identifier "directory_iterator" is undefined

The "directory_iterator" identifier is used in C++ to iterate over the contents of a directory. This feature is available in the Standard Library starting from C++17. To use it, you need to include the <filesystem> header and use the std::filesystem namespace.

Here's an example of how to use directory_iterator:

#include <iostream>
#include <filesystem>

namespace fs = std::filesystem;

int main() {
    fs::path directoryPath = "path/to/directory";

    for (const auto& entry : fs::directory_iterator(directoryPath)) {
        std::cout << entry.path() << std::endl;
    }

    return 0;
}

Make sure your compiler supports C++17 or later, and you have included the <filesystem> header.