execvp-ls：fts_open：没有这样的文件或目录

Question

I'm currently struggling with this error. I'm writing a shell emulator, using fork() for executing a command using execvp();. Almost every command I try to parse to my shell is working perfectly, except for ls without arguments. If I try to execute ls -lah, everything works, but a simple ls won't, receiving the following error:

ls: fts_open: No such file or directory

Here is a snippet of my code: (just the essential)

pid = fork();
      if (pid==0)
      {
        puts("CHILD");
        puts(args[0]);
        puts(args[1]);
        printf("%d\n", strlen(args[1]));
        args[2] = NULL;
        execvp(args[0], args);
      }
      else wait(NULL);
      puts("BACK TO PARENT");
    }

and here is the output for ls:

ls
CHILD
ls

0
ls: fts_open: No such file or directory
BACK TO PARENT

as you can see, args[0] contains ls, args[1] is empty, as there are no arguments, the length of args[1] is 0, but i keep getting the error.

Any idea on what it could be?

EDIT:

Kudos for Jonathan Leffler for finding it out: (also, it seems like it is just an issue on Mac)

The point is that args[1] is not really empty, so, the OS tries to open the '' file, which, obviously, does not exists, and, by what is looks, can't be created, since it is not really a name.

So, Here is what I did: check the len of args[1]. If it is 0, set it to NULL. (just freeing the memory did not really helped)

pid = fork();
      if (pid==0)
      {
        puts("CHILD");
        puts(args[0]);
        puts(args[1]);
        if (strlen(args[1]) == 0)
            args[1] = 0;
        args[2] = NULL;
        execvp(args[0], args);
      }
      else wait(NULL);
      puts("BACK TO PARENT");
    }

Answer 1

If there are no more arguments, the pointer should be null, not a non-null pointer to a zero length string.

pid = fork();
if (pid==0)
{
    puts("CHILD");
    puts(args[0]);
    fflush(stdout);
    args[1] = 0;
    execvp(args[0], args);
    fprintf(stderr, "Failed to exec %s\n", args[0]);
    exit(1);
}
else
    wait(NULL);
puts("BACK TO PARENT");

Just out of pure curiosity, I tried this at my command line:

$ ls ''
ls: fts_open: No such file or directory
$

Are you running on a Mac too? (To say I was surprised to see the same message doesn't begin to describe my reaction!) What's more intriguing is that creating a file fts_open doesn't seem to get rid of the error message. Weird behaviour by ls , but in response to an invalid request (there are no file names that are the empty string).