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std::basic_filebuf::setbuf(3)  C++ Standard Libary std::basic_filebuf::setbuf(3)

NAME
     std::basic_filebuf::setbuf - std::basic_filebuf::setbuf

Synopsis
	protected:
	virtual   std::basic_streambuf<CharT,  Traits>*  setbuf(  char_type*  s,
     std::streamsize
	n )

	If s is a null pointer and n is zero, the filebuf becomes unbuffered for
     output,
	meaning pbase() and pptr() are null and any output is  immediately  sent
     to file.

	Otherwise,  a  call  to  setbuf() replaces the internal buffer (the con-
     trolled character
	sequence) with the user-supplied character array whose first element  is
     pointed to
	by  s  and allows this std::basic_filebuf object to use up to n bytes in
     that array
	for buffering.

	This function is protected virtual, it may only be called  through  pub-
     setbuf() or
	from  member  functions  of  a	user-defined class derived from std::ba-
     sic_filebuf.

Parameters
	s - pointer to the first CharT in the user-provided buffer or null
	n - the number of CharT elements in the user-provided buffer or zero

Return value
	this

Notes
	The conditions when this function may be used and the way in  which  the
     provided
	buffer is used is implementation-defined.

	  * GCC 4.6 libstdc++

	setbuf()  may  only be called when the std::basic_filebuf is not associ-
     ated with a
	file (has no effect otherwise). With  a  user-provided	buffer,  reading
     from file reads
	n-1 bytes at a time.
	  * Clang++3.0 libc++

	setbuf()  may  be called after opening the file, but before any I/O (may
     crash
	otherwise). With a user-provided buffer, reading from file reads largest
     multiples
	of 4096 that fit in the buffer.
	  * Visual Studio 2010

	setbuf() may be called at any time, even after some I/O took place. Cur-
     rent contents
	of the buffer, if any, are lost.

	The standard does not define any behavior for this function except  that
     setbuf(0, 0)
	called before any I/O has taken place is required to set unbuffered out-
     put.

Example
	Provides  a  10k buffer for reading. On linux, the strace utility may be
     used to
	observe the actual number of bytes read.

     // Run this code

      #include <fstream>
      #include <iostream>
      #include <string>

      int main()
      {
	  int cnt = 0;
	  std::ifstream file;
	  char buf[10241];

	  file.rdbuf()->pubsetbuf(buf, sizeof buf);
	  file.open("/usr/share/dict/words");

	  for (std::string line; getline(file, line);)
	      ++cnt;
	  std::cout << cnt << '\n';
      }

Possible output:
      356010

	Defect reports

	The following behavior-changing defect	reports  were  applied	retroac-
     tively to
	previously published C++ standards.

	  DR	 Applied  to	     Behavior as published		 Correct
     behavior
	LWG 173 C++98	   the type of n was  misspecified  as	   corrected  to
     std::streamsize
			   int

See also
	pubsetbuf invokes setbuf()
		  (public member function of std::basic_streambuf<CharT,Traits>)
	setvbuf   sets the buffer and its size for a file stream
		  (function)

http://cppreference.com 	   2024.06.10	   std::basic_filebuf::setbuf(3)
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