a = stol(str, &pos, 16); //-(11 + 10*16)
    cout << "a = " << a << endl; //a = -171
    cout << "pos = " << pos << endl; //pos = 5
 
    str = "0123";
    a = stol(str, NULL, 16); //(3 + 2*16 + 1*16*16)
    cout << "a = " << a << endl; //a = 291
 
    return 0;
}

stol()函数指定转换字符串为八进制用法

#include <iostream>
#include <string>
using namespace std;
 
int main(int argc, char *argv[])
{
    long a;
    size_t pos = 0;
    string str;
 
    str = "0x123";
    a = stol(str, NULL, 8); //base = 8，指定八进制
    cout << "a = " << a << endl; //a = 0
 
   str = "0123"; //(3 + 2*8 + 1*8*8)
    a = stol(str, NULL, 0); //base = 0，自动检测数值进制
    cout << "a = " << a << endl; //a = 83
 
    str = "-12";
    a = stol(str, &pos, 8); //-(2 + 1*8)
    cout << "a = " << a << endl; //a = -10
    cout << "pos = " << pos << endl; //pos = 3
 
    str = "12";
    a = stol(str, &pos, 8); //2 + 1*8
    cout << "a = " << a << endl; //a = 10
    cout << "pos = " << pos << endl; //pos = 2
 
    str = "  -12  35"; 
    a = stol(str, &pos, 8); //会舍弃空白符
    cout << "a = " << a << endl; //a = -10
    cout << "pos = " << pos << endl; //pos = 5
 
    // str = "  -a78"; 
    // a = stol(str, &pos, 8); //数字前有字母，调用会崩掉
    // cout << "a = " << a << endl; 
    // cout << "pos = " << pos << endl; 
 
    return 0;
}

stoll()函数

#include <string>
long long stoll(const std::string& str, std::size_t* pos = 0, int base = 10);
long long stoll(const std::wstring& str, std::size_t* pos = 0, int base = 10);

功能：将字符串str转成 有符号 long long 整数

参数：

stoll()函数指定转换字符串为十进制用法

#include <iostream>
#include <string>
using namespace std;
 
int main(int argc, char *argv[])
{
    long long a;
    size_t pos = 0;
    string str;
 
    str = "-1235";
    a = stoll(str);
    cout << "a = " << a << endl; //a = -1235
 
    str = "1235";
    a = stoll(str);
    cout << "a = " << a << endl; //a = 1235
 
    str = "  -12  35"; 
    a = stoll(str, &pos); //会舍弃空白符
    cout << "a = " << a << endl; //a = -12
    cout << "pos = " << pos << endl; //pos = 5
 
    str = "  -12ab35";
    a = stoll(str, &pos);
    cout << "a = " << a << endl; //a = -12
    cout << "pos = " << pos << endl; //pos = 5
 
    str = "0123";
    a = stoll(str);
    cout << "a = " << a << endl; //a = 123
 
    str = "0x123";
    a = stoll(str);
    cout << "a = " << a << endl; //a = 0
 
    return 0;
}

stoll()函数指定转换字符串为十六进制用法

#include <iostream>
#include <string>
using namespace std;
 
int main(int argc, char *argv[])
{
    long long a;
    size_t pos = 0;
    string str;
 
    str = "0x123";
    a = stoll(str, NULL, 16); //base = 16，指定十六进制
    cout << "a = " << a << endl; //a = 291
 
   str = "0x123";
    a = stoll(str, NULL, 0); //base = 0，自动检测数值进制
    cout << "a = " << a << endl; //a = 291
 
    str = "-12";
    a = stoll(str, &pos, 16); //-(2 + 1*16)
    cout << "a = " << a << endl; //a = -18
    cout << "pos = " << pos << endl; //pos = 3
 
    str = "12";
    a = stoll(str, &pos, 16); //2 + 1*16
    cout << "a = " << a << endl; //a = 18
    cout << "pos = " << pos << endl; //pos = 2
 
    str = "  -12  35"; 
    a = stoll(str, &pos, 16); //会舍弃空白符
    cout << "a = " << a << endl; //a = -18
    cout << "pos = " << pos << endl; //pos = 5
 
    str = "  -ab";
    a = stoll(str, &pos, 16); //-(11 + 10*16)
    cout << "a = " << a << endl; //a = -171
    cout << "pos = " << pos << endl; //pos = 5
 
    str = "0123";
    a = stoll(str, NULL, 16); //(3 + 2*16 + 1*16*16)
    cout << "a = " << a << endl; //a = 291
 
    return 0;
}

stoll()函数指定转换字符串为八进制用法

#include <iostream>
#include <string>
using namespace std;
 
int main(int argc, char *argv[])
{
    long long a;
    size_t pos = 0;
    string str;
 
    str = "0x123";
    a = stoll(str, NULL, 8); //base = 8，指定八进制
    cout << "a = " << a << endl; //a = 0
 
   str = "0123"; //(3 + 2*8 + 1*8*8)
    a = stoll(str, NULL, 0); //base = 0，自动检测数值进制
    cout << "a = " << a << endl; //a = 83
 
    str = "-12";
    a = stoll(str, &pos, 8); //-(2 + 1*8)
    cout << "a = " << a << endl; //a = -10
    cout << "pos = " << pos << endl; //pos = 3
 
    str = "12";
    a = stoll(str, &pos, 8); //2 + 1*8
    cout << "a = " << a << endl; //a = 10
    cout << "pos = " << pos << endl; //pos = 2
 
    str = "  -12  35"; 
    a = stoll(str, &pos, 8); //会舍弃空白符
    cout << "a = " << a << endl; //a = -10
    cout << "pos = " << pos << endl; //pos = 5
 
    // str = "  -a78"; 
    // a = stoll(str, &pos, 8); //数字前有字母，调用会崩掉
    // cout << "a = " << a << endl; 
    // cout << "pos = " << pos << endl; 
 
    return 0;
}

注意：stoi、stol、stoll 函数是C++11标准加入的，用g++编译器编译需要加参数：-std=c++11

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