why this is not working? execl()

[nacho4d]

I know that exec() functions dont come back unless they fail.
that is why i created a child process so to parent process waits for the child.
But in my case the program does not come back. what am I missing?

/*
 *  main.c
 */

#include "execute.h"

main(){
	char *argument = "barbara.pgm";
	printf("executing invert:...\n");
	
	execute(2,argument);
	printf("ended.\n");
}

and the execute.h

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

static char *program[8] = {
			"./avgFilter", 
			"./binarize", 
			"./invert", 
			"", "", "", ""};

void execute(short progNumber, char * fileName){
	int pid;
	int status;
	
	/*
	 *	Get a child process
	 */
	if((pid = fork()) < 0){
		perror("fork: ");
		exit(EXIT_FAILURE);
	}
	
	/*
	 *	The child executes the program
	 */
	if(pid == 0){
		execl(program[progNumber],program[progNumber], fileName, (char *)0);
		perror("execl");
		exit(EXIT_FAILURE);
	}
	
	/*
	 *	The parent process just waits
	 */
	if (pid >= 1) {
		wait(&status);
	}
	
	exit(EXIT_SUCCESS);
}

[matsp]

What do you mean "program doesn't come back"? Does "ps" show the applciation running (invert in this case)?

Also, you should not implement functions in header files unless they are really short (inline functions).

--
Mats

[Elysia]

There are two other flaws in the program:
main should return int explicitly.
A function other than main should never call exit unless in very special cases! It's better to return an error and let main display an error and quit.

[nacho4d]

[QUOTE=matsp;711036]What do you mean "program doesn't come back"? Does "ps" show the applciation running (invert in this case)?

I mean the reason I created the function is because after doing "./invert barbara.pgm" i have to do something else , in this piece of code is just

printf("ended");

but this part is not been executing (as it seems)

the output is :

2:~nacho4d$
./main
executing invert:...
2:~nacho4d$

why?

[Salem]

Well you called exit(), even in the parent.
So yes, it never makes it to the printf() in main().

[matsp]

But, as Elysia pointed out, you are calling "exit()" from execute(), so it won't get back to main ever...

	exit(EXIT_SUCCESS);

will always be executed in your execute() function.

--
Mats

[nacho4d]

Now I see...
Thanks Salem and Matsp.
So, what is the difference between exit and return? can you explain my kindly?

I changed my program as you suggested and it works ok

[Elysia]

Exit terminates your program. Killing it. It won't execute further.
Return simply ends the function and returns to the previous function.

[nacho4d]

I C.
That is why calling exit from functions is dangerous right? in Others words it should only be called from main() right?

[Elysia]

Yes, except in very special situation which you don't really have to worry about very much.

[nacho4d]

thank you very much.