Question about fork and exec

I'm a newbie to processes in general and i have this code:

Code:

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#include <sys/stat.h>
#include <fcntl.h>
#include <sys/types.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>


int main() {
        char buffer[100];
        int pid, status;
        while(1) {
                printf("> ");
                fgets(buffer, sizeof(buffer), stdin);
                printf("here\n");
                switch(pid = fork()) {
                        case 0 :
                                system(buffer);
                }
                waitpid(pid, &status, 0);
        }
}

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( there are too many includes, i know :) ).

I have to simulate a shell for a university homework and i have the following problem:
Wherever i run this, i read a command from the keyboard and the "here" print always comes AFTER the command's output. Why is this happening? It's very important for my homework.

Stelian

Try to flush the output buffer using fflush after printf("here")

Very likely the command's output is to stderr, and not stdout. Stderr is not buffered, and is a separate stream, so it is possible for stderr output to appear while stdout still has unflushed content.

Use fflush like Shaki says or:

Code:

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fprintf(stderr, "here\n");

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Thank you! fflush seems to be the solution

On a side note, system() returns normally, so you're leaving a lot of zombies behind. You need to terminate the child process after calling system(), or better yet, use some exec() variant instead.