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std::experi...resize_file(3)   C++ Standard Libary  std::experi...resize_file(3)

NAME
     std::experimental::filesystem::resize_file   -  std::experimental::filesys-
     tem::resize_file

Synopsis
	Defined in header <experimental/filesystem>
	void resize_file( const path& p, std::uintmax_t new_size );
	void   resize_file(   const   path&    p,    std::uintmax_t    new_size,
     (filesystem TS)
	error_code& ec );

	Changes the size of the regular file named by p as if by POSIX truncate:
     if the file
	size  was  previously larger than new_size, the remainder of the file is
     discarded. If
	the file was previously smaller than new_size,	the  file  size  is  in-
     creased and the
	new area appears as if zero-filled.

Parameters
	p	 - path to resize
	new_size - size that the file will now have
	ec	  -  out-parameter for error reporting in the non-throwing over-
     load

Return value
	(none)

Exceptions
	The overload that does not take an error_code& parameter throws filesys-
     tem_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 an 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

Notes
	On systems that support sparse files, increasing the file size does  not
     increase the
	space  it occupies on the file system: space allocation takes place only
     when
	non-zero bytes are written to the file.

Example
	Demonstrates the effect of creating a sparse file on the free space.

     // Run this code

      #include <experimental/filesystem>
      #include <fstream>
      #include <iostream>
      namespace fs = std::experimental::filesystem;

      int main()
      {
	  fs::path p = fs::temp_directory_path() / "example.bin";
	  std::ofstream(p).put('a');
	  std::cout << "File size:  " << fs::file_size(p) << '\n'
		    << "Free space: " << fs::space(p).free << '\n';
	  fs::resize_file(p, 64*1024); // resize to 64 KB
	  std::cout << "File size:  " << fs::file_size(p) << '\n'
		    << "Free space: " << fs::space(p).free << '\n';
	  fs::remove(p);
      }

Possible output:
      File size:  1
      Free space: 31805444096
      File size:  65536
      Free space: 31805444096

See also
	file_size returns the size of a file
		  (function)
	space	  determines available free space on the file system
		  (function)

Categories:
	  * Noindexed pages
	  * unconditionally noexcept

Hidden categories:
	  * Pages with unreviewed unconditional noexcept template
	  * Pages with unreviewed noexcept template

http://cppreference.com 	   2024.06.10	    std::experi...resize_file(3)
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