< cpp‎ | experimental‎ | fs
Technical specifications
Filesystem library (filesystem TS)
Library fundamentals (library fundamentals TS)
Library fundamentals 2 (library fundamentals 2 TS)
Extensions for parallelism (parallelism TS)
Extensions for parallelism 2 (parallelism TS v2)
Extensions for concurrency (concurrency TS)
Concepts (concepts TS)
Ranges (ranges TS)
Special mathematical functions (special math TR)
Defined in header <experimental/filesystem>
std::uintmax_t file_size( const path& p );
std::uintmax_t file_size( const path& p, error_code& ec );
(1) (filesystem TS)

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.


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

Return value

The size of the file, in bytes.


The overload that does not take a 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 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:  


#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';
    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
filesystem error: cannot get file size: Is a directory [/dev]

See also

changes the size of a regular file by truncation or zero-fill
determines available free space on the file system