Question

I have a simple example:

#include <stdio.h>
#include <errno.h>

int main() {
  int result = rename("filea", "doesntexist/fileb");
  if (result != 0) {
    printf("NOOOO %d\n", errno);
  }
  return 0;
}

and I want to distinguish between 2 of the possible failures:

1. filea doesn’t exist
2. directory for fileb doesn’t exist

but it always returns errno = 2 when either doesn’t exist… uhm
Any ideas how can I approach this?

Thanks

EDIT: If possible without manually checking if the files exist.

EDIT2: Not checking if the file exists is a stupid constraint 😉 so, I’ve accepted one of the answers already. Thanks!

Answer 1

I don’t know how you’re going to check if a file exists without checking if a file exists, but hopefully this function will help you out:

#include <sys/stat.h>

if (!fileExists("foo")) { /* foo does not exist */ }

int fileExists (const char *fn)
{
    struct stat buf;
    int i = stat(fn, &buf);
    if (i == 0)
        return 1; /* file found */
    return 0;
}

If your goal is to keep the code clean, then just use functions:

int main() 
{
    if (! renameFiles("fileA", "fileB")) { 
        fprintf(stderr, "rename failed...\n"); 
        exit EXIT_FAILURE; 
    }
    return EXIT_SUCCESS;
}

int renameFiles(const char *source, const char *destination)
{
    int result = -1;

    if ( (fileExists(source)) && (!fileExists(destination)) )
        result = rename(source, destination);

    if (result == 0)
        return 1; /* rename succeeded */

    /* 
        Either `source` does not exist, or `destination` 
        already exists, or there is some other error (take 
        a look at `errno` and handle appropriately)
    */

    return 0; 
}

You could return custom error codes from renameFiles() and conditionally handle errors based on which file does or does not exist, or if there is some other problem with the rename() call.