Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages

  
 
  

home | help 
std::freopen(3)		      C++ Standard Libary	       std::freopen(3)

NAME
       std::freopen - std::freopen

Synopsis
	  Defined in header <cstdio>
	  std::FILE*   freopen(	  const	 char*	filename,  const  char*	 mode,
       std::FILE* stream );

	  First, attempts to close the file associated with  stream,  ignoring
       any errors. Then,
	  if  filename	is  not	 null,	attempts to open the file specified by
       filename	using mode
	  as if	by std::fopen, and associates that file	with the  file	stream
       pointed to by
	  stream. If filename is a null	pointer, then the function attempts to
       reopen the file
	  that is already associated with stream (it is	implementation defined
       which mode
	  changes are allowed in this case).

Parameters
	  filename - file name to associate the	file stream to
	  mode	   - null-terminated character string determining new file ac-
       cess mode
	  stream   - the file stream to	modify

	 File access flags

	   File	 access	       Meaning	       Explanation	Action if file
       Action if file
	   mode	string					       already	exists
       does not	exist
	  "r"		  read		    Open a file	for    read from start
       return NULL and
					   reading
       set error
	  "w"		 write		   Create a file for  destroy contents
       create new
					   writing
	  "a"		 append		   Append to a	file	write  to  end
       create new
	  "r+"		  read extended	    Open a file	for    read from start
       return NULL and
					   read/write
       set error
	  "w+"		 write extended	   Create a file for  destroy contents
       create new
					   read/write
	  "a+"		 append	extended   Open	a file	for	write  to  end
       create new
					   read/write
	  File access mode flag	"b" can	optionally be specified	to open	a file
       in binary mode.
	  This	flag has no effect on POSIX systems, but on Windows, for exam-
       ple, it disables
	  special handling of '\n' and '\x1A'.
	  On the append	file access modes, data	is written to the end  of  the
       file regardless
	  of the current position of the file position indicator.
	  File	access mode flag "x" can optionally be appended	to "w" or "w+"
       specifiers. This
	  flag forces the function to fail if  the  file  exists,  instead  of
       overwriting it.
	  (C++17)
	  The  behavior	 is  undefined	if  the	mode is	not one	of the strings
       listed above. Some
	  implementations define additional supported modes (e.g. Windows).

Return value
	  stream on success, a null pointer on failure

Notes
	  std::freopen is the only way to change the  narrow/wide  orientation
       of a stream once
	  it has been established by an	I/O operation or by std::fwide.

	  Microsoft  CRT  version  of  std::freopen  does not support any mode
       changes when
	  filename is a	null pointer and treats	this as	an error (see documen-
       tation).	A
	  possible workaround is the non-standard function _setmode().

Example
	  The following	code redirects stdout to a file

       // Run this code

	#include <cstdio>

	int main()
	{
	    std::printf("stdout	is printed to console\n");
	    if(std::freopen("redir.txt", "w", stdout)) {
		std::printf("stdout is redirected to a file\n");  //  this  is
       written to redir.txt
		std::fclose(stdout);
	    }
	}

Output:
	stdout is printed to console

See also
	  fopen	 opens a file
		 (function)
	  fclose closes	a file
		 (function)

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

Want to link to this manual page? Use this URL:
<https://man.freebsd.org/cgi/man.cgi?query=std::freopen&sektion=3&manpath=FreeBSD+Ports+15.0>

home | help