Page History

...

If the intent of the programmer is to remove the file referenced by new_file if it exists prior to calling rename(), this code example is non-compliant on Windows platforms because it rename() will fail, returns a nonzero value, and sets errno to EACCES.

char const *old_file = /* ... */;
char const *new_file = /* ... */;
if (rename(old_file, new_file) != 0) {
  /* Handle Error */
}

...

On Windows systems, it is necessary to explicitly remove the file referenced by new_file before calling rename(), if you want the file to be overwritten and the rename() operation to succeed.

char const *old_file = /* ... */;
char const *new_file = /* ... */;

if (_access_s(new_file,0) == 0) {
  if (remove(new_file) != 0) {
    /* Handle error condition */
  }
}

if (rename(old_file, new_file) != 0) {
  /* Handle error condition */
}

This code contains an unavoidable race condition conditions between the call to calls to _access_s(), remove() and the call to rename() and can consequently only be safely executed within a secure directory (see FIO17-A. Ensure that file operations are performed in a secure directory).

...

On POSIX systems, if the file referenced by new_file exists prior to calling rename(), the file is automatically removed.

char const *old_file = /* ... */;
char const *new_file = /* ... */;
if (rename(old_file, new_file) != 0) {
  /* Handle error condition */
}

...

If the desired behavior is to ensure that any file referenced by new_file is not removed, POSIX programmers must write implement additional codesafe guards.

Non-Compliant Code Example (POSIX)

If the intent of the programmer is to not remove the file referenced by new_file if it exists prior to calling rename(), this This code example is non-compliant because on POSIX systems the file is removedif new_file exists it will be removed by rename().

char const *old_file = /* ... */;
char const *new_file = /* ... */;
if (rename(old_file, new_file) != 0) {
  /* Handle Error */
}

...