W3cubDocs

/C++

std::filesystem::file_size

Defined in header <filesystem>
std::uintmax_t file_size( const std::filesystem::path& p );
std::uintmax_t file_size( const std::filesystem::path& p, std::error_code& ec );
(1) (since C++17)

Returns the size of the regular file p, determined as if by reading the st_size member of the structure obtained by POSIX stat (symlinks are followed).

Attempting to determine the size of a directory (as well as any other file that is not a regular file or a symlink) is treated as an error.

The non-throwing overload returns returns -1 on errors.

Parameters

p - path to examine
ec - out-parameter for error reporting in the non-throwing overload

Return value

The size of the file, in bytes.

Exceptions

The overload that does not take a std::error_code& parameter throws filesystem_error on underlying OS API errors, constructed with p as the first argument and the OS error code as the error code argument. std::bad_alloc may be thrown if memory allocation fails. 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. This overload has
noexcept specification:
noexcept

Example

#include <iostream>
#include <fstream>
#include <filesystem>
namespace fs = std::filesystem;
int main()
{
    fs::path p = fs::current_path() / "example.bin";
    std::ofstream(p).put('a'); // create file of size 1
    std::cout << "File size = " << fs::file_size(p) << '\n';
    fs::remove(p);
 
    try {
        fs::file_size("/dev"); // attempt to get size of a directory
    } catch(fs::filesystem_error& e) {
        std::cout << e.what() << '\n';
    }        
}

Possible output:

File size = 1
boost::filesystem::file_size: Operation not permitted: "/dev"

See also

(C++17)
changes the size of a regular file by truncation or zero-fill
(function)
(C++17)
determines available free space on the file system
(function)

© cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.
http://en.cppreference.com/w/cpp/filesystem/file_size