std::filesystem::directory_iterator
<filesystem>
directory_iterator is a LegacyInputIterator that iterates over the directory_entry elements of a directory (but does not visit the subdirectories). The iteration order is unspecified, except that each directory entry is visited only once. The special pathnames dot and dot-dot are skipped.
If the directory_iterator reports an error or is advanced past the last directory entry, 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 directory iterator has been created, it is unspecified whether the change would be observed through the iterator.
Contents
[edit] Member types
value_type
std::filesystem::directory_entry
difference_type
std::ptrdiff_t
pointer
const std::filesystem::directory_entry *
reference
const std::filesystem::directory_entry &
iterator_category
std::input_iterator_tag
[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
constexpr bool
constexpr bool
These specializations for directory_iterator make it a borrowed_range and a view.
[edit] Notes
Many low-level OS APIs for directory traversal retrieve file attributes along with the next directory entry. The constructors and the non-const member functions of std::filesystem::directory_iterator store these attributes, if any, in the pointed-to std::filesystem::directory_entry without calling directory_entry::refresh, which makes it possible to examine the attributes of the directory entries as they are being iterated over, without making additional system calls.
[edit] Example
#include <algorithm> #include <filesystem> #include <fstream> #include <iostream> int main() { const std::filesystem::path sandbox{"sandbox"}; std::filesystem::create_directories (sandbox/"dir1"/"dir2"); std::ofstream {sandbox/"file1.txt"}; std::ofstream {sandbox/"file2.txt"}; std::cout << "directory_iterator:\n"; // directory_iterator can be iterated using a range-for loop for (auto const& dir_entry : std::filesystem::directory_iterator{sandbox}) std::cout << dir_entry.path() << '\n'; std::cout << "\ndirectory_iterator as a range:\n"; // directory_iterator behaves as a range in other ways, too std::ranges::for_each ( std::filesystem::directory_iterator{sandbox}, [](const auto& dir_entry) { std::cout << dir_entry << '\n'; }); std::cout << "\nrecursive_directory_iterator:\n"; for (auto const& dir_entry : std::filesystem::recursive_directory_iterator {sandbox}) std::cout << dir_entry << '\n'; // delete the sandbox dir and all contents within it, including subdirs std::filesystem::remove_all (sandbox); }
Possible output:
directory_iterator: "sandbox/file2.txt" "sandbox/file1.txt" "sandbox/dir1" directory_iterator as a range: "sandbox/file2.txt" "sandbox/file1.txt" "sandbox/dir1" recursive_directory_iterator: "sandbox/file2.txt" "sandbox/file1.txt" "sandbox/dir1" "sandbox/dir1/dir2"
[edit] Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 3480 | C++20 | directory_iterator was neither a borrowed_range nor a view
|
it is both |