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std::filesystem::is_empty

From cppreference.com
 
 
 
Defined in header <filesystem>
bool is_empty( const std::filesystem::path& p );
bool is_empty( const std::filesystem::path& p, std::error_code& ec );
(since C++17)

Checks whether the given path refers to an empty file or directory.

Contents

[edit] Parameters

p - path to examine
ec - error code to modify in case of error

[edit] Return value

true if the file indicated by p or if the type indicated s refers to an empty file or directory, false otherwise. The non-throwing overload returns false if an error occurs.

[edit] Exceptions

The overload that does not take a std::error_code& parameter throws 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. The overload taking a std::error_code& parameter sets it to the OS API error code if an OS API call fails, and executes ec.clear() if no errors occur. Any overload not marked noexcept may throw std::bad_alloc if memory allocation fails.

[edit] Example

#include <filesystem>
#include <fstream>
#include <iostream>
#include <cstdio>
 
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
determines file attributes, checking the symlink target
(function) [edit]
(C++17)
checks whether path refers to existing file system object
(function) [edit]