CODEWITHSUNDEEP
clinux
Ivan Prodanov
Ivan Prodanov

Reputation: 35522

Why it does not return after execlp? Is it normal?

So I'm new to C and this is one problem I have and cannot understand. First, execlp() executes a program just by name(by searching for it) with parameters. Here I want to execute "who" with "-u" as parameter, but it does not return anything from execlp. Why? Is this normal?

    #include <stdio.h>
    #include <fcntl.h>
    #include <unistd.h>

    main()
    {
        int j = 0;
        if(fork() == 0)
        {
            j++;
            if(execlp("who", "who", "-u", (char*)0) == -1)
            {
                j++;
            }
            else
            {
                printf("\nStoinostta na j = %d", j);
                return;
            }
        }   
        else
        {
            --j;
            printf("\nStoinostta na j=%d", j);
        }
        printf("\nStoinostta na j ravno na %d", ++j);
    }

Upvotes: 1

Views: 677

Answers (3)

steveha
steveha

Reputation: 76715

As noted by @Charles Bailey, execlp() replaces the current process. So it never returns after running a program.

If you want to just run something, a simple way is with system(): http://linux.die.net/man/3/system

If you want to run something and control input and output, possibly collecting the output from the command, a good way is popen(): http://linux.die.net/man/3/popen

Upvotes: 3

luser droog
luser droog

Reputation: 19504

Perhaps you want the system function. It will run another program and then return.

Another option would be to exec after calling fork.

fork() || execlp(...);

Upvotes: 2

CB Bailey
CB Bailey

Reputation: 791929

On success, execlp replaces the current process with the command that you specify. It will only return if it fails. The manpage should make this clear.

Upvotes: 7

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