Difference between revisions of "cpp/filesystem/recursive directory iterator"

Latest revision as of 19:36, 30 October 2024

recursive_directory_iterator is a LegacyInputIterator that iterates over the directory_entry elements of a directory, and, recursively, over the entries of all subdirectories. The iteration order is unspecified, except that each directory entry is visited only once.

By default, symlinks are not followed, but this can be enabled by specifying the directory option follow_directory_symlink at construction time.

The special pathnames dot and dot-dot are skipped.

If the recursive_directory_iterator reports an error or is advanced past the last directory entry of the top-level directory, it becomes equal to the default-constructed iterator, also known as the end iterator. Two end iterators are always equal, dereferencing or incrementing the end iterator is undefined behavior.

If a file or a directory is deleted or added to the directory tree after the recursive directory iterator has been created, it is unspecified whether the change would be observed through the iterator.

If the directory structure contains cycles, the end iterator may be unreachable.

[edit] Member types

[edit] Member functions

[edit] Non-member functions

Additionally, operator== and operator!= are(until C++20)operator== is(since C++20) provided as required by LegacyInputIterator.

It is unspecified whether operator!= is provided because it can be synthesized from operator==, and(since C++20) whether an equality operator is a member or non-member.

[edit] Helper specializations

These specializations for recursive_directory_iterator make it a borrowed_range and a view.

[edit] Notes

A recursive_directory_iterator typically holds a reference-counted pointer (to satisfy shallow-copy semantics of LegacyInputIterator) to an implementation object, which holds:

• a container (such as std::vector) of non-recursive directory_iterators that forms the recursion stack,
• the recursion depth counter (accessible with depth()),
• the directory options used at construction (accessible with options()),
• the pending recursion flag (accessible with recursion_pending(), may be combined with the directory options to save space).

[edit] Example

#include <filesystem>
#include <fstream>
#include <iostream>
#include <string>
namespace fs = std::filesystem;
 
int main()
{
    std::filesystem::current_path(std::filesystem::temp_directory_path());
    std::filesystem::create_directories("sandbox/a/b");
    std::ofstream("sandbox/file1.txt");
    std::filesystem::create_symlink("a", "sandbox/syma");
 
    // Iterate over the std::filesystem::directory_entry elements explicitly
    auto entry_length{3UZ};
    for (const fs::directory_entry& dir_entry :
            fs::recursive_directory_iterator("sandbox"))
    {
        std::cout << dir_entry << '\n';
        if (auto l{dir_entry.path().string().length()}; entry_length < l)
            entry_length = l;
    }
    std::cout << std::string(entry_length + 2, '-') << '\n';
 
    // Iterate over the std::filesystem::directory_entry elements using `auto`
    for (auto const& dir_entry : fs::recursive_directory_iterator("sandbox"))
        std::cout << dir_entry << '\n';
 
    std::filesystem::remove_all("sandbox");
}

"sandbox/syma"
"sandbox/file1.txt"
"sandbox/a"
"sandbox/a/b"
-------------------
"sandbox/syma"
"sandbox/file1.txt"
"sandbox/a"
"sandbox/a/b"

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

[edit] See also