#include <stdio.h>
#include <signal.h>
#include <unistd.h>

void handler(int signum)
{
    FILE *fp;
    fp = fopen("test.txt", "w");
    fprintf(fp, "coucou, je suis bien en vie!\n");
    fclose(fp);
}

int main()
{
    signal(SIGUSR1, handler);
    for (size_t i = 0; i < 30; i++)
    {

        printf("i = %d, In main\n", i);
        sleep(1);
    }
    return 0;
}