查找进程linux(C代码)的打开文件描述符？

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

void list_fds(pid_t pid) {
    char path[256];
    snprintf(path, sizeof(path), "/proc/%d/fd", pid);

    DIR *dir = opendir(path);
    if (!dir) {
        perror("opendir");
        return;
    }

    struct dirent *entry;
    while ((entry = readdir(dir)) != NULL) {
        if (entry->d_name[0] == '.') {
            continue;
        }

        snprintf(path, sizeof(path), "/proc/%d/fd/%s", pid, entry->d_name);
        char link[256];
        ssize_t len = readlink(path, link, sizeof(link) - 1);
        if (len < 0) {
            perror("readlink");
            continue;
        }

        link[len] = '\0';
        printf("fd %s -> %s\n", entry->d_name, link);
    }

    closedir(dir);
}

int main(int argc, char *argv[]) {
    pid_t pid;
    if (argc == 2) {
        pid = atoi(argv[1]);
    } else {
        pid = getpid();
    }

    printf("Listing file descriptors for process %d:\n", pid);
    list_fds(pid);

    return 0;
}

./list_fds 12345