how to wait an exec finishes to write in pipe in C - c

Question

I'd like to know how to wait for my exec finish to write in an fd before use it?
The problem is the fact that not all of my exec is wrote in the pipe.
So when I get the answer, not all of the exec is wrote.
here is the part of the code concerned :
switch(fork()){
case -1:
perror("fork");
case 0:
// redirection de l'entré standard
close(fd[0]);
dup2(fd[1], 1);
dup2(fd[1], 2);
close(fd[1]);
// éxécution de la commande courrante.
execvp(d->command[0], d->command);
perror("execvp");
default:
// gère les processus zombies.
if(wait(NULL) == -1){
perror("wait");
}
char buffer[550000] = {0};
unlink(d->pipe1);
unlink(d->tube2);
unlink(tube2);
//création du tube nommé pour le client.
if(mkfifo(tube2, 0644) != 0)
{
perror("mkfifo");
fprintf(stderr, "Impossible de créer le tube nommé.\n");
exit(EXIT_FAILURE);
}
// ouverture de ce même tube
if((d->entree_tube = open(tube2, O_WRONLY)) == -1)
{
perror("open");
fprintf(stderr, "Impossible d'ouvrir l'entrée du tube nommé.\n");
exit(EXIT_FAILURE);
}
close(fd[1]);
// lecture du résultat de la commande stocké dans fd[0]
while (read(fd[0], buffer, sizeof(buffer)) != 0)
{
//écriture du résultat dans l'entré du tube.
if(write(d->entree_tube, buffer, strlen(buffer)) == -1){
perror("write");
}
//réinitialisation du buffer stockant une partie du résultat de la commande.
memset (buffer, 0, sizeof(buffer));
}
// on regarde si il y a eu le mot clé "fin" pour alerter la client que la commande est terminé
// et on redonne la main à un autre client tentant de se connecter au démon.
}
Thanks for helping.

Answer 1

I tried not to wait as you asked, but it doesn't resolve anything, and I don't see how can I read again datas by an other loop of read.
You don't need an other loop of read - the read loop you already have is just fine. You only have to move the wait() call behind that read loop. That's what John Bollinger meant when he wrote: You do want to wait eventually, but not while you have any other responsibilities to the child.