How to create a process on Mac OS using fork() and exec()

Question

I am working on a relatively simple, independent "process starter" that I would like to get to work on Windows (XP, Vista, 7), Linux (Ubuntu 10.10) and especially Mac OS X (10.6). Linux and Windows basically work, but I'm having some trouble with the Mac version. I was hoping fork() and exec() functions would work the same way under Mac OS as they work in Linux. So my first question is:

1. Should I use these to create a process on the Mac or are there any platform specific functions to be used?

My current code (which worked fine under Linux) to debug this looks something like this:

pid_t processId = 0;
if (processId = fork()) == 0)
{
    const char * tmpApplication = "/Path/to/TestApplication";

    int argc = 1;
    char * argv[argc + 1];

    argv[0] = tmpApplication;
    argv[1] = NULL;

    execv(tmpApplication, argv);
}else
{
    //[...]
}

Any idea if this could work under Mac OS X as well, because my child process is simply not being launched, while there are no errors that would come up.

Thank you!

Answer 1

The following program, adapted from your code, works just fine for me under OS X:

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

int main (void) {
    pid_t processId;
    if ((processId = fork()) == 0) {
        char app[] = "/bin/echo";
        char * const argv[] = { app, "success", NULL };
        if (execv(app, argv) < 0) {
            perror("execv error");
        }
    } else if (processId < 0) {
        perror("fork error");
    } else {
        return EXIT_SUCCESS;
    }
    return EXIT_FAILURE;
}

I suggest you start with this simple fragment, and if it works keep adding things until you find what makes it break.

Answer 2

Is TestApplication an actual executable, or an application bundle (.app)? You can only launch actual executables using functions like execv(). Usually the executable inside an application bundle can be found at ApplicationName.app/Contents/MacOS/ApplicationName.