C – fork a child process using vfork()

/* creates a child process using vfork().
 * the child increments a global variable (glob)
 * and a local one (var) and returns
 * the corresponding process id of the 
 * respective process .
 * with vfork() the child uses the same
 * environment as the parent, so if
 * the child changes these values, the 
 * parent uses the changed ones too.*/
#include <sys/types.h> 
#include <stdlib.h>
#include <unistd.h>

int glob=66;
char buf[]="string to be outputed to stdout\n";

int main(void)
{
    int var=88;
    pid_t pid;
/* The `pid_t' data type is a signed integer type which is capable of
 * representing a process ID.  In the GNU library, this is an `int'.
 */
    if (write(STDOUT_FILENO, buf, sizeof(buf)-1)!=sizeof(buf)-1)
/* ssize_t write(int fd, const void *buf, size_t count);
 * writes up to count bytes to the file referenced by the file descriptor fd from the buffer starting at
 * buf
 * On  success, the number of bytes written are returned
 */
    /* if it didn't wrote the whole string to stdout */
    	{
	    printf("write to stdout failed\n");
	    exit(1);
	    /* normal exit */
	}
    printf("i'm gonna give birth to a child now\n");
    if ((pid=vfork())<0)
	/* vfork - create a child process and block the parent */
    	{
	    printf("damn. child died at birth.\n");
	    exit(2);
	}
    else
	if (pid==0)
	/* vfork() returns pid=0 to the child process and the pid of the child
	 * to the parrent. so, if pid=0, we are in the child process */
	    {
		printf("Lookie here, i am a kid and my pid is %d. My parent is %d.\n", getpid(),getppid());
		/* getpid  returns the process ID of the current process.
		 * getppid returns the process ID of the parent of the current process. */
		glob++;
		var++;
	    }
    printf("My pid is %d, glob=%d, var=%d\n", getpid(), glob, var);
    exit(0);
}