std::filesystem递归目录迭代器权限拒绝：0777目录无法遍历

问题核心 #

使用C++ std::filesystem库递归遍历目录时触发权限错误：

filesystem error: cannot increment recursive directory iterator: Permission denied

程序可进入/dir/和/dir/tmp/，但无法访问dir/tmp/data1，所有目录UID/GID一致，权限显示为0777/0666。

相关信息 #

代码片段 #

auto const dir = std::filesystem::path(...);
std::error_code ec (0, std::generic_category());
try {
    for (auto const& inner_entry : std::filesystem::recursive_directory_iterator(dir, std::filesystem::directory_options::follow_directory_symlink, ec)) {
        std::cout << "Trying to set " << inner_entry.path().c_str() << "to 0666\n";
        try {
            // Code setting permissions on file to 0666
        }
        catch (std::exception const& e) {
            std::cout << "Cannot set " << inner_entry.path().c_str() << "to 0666\n";
        }
    }
} catch (std::exception const& e) {
    std::cout << "Cannot for loop with: " << e.what() << ", " << ec.message();
}

目录结构 #

dir/tmp/data1/
    dir1/
    dir2/
    file1
    file2

stat输出 #

File: /dir
  Size: 1024            Blocks: 2          IO Block: 1024   directory
Device: 706h/1798d      Inode: 1897        Links: 3
Access: (0777/drwxrwxrwx)  Uid: (  default)   Gid: (  default)

  File: /dir/tmp/
  Size: 1024            Blocks: 2          IO Block: 1024   directory
Device: 706h/1798d      Inode: 1899        Links: 3
Access: (0666/drw-rw-rw-)  Uid: (  default)   Gid: (  default)

  File: /dir/tmp/data1
  Size: 1024            Blocks: 2          IO Block: 1024   directory
Device: 706h/1798d      Inode: 1900        Links: 6
Access: (0777/drwxrwxrwx)  Uid: (  default)   Gid: (  default)

程序输出 #

Trying to set dir/ to 0666
Trying to set dir/tmp/ to 0666
Cannot for loop with: filesystem error: cannot increment recursive directory iterator: Permission denied, Success

原因分析 #

1. 目录执行权限缺失：/dir/tmp/权限为0666（drw-rw-rw-），目录的**执行权限（x位）**是进入目录、访问子内容的必要条件——没有x权限，即使有读权限也无法遍历目录内的内容，更无法进入子目录data1。
2. error_code使用错误：范围for循环中，迭代器递增操作出错时会直接抛出异常，不会更新你传入的ec变量，导致捕获异常时ec仍为初始的0值，因此显示"Success"。

修复方案 #

1. 修复目录权限 #

先给/dir/tmp/添加执行权限：

chmod +x /dir/tmp/

目录必须拥有x权限，进程才能进入并访问其内部的文件或子目录。

2. 修正代码的错误处理逻辑 #

改用非抛出式迭代器操作，遇到错误时跳过异常目录，继续遍历：

auto const dir = std::filesystem::path(...);
std::error_code ec;

// 构造迭代器时先检查错误
std::filesystem::recursive_directory_iterator it(dir, std::filesystem::directory_options::follow_directory_symlink, ec);
if (ec) {
    std::cout << "Failed to create iterator: " << ec.message() << "\n";
    return;
}

for (; it != std::filesystem::recursive_directory_iterator(); it.increment(ec)) {
    if (ec) {
        std::cout << "Skip error dir " << it->path() << ": " << ec.message() << "\n";
        ec.clear();
        continue;
    }

    auto const& inner_entry = *it;
    std::cout << "Trying to set " << inner_entry.path().c_str() << " to 0666\n";
    try {
        // 明确设置权限的代码
        std::filesystem::permissions(
            inner_entry.path(),
            std::filesystem::perms::owner_read | std::filesystem::perms::owner_write |
            std::filesystem::perms::group_read | std::filesystem::perms::group_write |
            std::filesystem::perms::others_read | std::filesystem::perms::others_write
        );
    }
    catch (const std::exception& e) {
        std::cout << "Cannot set " << inner_entry.path().c_str() << " to 0666: " << e.what() << "\n";
    }
}

• 使用it.increment(ec)进行非抛出式递增，捕获错误后可跳过异常目录继续遍历。
• 构造迭代器时直接检查错误，避免后续异常。
• 补全权限设置的具体代码，替换原注释部分。

内容的提问来源于stack exchange，提问作者aaa