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std::filesy...y::file_size(3)  C++ Standard Libary std::filesy...y::file_size(3)

NAME
     std::filesystem::directory_entry::file_size    -	 std::filesystem::direc-
     tory_entry::file_size

Synopsis
	std::uintmax_t	file_size()   const;				     (1)
     (since C++17)
	std::uintmax_t	file_size(  std::error_code&  ec  )  const noexcept; (2)
     (since C++17)

	If the file size is cached in this directory_entry, returns  the  cached
     value.
	Otherwise, returns:

	1) std::filesystem::file_size(path()),
	2) std::filesystem::file_size(path(), ec).

Parameters
	ec - out-parameter for error reporting in the non-throwing overload

Return value
	The size of the referred-to filesystem object.

Exceptions
	Any  overload not marked noexcept may throw std::bad_alloc if memory al-
     location
	fails.

	1) Throws std::filesystem::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.
	2)  Sets  a std::error_code& parameter to the OS API error code if an OS
     API call
	fails, and executes ec.clear() if no errors occur.

Example
	Prints the list of files in a given directory alongside with their sizes
     in human
	readable form.

     // Run this code

      #include <cmath>
      #include <cstdint>
      #include <filesystem>
      #include <iostream>

      struct HumanReadable
      {
	  std::uintmax_t size{};

	  template<typename Os> friend Os& operator<<(Os& os, HumanReadable hr)
	  {
	      int i{};
	      double mantissa = hr.size;
	      for (; mantissa >= 1024.0; mantissa /= 1024.0, ++i)
	      {}
	      os << std::ceil(mantissa * 10.0) / 10.0 << i["BKMGTPE"];
	      return i ? os << "B (" << hr.size << ')' : os;
	  }
      };

      int main(int argc, const char* argv[])
      {
	  const auto dir = argc == 2 ? std::filesystem::path{argv[1]}
				     : std::filesystem::current_path();

	  for (std::filesystem::directory_entry const& entry :
	       std::filesystem::directory_iterator(dir))
	      if (entry.is_regular_file())
		  std::cout << entry.path().filename() << " size: "
			    << HumanReadable{entry.file_size()} << '\n';
      }

Possible output:
      "boost_1_73_0.tar.bz2" size: 104.2MB (109247910)
      "CppCon 2018 - Jon Kalb aCopy Elisiona.mp4" size: 15.7MB (16411990)
      "cppreference-doc-20190607.tar.xz" size: 6.3MB (6531336)
      "hana.hpp" size: 6.7KB (6807)

See also
	file_size returns the size of a file
	(C++17)   (function)

http://cppreference.com 	   2024.06.10	   std::filesy...y::file_size(3)
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