How can I stop the iteration prematurely when using `directory_iterator`?

Question

Ryan McCombe · Accepted Answer

You can stop the iteration prematurely by using the break statement within your loop. This allows you to exit the loop based on a specific condition or requirement.

Here's an example where we stop the iteration after finding a specific file:

1#include <filesystem>
2#include <iostream>
3
4namespace fs = std::filesystem;
5
6int main() {
7  fs::directory_iterator start{R"(c:\test)"};
8  fs::directory_iterator end{};
9
10  for (auto iter{start}; iter != end; ++iter) {
11    std::cout << iter->path().string() << '\n';
12    if (iter->path().filename() == "stop_here.txt") {
13      break; // Stop iteration  
14    }
15  }
16}

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

Common Use Cases for Stopping Early:

Finding a Specific File or Directory: Stop once a specific entry is found.
Resource Limits: Stop if a certain resource limit is reached (e.g., memory usage, number of processed files).
User Input: Allow the user to interrupt the process based on input or an external event.

Example: Stopping Based on File Count:

Here's another example where we stop after processing a certain number of files:

1#include <filesystem>
2#include <iostream>
3
4namespace fs = std::filesystem;
5
6int main() {
7  fs::directory_iterator start{R"(c:\test)"};
8  fs::directory_iterator end{};
9
10  int count = 0;
11  // Maximum files to process
12  const int max_files = 5;  
13
14  for (auto iter{start}; iter != end; ++iter) {
15    if (count >= max_files) {  
16      break; // Stop after processing max_files  
17    }
18    std::cout << iter->path().string() << '\n';
19    ++count;
20  }
21}

1c:\test\file1.txt
2c:\test\file2.txt
3c:\test\file3.txt
4c:\test\file4.txt
5c:\test\file5.txt

Handling Complex Conditions:

For more complex conditions, you can combine multiple checks:

1#include <filesystem>
2#include <iostream>
3
4namespace fs = std::filesystem;
5
6bool should_stop(const fs::directory_entry& entry) {
7  // Example condition: stop at specific file
8  // or if file size exceeds limit
9  return entry.path().filename() == "stop_here.txt"
10    || entry.is_regular_file()
11    && entry.file_size() > 1024;  
12}
13
14int main() {
15  fs::directory_iterator start{R"(c:\test)"};
16  fs::directory_iterator end{};
17
18  for (auto iter{start}; iter != end; ++iter) {
19    if (should_stop(*iter)) {
20      break;  
21    }
22    std::cout << iter->path().string() << '\n';
23  }
24}

1c:\test\file1.txt
2c:\test\file2.txt
3c:\test\file3.txt

Stopping the iteration prematurely is a straightforward process in C++. Use conditions and the break statement to control the flow of your directory traversal as needed.

Directory Iterators

Stop Directory Iteration Early

Common Use Cases for Stopping Early:

Example: Stopping Based on File Count:

Handling Complex Conditions:

Directory Iterators

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