[SOLVED] How to use select with stdout?

How to use select with stdout?

I have the following code

    fd_set          set;
    struct          timeval timeout;
    printf("first printf\n"); // displayed
    FD_ZERO(&set);
    timeout.tv_sec = 1;

    FD_SET(fileno(stdout), &set);
    if (select(FD_SETSIZE, NULL, &set, NULL, &timeout)!=1)
    {
        stdout_closed = true;
        return;
    }
    printf("second printf\n"); // Not displayed

I m trying to check the ability to write to the stdout before printf("second printf\n");. but with this code, the select return a value != 1 and then the printf remain unreacheable. it looks like the select return "not possible" to write to the stdout.

Could you explain this behavior?

Solution

The call to select() is returning -1, and errno is 22 (invalid argument) because you've got junk values in the timeout. Try this:

FD_ZERO(&set);
timeout.tv_sec = 1;
timeout.tv_usec = 0; /* ADD THIS LINE to initialize tv_usec to 0 so it's valid */

and it should work.