如何将double值更改为四位小数值

#include<stdio.h>

int main() {
    double num = 3.1415926535;
    printf("%.4lf\n", num);
    return 0;
}

#include<iostream>
#include <iomanip>

int main() {
    double num = 3.1415926535;
    std::cout<< std::setprecision(4)<< num<< std::endl;
    return 0;
}

#include<stdio.h>

int main() {
    double num = 3.1415926535;
    char str[10];
    sprintf(str, "%.4lf", num);
    printf("%s\n", str);
    return 0;
}

#include<iostream>
#include <iomanip>

int main() {
    double num = 3.1415926535;
    std::cout<< std::fixed<< std::setprecision(4)<< num<< std::endl;
    return 0;
}