c - 使用 readdir() 读取目录时删除文件

Question

我的代码是这样的:

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);

(此代码未经测试，纯属示例)

关键是:是否允许在使用 readdir() 遍历目录时删除目录中的文件？还是 readdir() 仍会找到已删除的 .log 文件？

Answer 1

引自 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.

所以，我的猜测是......这取决于。

这取决于操作系统、一天中的时间、添加/删除文件的相对顺序、...

此外，在 readdir() 函数返回和您尝试 unlink() 文件之间，某些其他进程可能已经删除了该文件文件和你的 unlink() 失败。

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编辑

我用这个程序测试过:

#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;
}

在我的计算机上，readdir() 找到已删除的文件，但找不到在 opendir() 和 readdir() 之间创建的文件。但是在另一台计算机上可能会有所不同；如果我用不同的选项编译，它在我的电脑上可能会有所不同；如果我升级内核可能会有所不同； ...