Std::experimental::filesystem::file_size (3) Linux Manual Page

std::experimental::filesystem::file_size – std::experimental::filesystem::file_size

Synopsis

Defined in header<experimental / filesystem>

    std::uintmax_t file_size(const path &p);
(1)(filesystem TS)

    std::uintmax_t file_size(const path &p, error_code &ec);

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 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:
noexcept

Example

// Run this code

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

std::experimental::filesystem::file_size (3) Linux Manual Page