Write to file in thread, C++

Question

I wrote a program, which should write "1" in thread for three seconds. But when I try to debug or add controls outputs, I realize that the thread often isn't created (no outputs in the console or achievements of debug point). When I check the return value of CreateThread(), it's ok. I read about log in file for I/O, but I think I don't need it. I want a program with two threads; one writing "1" for three seconds, and the second writing "2" for three seconds. Then, compare the result. Doesn't matter if "1" and "2" are mixed in the input file.

#include <iostream>
#include <fstream>
#include <windows.h>
#include <stdio.h>
#include <WinBase.h>
#include <ctime>

#define NTHREAD 2

std::ofstream myfile;

DWORD WINAPI fce1 (LPVOID a){
    time_t timerStart, timerNow;
    time(&timerStart);
    timerNow = timerStart;
    while((timerNow - timerStart) < 3)
    {
        myfile << "1";
        myfile.flush();
        time(&timerNow);
    }
    return 0;
}


int main()
{
    HANDLE threads[NTHREAD];
    DWORD dwThreads[NTHREAD];

    myfile.open("file.txt");
    threads[0] = CreateThread(NULL, 0, fce1, NULL, 0, &dwThreads[0]);
    if (threads[0] == NULL){
        printf("Error\n");
    }

    myfile.close();
    return 0;
}

Answer 1

The problem is that your main program closes the file and exits before the thread has finished running, that means that the thread might attempt to write to a closed file and that it will be killed with the process.

You must wait for the thread to finish before exiting the process. You can do this by, for example, using GetExitCodeThread to poll for when the thread has exited.