CS456 - Systems Programming Spring 2025

Displaying ./code/forkExec/forkExec.c

/*
 *  This is a sample program that uses fork and exec to execute a file
 *
 *
 *  This program will run the nextPowerof2 program in this directory
 *
 *	to compile
 *	> gcc -o forkExec forkExec.c
 *
 *	to run
 *	> ./forkexec
 *
 */


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

int main(int argc, char **argv){

	//no need for a usage statement, no command line args used here

	//setting up our arguments	
	char *args[] = {"nextPowerof2", "54"};
	/*
	 * args[0] = "nextPowerof2"
	 * args[1] = "54"
	 * this arg menu is silliar to the argv[] meny
	 */

	//printing out what we're running
	printf("> %s %s\n", args[0], args[1]);

	pid_t pid = fork(); // calling fork, store in pid

	//check if fork failed, if so: exit the program
	if(pid ==-1){
		perror("fork failed");
		exit(-1);
	}

		
	if(pid){
		//we are in the parent process	
		int status;
		waitpid(pid, &status, 0); //waiting for process to change state
		return 0;
	} else {
		//we're in the child process
		
		// we need to use a variant of exec to execute our  program
		// since we basically have command line arguments, we will use the "execv" argument
		// execv takes two arguments, 
		// 	- string containing the pathname to the program,
		// 	- array of strings containing all the args associated with the program
		//
		// so for our first argument, we pass in the name of the program which is in args[0]
		// and the second argument, we pass in a pointer to the array of arguments
		// 	// i could have just written "args" instead of &args[0] in this case,
		// 	// but suppose i was passing in argv[1] for the pathname, if i had args after that
		// 	// i'd need to pass in &argv[1] for the second argument to execv as that is the address
		// 	// of the pointer to argv[1]	
		//
		execv(args[0], &args[0]);
	}

	//then we're done!
	return 0;
}