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std::filesystem::directory_iterator

From cppreference.com
 
 
 
 
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.

Contents

[edit] 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

[edit] Member functions

constructs a directory iterator
(public member function) [edit]
(destructor)
default destructor
(public member function) [edit]
assigns contents
(public member function) [edit]
accesses the pointed-to entry
(public member function) [edit]
advances to the next entry
(public member function) [edit]

[edit] Non-member functions

range-based for loop support
(function) [edit]

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 templates

namespace std::ranges {

template<>
inline constexpr bool
    enable_borrowed_range<std::filesystem::directory_iterator> = true;

}
(since C++20)
namespace std::ranges {

template<>
inline constexpr bool enable_view<std::filesystem::directory_iterator> = true;

}
(since C++20)

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

[edit] See also

an iterator to the contents of a directory and its subdirectories
(class) [edit]
options for iterating directory contents
(enum) [edit]
a directory entry
(class) [edit]