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

FreeBSD Manual Pages

  
 
  

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

NAME
       std::tmpfile - std::tmpfile

Synopsis
	  Defined in header <cstdio>
	  std::FILE* tmpfile();

	  Creates  and	opens  a  temporary  file with a unique	auto-generated
       filename.

	  The file is opened as	a binary file for  update  (as	by  std::fopen
       with access mode
	  "wb+").  At least TMP_MAX files may be opened	during the lifetime of
       a program (this
	  limit	may be shared with std::tmpnam and may be further  limited  by
       FOPEN_MAX).

	  If  the  program closes the file, e.g. by executing std::fclose, the
       file is
	  automatically	deleted.

	  If the program terminates normally (by calling std::exit,  returning
       from main, etc),
	  all files that were opened by	calling	std::tmpfile are also automat-
       ically deleted.

	  If  the  program terminates abnormally, it is	implementation-defined
       if these
	  temporary files are deleted.

Parameters
	  (none)

Return value
	  The associated file stream or	a null pointer if  an  error  has  oc-
       curred

Notes
	  On  some  implementations (e.g. older	Linux),	this function actually
       creates,	opens,
	  and immediately deletes the file from	the file system: as long as an
       open file
	  descriptor to	a deleted file is held by a program, the file  exists,
       but since it was
	  deleted, its name does not appear in any directory, so that no other
       process can
	  open	it.  Once  the	file descriptor	is closed, or once the program
       terminates
	  (normally or abnormally), the	space occupied	by  the	 file  is  re-
       claimed by the
	  filesystem.  Newer Linux (since 3.11 or later, depending on filesys-
       tem) creates such
	  invisible temporary files in one  step,  via	special	 flag  in  the
       open() syscall.

	  On  some implementations (e.g. Windows), elevated privileges are re-
       quired as the
	  function may create the temporary file in a system directory.

Example
       // Run this code

	#include <iostream>
	#include <cstdio>
	#include <cstdlib>
	#include <filesystem>
	namespace fs = std::filesystem;

	int main()
	{
	    std::cout << "TMP_MAX = " << TMP_MAX << '\n'
		      << "FOPEN_MAX = "	<< FOPEN_MAX <<	'\n';
	    std::FILE* tmpf = std::tmpfile();
	    std::fputs("Hello, world", tmpf);
	    std::rewind(tmpf);
	    char buf[6];
	    std::fgets(buf, sizeof buf,	tmpf);
	    std::cout << buf <<	'\n';

	    // Linux-specific method to	display	the tmpfile name
	    std::cout << fs::read_symlink(
			     fs::path("/proc/self/fd")			     /
       std::to_string(fileno(tmpf))
			 ) << '\n';
	}

Possible output:
	TMP_MAX	= 238328
	FOPEN_MAX = 16
	Hello
	"/tmp/tmpfBlY1lI (deleted)"

See also
	  tmpnam	      returns a	unique filename
			      (function)
	  temp_directory_path returns a	directory suitable for temporary files
	  (C++17)	      (function)

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

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

home | help