How do I iterate over multiple directories in one loop?

Question

Ryan McCombe · Accepted Answer

Iterating over multiple directories in one loop can be accomplished by initializing iterators for each directory and processing them in sequence.

You can use a container to store the directory paths and loop through each path with a std::filesystem::directory_iterator.

Here's an example that iterates over multiple directories:

1#include <filesystem>
2#include <iostream>
3#include <vector>
4
5namespace fs = std::filesystem;
6
7int main() {
8  std::vector<fs::path> directories{
9    R"(c:\test1)", R"(c:\test2)", R"(c:\test3)"};  
10
11  for (const auto& dir : directories) {
12    std::cout << "Directory: " << dir.string() << '\n';
13    fs::directory_iterator start{dir};
14    fs::directory_iterator end{};
15
16    for (auto iter{start}; iter != end; ++iter) {
17      std::cout << iter->path().string() << '\n';
18    }
19  }
20}

1Directory: c:\test1
2c:\test1\file1.txt
3c:\test1\file2.txt
4Directory: c:\test2
5c:\test2\fileA.txt
6c:\test2\fileB.txt
7Directory: c:\test3
8c:\test3\fileX.txt
9c:\test3\fileY.txt

Steps to Iterate Multiple Directories:

List Directories: Create a container (e.g., std::vector<fs::path>) to store the directory paths.
Loop Through Directories: Use a loop to iterate over each directory path.
Initialize and Iterate: For each directory, initialize a std::filesystem::directory_iterator and process the entries.

Using a Recursive Approach:

If you need to handle nested directories, consider a recursive function:

1#include <filesystem>
2#include <iostream>
3
4namespace fs = std::filesystem;
5
6void process_directory(const fs::path& dir) {
7  std::cout << "Directory: " << dir.string() << '\n';
8  fs::directory_iterator start{dir};
9  fs::directory_iterator end{};
10
11  for (auto iter{start}; iter != end; ++iter) {
12    if (iter->is_directory()) {
13      // Recurse into subdirectory
14      process_directory(iter->path());  
15    } else {
16      std::cout << iter->path().string() << '\n';
17    }
18  }
19}
20
21int main() {
22  std::vector<fs::path> directories{
23    R"(c:\test1)", R"(c:\test2)", R"(c:\test3)"};
24
25  for (const auto& dir : directories) {
26    process_directory(dir);  
27  }
28}

1Directory: c:\test1
2c:\test1\file1.txt
3c:\test1\file2.txt
4Directory: c:\test2
5c:\test2\fileA.txt
6c:\test2\fileB.txt
7Directory: c:\test3
8c:\test3\fileX.txt
9c:\test3\fileY.txt

Using a Queue for Iteration:

For a non-recursive approach, use a queue to manage directories:

1#include <filesystem>
2#include <iostream>
3#include <queue>
4
5namespace fs = std::filesystem;
6
7int main() {
8  std::queue<fs::path> dirs;
9  dirs.push(R"(c:\test1)");
10  dirs.push(R"(c:\test2)");
11  dirs.push(R"(c:\test3)");
12
13  while (!dirs.empty()) {
14    auto dir = dirs.front();
15    dirs.pop();
16    std::cout << "Directory: " << dir.string() << '\n';
17
18    fs::directory_iterator start{dir};
19    fs::directory_iterator end{};
20
21    for (auto iter{start}; iter != end; ++iter) {
22      std::cout << iter->path().string() << '\n';
23      if (iter->is_directory()) {
24        // Add subdirectory to queue
25        dirs.push(iter->path());  
26      }
27    }
28  }
29}

1Directory: c:\test1
2c:\test1\file1.txt
3c:\test1\file2.txt
4Directory: c:\test2
5c:\test2\fileA.txt
6c:\test2\fileB.txt
7Directory: c:\test3
8c:\test3\fileX.txt
9c:\test3\fileY.txt

These techniques allow you to iterate over multiple directories efficiently, processing their contents as needed. Whether using simple loops, recursion, or a queue, you can handle complex directory structures with ease.

Directory Iterators

Iterate Multiple Directories

Steps to Iterate Multiple Directories:

Using a Recursive Approach:

Using a Queue for Iteration:

Directory Iterators

Professional C++

Questions & Answers