如何调整std::cout输出数据的精度

 用std::cout.precision() 和 std::cout.setf() 函数

    double num = 1234567.1234567;

    std::cout <<  num << "\n";

    std::cout.setf(std::ios::fixed, std::ios::floatfield);
    std::cout << num << "\n";

    std::cout.precision(4);
    std::cout << num << "\n";

结果：

1.23457e+06
1234567.123457
1234567.1235