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

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


std::filesystem::file_size - 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, (1) (since C++17)
std::error_code& ec ) noexcept;

If p does not exist, reports an error.
For a regular file p, returns the size determined as if by reading the st_size member of the structure obtained by POSIX stat (symlinks are followed)
The result of attempting to determine the size of a directory (as well as any other file that is not a regular file or a symlink) is implementation-defined.
The non-throwing overload 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 std::error_code& parameter throws 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.


// 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';

      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

resize_file changes the size of a regular file by truncation or zero-fill

space determines available free space on the file system
            returns the size of the file to which the directory entry refers
file_size (public member function of std::filesystem::directory_entry)