Linux Opendir and readdir will not update along with directory changing

Table of Contents

• 1. Result
• 2. temporary fix method
• 3. Test

1 Result

According to my experiment, opendir() will just record a static state of opened directory. During the readdir() operation, if you add/remove a file to the directory opened by opendir(), readdir() knows nothing about it.

2 temporary fix method

use access() to judge if some file existed.

3 Test

• touch files

~ddd$ touch a.tmp b.tmp c.tmp a.aa b.aa

• test

./readdir-test ddd

*******************************
a.aa  a.tmp  b.aa  b.tmp  c.tmp
*******************************
[0], full name is ddd/a.aa
[1], full name is ddd/..
[2], full name is ddd/c.tmp
=====================================
all .aa deleted.
a.tmp  b.tmp  c.tmp
=====================================
[3], full name is ddd/b.aa // shouldn‘t show b.aa now
ddd/b.aa not exist.
[4], full name is ddd/b.tmp
rm: cannot remove `ddd/*.aa‘: No such file or directory
=====================================
all .aa deleted.
a.tmp  b.tmp  c.tmp
=====================================
[5], full name is ddd/.
[6], full name is ddd/a.tmp
rm: cannot remove `ddd/*.aa‘: No such file or directory
=====================================
all .aa deleted.
a.tmp  b.tmp  c.tmp
=====================================

• code as below

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

int main(int argc, char *argv[])
{
    DIR *pdir = NULL;
    struct dirent *pdirent = NULL;
    char fname[256];
    char cmd[256];
    static int i = 0;

    if (argc != 2) {
        printf("Usage: %s dir\n", argv[0]);
        return -1;
    }

    pdir = opendir(argv[1]);
    if (pdir == NULL)
        return -1;

    printf("*******************************\n");
    sprintf(cmd, "ls %s", argv[1]);
    system(cmd);
    printf("*******************************\n");

    while ((pdirent = readdir(pdir)) != NULL) {

        sprintf(fname, "%s/%s", argv[1], pdirent->d_name);
        printf("[%d], full name is %s\n", i++, fname);

        if (access(fname, F_OK) != 0) {
            printf("%s not exist.\n", fname);
            continue;
        }

        if (strncmp(fname+strlen(fname)-4, ".tmp", 4) == 0) {

            sprintf(cmd, "rm %s/*.aa", argv[1]);
            system(cmd);

            printf("=====================================\n");
            printf("all .aa deleted.\n");
            sprintf(cmd, "ls %s", argv[1]);
            system(cmd);
            printf("=====================================\n");
        }
    }
    closedir(pdir);

    return 0;
}

Output result is