尝试计算两个时间之间的差，不会相减

我的程序所做的是，它首先打印当前时间，然后用户按 Enter 键。然后它再次打印出时间并计算用户等待按 Enter 键的时间。

我没时间做减法。我从 stackoverflow 中的另一个问题中得到了打印当地时间的代码。

#include <iostream>
#include <ctime>
using namespace std;

void main()
{
    time_t rawtime;
    struct tm * timeinfo;

    time ( &rawtime );
    timeinfo = localtime ( &rawtime );
    printf ( "Current local time and date: %s", asctime (timeinfo) );

    cout << "Press enter" << endl;
    cin.ignore();

    time_t rawtime2;
    struct tm * timeinfo2;

    time ( &rawtime2 );
    timeinfo2 = localtime ( &rawtime2 );
    printf ( "Later local time and date: %s", asctime (timeinfo2) );

    printf ( "You took %s", ( asctime (timeinfo2) - asctime (timeinfo) ) ); //math won't work here
    printf ( " seconds to press enter. ");
    cout << endl;
}

cout << "Elapsed time: " << rawtime2 - rawtime << " seconds" << endl;