Waiting for execvp in main

int main()
{
    ...
    if(!fork())
        {
            execvp(cmdName,cmdParam);
        }
    printf("In 开发者_开发知识库main()...");
return(0);
}

1. Assuming I have correctly passed the cmdName & cmdParam arguments, how do I wait for the process created by execvp to finish, before resuming the execution of main()?
2. Does the execvp() create a process which is a child of the newly fork()ed process?

1. In the parent process, fork returns the PID of the child process, so you can store that in a variable, and then use waitpid to wait for the child process to terminate.

2. Not really - the new child process created by fork is a duplicate of the parent, and execvp then replaces its process image with a new image. Effectively you initially have two 'copies' of the parent, one of which then 'becomes' the new program.

As noted you need to save the value of the fork call. You should really use more than an if on the fork. There are three cases:

1. 0: you're the child process

2. 0: you're the parent and got a child PID back

3. -1: something horrible happened and fork failed

You really want to know about case 3, it'll ruin your whole day. (also the exec call)

int main() {
  int pid = fork();
  if(-1 == pid) {
     fprintf(stderr, "Big problems forking %s\n", strerror(errno);
     exit(-1);//or whatever
  }
  else if (0 == pid) {
    if (-1 == execvp(cmdName,cmdParam)) {
      //like above, get some output about what happened
    }
  }
  //no need to else here, execvp  shouldn't return 
  // if it does you've taken care of it above
  waitpid(pid, NULL, 0);
  printf("Resuming main()...");
}

return(0); }

For your first question:

Use waitpid(2) like this:

int pid = fork();
if (!pid)
  {
    execvp(cmdName, cmdParam);
  }
waitpid(pid, NULL, 0);
printf("Resuming main()...\n");

For the second part: all exec function calls take the process over (none of them return)

You need to store the return value of fork(), which returns a different value to each executable (0 if you are the child PID if you are the parent), and then you need to do a waitpid