std::filesystem::directory_iterator
| Defined in header <filesystem>
|
||
class directory_iterator; |
(since C++17) | |
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.
Member types
| Member type | Definition |
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 |
Member functions
| constructs a directory iterator (public member function) | |
(destructor) |
default destructor (public member function) |
| assigns contents (public member function) | |
| accesses the pointed-to entry (public member function) | |
| advances to the next entry (public member function) |
Non-member functions
| range-based for loop support (function) |
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.
Helper specializations
template<> constexpr bool ranges::enable_borrowed_range<std::filesystem::directory_iterator> = true; |
(since C++20) | |
template<> constexpr bool ranges::enable_view<std::filesystem::directory_iterator> = true; |
(since C++20) | |
These specializations for directory_iterator make it a borrowed_range and a view.
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.
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"
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 |
See also
(C++17) |
an iterator to the contents of a directory and its subdirectories (class) |
(C++17) |
options for iterating directory contents (enum) |
(C++17) |
a directory entry (class) |