How to implement file sorting by debian readdir

In Debian systems, the readdir function is used to read directory contents, but the order in which it returns is not predefined. To sort files in a directory, you need to read all files first, and then sort them using the qsort function.

The following code demonstrates how to sort directory files using readdir and qsort in Debian system:

 #include<stdio.h>
#include<stdlib.h>
#include<dirent.h>
#include<string.h>

// Custom comparison function for qsort
int compare(const void *a, const void *b) {
    return strcmp(*(const char **)a, *(const char **)b);
}

int main() {
    DIR *dir;
    struct dirent *entry;
    char **filenames = NULL;
    int count = 0;

    // Open the current directory dir = opendir(".");
    if (dir == NULL) {
        perror("opendir");
        return 1; // Return error code}

    // Read directory entry while ((entry = readdir(dir)) != NULL) {
        // Ignore "." and ".."
        if (strcmp(entry->d_name, ".") != 0 && strcmp(entry->d_name, "..") != 0) {
            filenames = realloc(filenames, (count 1) * sizeof(char *));
            if (filenames == NULL) {
                perror("realloc");
                closedir(dir);
                return 1; // Return error code}
            filenames[count] = strdup(entry->d_name); // Use strdup to avoid memory leaks if (filenames[count] == ​​NULL) {
                perror("strdup");
                closedir(dir);
                return 1; // Return error code}
            count ;
        }
    }

    // Close the directory closedir(dir);

    // Use qsort to sort file names qsort(filenames, count, sizeof(char *), compare);

    // Print the sorted file name for (int i = 0; i <p> The improvement of this code is that it uses <code>strdup</code> to copy the file name, avoiding the memory leak problem that may be caused by using <code>strcpy</code> directly; and adding more comprehensive error handling, processing when <code>realloc</code> and <code>strdup</code> fail, freeing the allocated memory, and returning the error code. Finally, remember to free all dynamically allocated memory to avoid memory leaks. This version is more robust and more suitable for practical applications. Note that more complex comparison functions may be required in practical applications to handle different types of file sorting requirements.</p></string.h></dirent.h></stdlib.h></stdio.h>

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