C++中字符串与整型及浮点型转换全攻略

#include <string.h>
#include <iostream>
using namespace std;
int main() {
    string s = "123.123";
    char a[101];
    strcpy(a, s.c_str());
    // strcpy(a, s.data());  // 与上方语句等价，任选其一即可
    cout << a << endl;

    // 虽然传递的是地址，但是程序会将内容直接复制到 char [] 中，所以此处改变s不影响a
    s = "456.456";
    cout << a << endl;

    return 0;
}

#include <bits/stdc++.h>
using namespace std;
int main() {
    char a[100] = "123.123";
    string s = a;
    cout << s;
    return 0;
}

#include <stdlib.h>
#include <iostream>
using namespace std;
int main() {
    char a_chars[101] = "123.123";
    int a_int = atoi(a_chars);
    double a_double = atof(a_chars);
    cout << a_int << endl;
    cout << a_double << endl;

    return 0;
}

#include <stdlib.h>
#include <iostream>
using namespace std;
int main() {
    char a_chars[101] = "00123";
    int a_int = atoi(a_chars);
    cout << a_int << endl;

    char b_chars[101] = "-013.470";
    double b_double = atof(b_chars);
    cout << b_double << endl;

    return 0;
}

#include <stdlib.h>
#include <iostream>
using namespace std;
int main() {
    char a_chars[101] = "00123";
    long a_long = atol(a_chars);  // long
    cout << a_long << endl;
    long long a_long_long = atoll(a_chars);  // long long
    cout << a_long_long << endl;

    return 0;
}

#include <stdio.h>
using namespace std;
int main() {
    char a[1001];
    sprintf(a, "%.10lf", 3.1415926535);
    printf("%s", a);

    return 0;
}

#include <iostream>
using namespace std;
int main() {
    string s = to_string(123);
    cout << s << endl;
    return 0;
}

#include <stdlib.h>
#include <iostream>
using namespace std;
int main() {
    int INT = 123;
    long LONG = 123456;
    long long LONG_LONG = 123456789;
    char s[16] = {0};
    itoa(INT, s, 10);  // 要转换的数，存放结果的字符串，结果进制数（下同）
    cout << s << endl;
    ltoa(LONG, s, 10);
    cout << s << endl;
    lltoa(LONG_LONG, s, 10);  // 这里编译时有warning，原因不详
    cout << s << endl;

    return 0;
}

#include <stdlib.h>
#include <iostream>
using namespace std;
int main() {
    int INT = 12;
    char s[16] = {0};
    itoa(INT, s, 2);  // 12转二进制
    cout << s << endl;
    itoa(INT, s, 8);  // 转八进制
    cout << s << endl;
    itoa(INT, s, 16);  // 十六进制
    cout << s << endl;

    return 0;
}

#include <stdio.h>
#include <string.h>
using namespace std;
int main() {
    string str = "123";
    printf("str:%s", str.c_str());
    // printf("str:%s", str);  // 这样写真的不行
 
    return 0;
}