Duplicate stdout and stderr from fork process to files

Question

I need to duplicate stdout and stderr of a child proccess to multiple files.
I understand that i can use tee(), but I haven\'t found e

Answer 1

Using tee and splice to write data from a handle to multiple other handles:

// Needs at least two targets, sentinel is INVALID_HANDLE_VALUE
int push_to_all(int source, ssize_t count, ...) {
    va_list vl;
    va_start(vl, count);
    int target = va_arg(vl, int), next = va_arg(vl, int);
    count = tee(source, target, count, SPLICE_F_NONBLOCK);
    if(count <= 0) { va_end(vl); return count; }
    while((target = next, next = va_arg(vl, int)) > 0) {
        tee(source, target, count, 0);
    va_end(vl);
    return splice(source, 0, target, 0, count, 0);
}