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std::fseek(3)		      C++ Standard Libary		 std::fseek(3)

NAME
       std::fseek - std::fseek

Synopsis
	  Defined in header <cstdio>
	  int fseek( std::FILE*	stream,	long offset, int origin	);

	  Sets the file	position indicator for the file	stream stream.

	  If  the  stream  is open in binary mode, the new position is exactly
       offset bytes
	  measured from	the beginning of the file if origin is SEEK_SET,  from
       the current file
	  position if origin is	SEEK_CUR, and from the end of the file if ori-
       gin is SEEK_END.
	  Binary  streams  are not required to support SEEK_END, in particular
       if additional
	  null bytes are output.

	  If the stream	is open	in text	mode, the only	supported  values  for
       offset are zero
	  (which  works	 with  any  origin) and	a value	returned by an earlier
       call to std::ftell
	  on a stream associated with the same file  (which  only  works  with
       origin of
	  SEEK_SET).

	  If  the  stream  is wide-oriented, the restrictions of both text and
       binary streams
	  apply	(result	of std::ftell is allowed with SEEK_SET and zero	offset
       is allowed from
	  SEEK_SET and SEEK_CUR, but not SEEK_END)

	  In addition to changing the file position  indicator,	 fseek	undoes
       the effects of
	  std::ungetc and clears the end-of-file status, if applicable.

	  If  a	read or	write error occurs, the	error indicator	for the	stream
       (std::ferror) is
	  set and the file position is unaffected.

Parameters
	  stream - file	stream to modify
	  offset - number of characters	to shift the position relative to ori-
       gin
	  origin - position to which offset is added. It can have one  of  the
       following values:
		   SEEK_SET, SEEK_CUR, SEEK_END

Return value
	  0 upon success, nonzero value	otherwise.

Notes
	  After	 seeking to a non-end position in a wide stream, the next call
       to any output
	  function may render the remainder of the  file  undefined,  e.g.  by
       outputting a
	  multibyte sequence of	a different length.

	  POSIX	 allows	 seeking beyond	the existing end of file. If an	output
       is performed
	  after	this seek, any read from the gap will return zero bytes. Where
       supported by
	  the filesystem, this creates a sparse	file.

	  POSIX	also requires that fseek first performs	fflush	if  there  are
       any unwritten data
	  (but whether the shift state is restored is implementation-defined).
       The standard
	  C++  file  streams  guarantee	both flushing and unshifting: std::ba-
       sic_filebuf::seekoff

Example
       // Run this code

	#include <cstdio>
	#include <cstdint>
	#include <vector>
	#include <fstream>
	#include <cassert>

	int main()
	{
	    std::ofstream("dummy.nfo") << "sample data\n";

	    std::FILE* fp = std::fopen("dummy.nfo", "rb");
	    assert(fp);

	    std::fseek(fp, 0, SEEK_END); // seek to end
	    std::size_t	filesize = std::ftell(fp);

	    std::fseek(fp, 0, SEEK_SET); // seek to start
	    std::vector<uint8_t> buffer(filesize);
	    std::fread(buffer.data(), sizeof(uint8_t), buffer.size(), fp);

	    std::fclose(fp);
	    std::printf("i've read %zi bytes\n", filesize);
	}

Output:
	i've read 12 bytes

See also
	  fsetpos moves	the file position indicator to a specific location  in
       a file
		  (function)
	  fgetpos gets the file	position indicator
		  (function)
	  ftell	  returns the current file position indicator
		  (function)
	  rewind  moves	the file position indicator to the beginning in	a file
		  (function)

http://cppreference.com		  2022.07.31			 std::fseek(3)

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