std::filesystem::is_empty
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< cpp | filesystem
C++
Feature test macros (C++20)
Concepts library (C++20)
Metaprogramming library (C++11)
Ranges library (C++20)
Filesystem library (C++17)
Concurrency support library (C++11)
Execution control library (C++26)
Defined in header
<filesystem>
bool is_empty( const std::filesystem::path & p );
(1)
(since C++17)
bool is_empty( const std::filesystem::path & p, std::error_code & ec );
(2)
(since C++17)
Checks whether the given path refers to an empty file or directory.
[edit] Parameters
p
-
path to examine
ec
-
error code to modify in case of error
[edit] Return value
true if the path indicated by p refers to an empty file or directory, false otherwise. The non-throwing overload returns false if an error occurs.
[edit] Exceptions
Any overload not marked noexcept may throw std::bad_alloc if memory allocation fails.
1) Throws std::filesystem::filesystem_error on underlying OS API errors, constructed with p as the first path argument and the OS error code as the error code argument.
2) Sets a std::error_code & parameter to the OS API error code if an OS API call fails, and executes ec.clear () if no errors occur.
[edit] Example
Run this code
#include <cstdio> #include <filesystem> #include <fstream> #include <iostream> int main() { namespace fs = std::filesystem; const fs::path tmp_dir{fs::temp_directory_path()}; std::cout << std::boolalpha << "Temp dir: " << tmp_dir << '\n' << "is_empty(): " << fs::is_empty(tmp_dir) << '\n'; const fs::path tmp_name{tmp_dir / std::tmpnam (nullptr)}; std::cout << "Temp file: " << tmp_name << '\n'; std::ofstream file{tmp_name.string()}; std::cout << "is_empty(): " << fs::is_empty(tmp_name) << '\n'; file << "cppreference.com"; file.flush(); std::cout << "is_empty(): " << fs::is_empty(tmp_name) << '\n' << "file_size(): " << fs::file_size(tmp_name) << '\n'; file.close(); fs::remove(tmp_name); }
Possible output:
Temp dir: "/tmp" is_empty(): false Temp file: "/tmp/fileCqd9DM" is_empty(): true is_empty(): false file_size(): 16
[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 3013 | C++17 | error_code overload marked noexcept but can allocate memory
|
noexcept removed |
[edit] See also
(C++17)(C++17)
determines file attributes, checking the symlink target
(function) [edit]