C Programming Question

Makaveli.2003 · 02-28-2003, 07:16 AM

Im new to C Programming and have been workin on afew examples off the internet, but I cant seem to work out what these 2 programs do, could some1 please tell me what these programs do, and help me understand what each line does? plz, thx in advance.

Code:

main()
{
 	 printf("My pid = %d.  My parent's pid = %d\n", getpid(), getppid());
}

Code:

fatal(s)
char *s;
{
	perror(s);
	exit(1);
}

main()
{
	int pid;

	pid = fork();
	printf("The PID is %d\n",pid);
	if(pid > 0)
	{
		wait((int *)0);
		printf("ls completed\n");
		exit(0);
	}

	if (pid == 0)
	{
		execl("/bin/ls", "ls", "-l", (char *)0);
		fatal("execl failed");
	}
	fatal("fork failed");
}

loke137 · 02-28-2003, 08:20 AM

did you include the libraries in the beginning of the proguram ?

Code:

#include <stdio.h>

Also good programming practice is

Code:

int main()
{
.
code
.
return 0;
}

Hope it helps

Makaveli.2003 · 02-28-2003, 08:41 AM

Yea, I did, sorry I didnt cut n paste it properly. Can ne1 help?

wapcaplet · 02-28-2003, 12:06 PM

Most of the standard functions will come with manual pages. Type:

man printf
man getpid
man getppid
man fork

In brief, though: printf is used for formatted output, usually directed to the screen. It's the most commonly-used method of printing out text in C.

getpid is used on *NIX systems to retrieve the process ID number (i.e., if you type 'ps -a' you get a listing of running processes, and their ID numbers - getpid retrieves that number).

Similarly, getppid retrieves the process parent's ID (the process that started that process running).

fork causes a running process to split off into two processes, both of which continue running at the fork point.

aditya · 03-03-2003, 06:34 AM

Hi,
the programs are pretty simple. Have you read process management.
read some material on process creation.
A parent process creates a child process by forking. So in the first program the main functionis giving it's identifier as well as the process identifier of the process that created it.

The 2nd program creates a new process. read the details of fork. It's easy.

hope that helps.

bye

aditya