Delete files while reading directory with readdir()

Question

My code is something like this:

DIR* pDir = opendir("/path/to/my/dir");
struct dirent pFile = NULL;
while ((pFile = readdir())) {
   // Check if it is a .zip file
   if (subrstr(pFile->d_name,".zip") {
      // It is a .zip file, delete it, and the matching log file
      char zipname[200];
      snprintf(zipname, sizeof(zipname), "/path/to/my/dir/%s", pFile->d_name);
      unlink(zipname);
      char* logname = subsstr(zipname, 0, strlen(pFile->d_name)-4); // Strip of .zip
      logname = appendstring(&logname, ".log"); // Append .log
      unlink(logname);
}
closedir(pDir);

(this code is untested and purely an example)

The point is: Is it allowed to delete a file in a directory while looping through the directory with readdir()? Or will readdir() still find the deleted .log file?

Answer 1

Quote from POSIX readdir:

If a file is removed from or added to the directory after the most recent call to opendir() or rewinddir(), whether a subsequent call to readdir() returns an entry for that file is unspecified.

So, my guess is ... it depends.

It depends on the OS, on the time of day, on the relative order of the files added/deleted, ...

And, as a further point, between the time the readdir() function returns and you try to unlink() the file, some other process could have deleted that file and your unlink() fails.

---

Edit

I tested with this program:

#include <dirent.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <unistd.h>

int main(void) {
  struct dirent *de;
  DIR *dd;

  /* create files `one.zip` and `one.log` before entering the readdir() loop */
  printf("creating `one.log` and `one.zip`\n");
  system("touch one.log"); /* assume it worked */
  system("touch one.zip"); /* assume it worked */

  dd = opendir("."); /* assume it worked */
  while ((de = readdir(dd)) != NULL) {
    printf("found %s\n", de->d_name);
    if (strstr(de->d_name, ".zip")) {
      char logname[1200];
      size_t i;
      if (*de->d_name == 'o') {
        /* create `two.zip` and `two.log` when the program finds `one.zip` */
        printf("creating `two.zip` and `two.log`\n");
        system("touch two.zip"); /* assume it worked */
        system("touch two.log"); /* assume it worked */
      }
      printf("unlinking %s\n", de->d_name);
      if (unlink(de->d_name)) perror("unlink");
      strcpy(logname, de->d_name);
      i = strlen(logname);
      logname[i-3] = 'l';
      logname[i-2] = 'o';
      logname[i-1] = 'g';
      printf("unlinking %s\n", logname);
      if (unlink(logname)) perror("unlink");
    }
  }
  closedir(dd); /* assume it worked */
  return 0;
}

On my computer, readdir() finds deleted files and does not find files created between opendir() and readdir(). But it may be different on another computer; it may be different on my computer if I compile with different options; it may be different if I upgrade the kernel; ...