std::experimental::filesystem::file_size (3) - Linux Manuals

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

Command to display std::experimental::filesystem::file_size manual in Linux: $ man 3 std::experimental::filesystem::file_size

NAME

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]