CODEWITHSUNDEEP
c
Rubiks
Rubiks

Reputation: 481

Can't get execvp to execute file

I am trying to write a program that will fork, then open a file and execute it. The file it should execute is called child and it has been compiled. When I type ./child, it runs. However, when I run this program it does not execute the child program and I am prompted with the error message I put in "Execution failed". What I am doing wrong?

This is my parent class

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



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

pid_t parent = getpid();
pid_t pid = fork();


if (pid == -1)
{
// error, failed to fork()
} 
else if (pid > 0)
{
int status;
 waitpid(pid, &status, 0);
}
else 
{

int var = execvp("./child", NULL);

if(var < 0)
{
    printf("Execution failed");
}

}
exit(0);   // exec never returns
}

This is the child

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


int main (int argc, char **argv)
{   
printf ("Im the child");
exit (0);
}

Upvotes: 0

Views: 989

Answers (1)

Matteo Ragni
Matteo Ragni

Reputation: 2956

I actually don't know what you are doing wrong. After a copy and a compilation (and several warning complains) your code runs fine (GCC 7.2).

Obviously, child must be in the same working directory in which you run your main executable (the one that forks).

But probably I would write that code in this way, but I'm not an expert in forking:

#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <sys/wait.h>
#include <errno.h>

extern int errno;

int main () {
  pid_t pid = fork();

  if (pid < 0) {
    fprintf(stderr, "%s\n", strerror(errno));
    return 1;
  }

  if (pid == 0) {
   int ret = execl("./child", "", (char *)NULL);
   if(ret < 0) {
     fprintf(stderr, "%s\n", strerror(errno));
     return 1;
   }
  } else {
    wait(NULL);
  }
  return 0;
}

At least it tells you which error execl has encountered.

Upvotes: 1

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