Sort Directory Entries

While std::filesystem::directory_iterator does not directly support sorting, you can collect the directory entries into a container (like std::vector), sort the container, and then iterate over it.

Here’s an example of how to sort directory entries by their file names:

1#include <filesystem>
2#include <iostream>
3#include <vector>
4#include <algorithm>
5
6namespace fs = std::filesystem;
7
8int main() {
9  fs::directory_iterator start{R"(c:\test)"};
10  fs::directory_iterator end{};
11
12  std::vector<fs::directory_entry> entries; 
13  for (auto iter{start}; iter != end; ++iter) {
14    entries.push_back(*iter);
15  }
16
17  std::sort(entries.begin(), entries.end(), 
18    [](const fs::directory_entry& a,
19      const fs::directory_entry& b) {
20      return a.path().filename()
21        < b.path().filename(); 
22  });
23
24  for (const auto& entry : entries) {
25    std::cout << entry.path().string() << '\n';
26  }
27}

1c:\test\another_directory
2c:\test\file1.txt
3c:\test\file2.txt

Steps to Sort Entries:

1. Collect Entries: Use a loop to gather directory entries into a container like std::vector.
2. Sort Container: Use std::sort() with a custom comparator to sort the entries based on desired criteria (e.g., filename).
3. Iterate Sorted Container: Iterate over the sorted container and process the entries.

Sorting by Different Criteria:

You can sort by other criteria, such as file size or modification time:

1std::sort(entries.begin(), entries.end(),
2  [](const fs::directory_entry& a,
3     const fs::directory_entry& b) {
4    return fs::file_size(a) < fs::file_size(b); 
5  });

Using Range-Based Algorithms:

You can also leverage std::ranges for a more modern approach:

1#include <filesystem>
2#include <iostream>
3#include <vector>
4#include <ranges>
5
6namespace fs = std::filesystem;
7
8int main() {
9  auto entries = std::ranges::subrange{
10    fs::directory_iterator{R"(c:\test)"},
11    fs::directory_iterator{}
12  } | std::ranges::to<std::vector>();
13
14  std::ranges::sort(
15    entries, {}, &fs::directory_entry::path);
16
17  for (const auto& entry : entries) {
18    std::cout << entry.path().string() << '\n';
19  }
20}

Sorting directory entries provides greater flexibility and control over how you process files and directories. By collecting entries into a container and sorting them, you can achieve any custom order needed for your application.