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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 file-
     name.

	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  automati-
     cally 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 occurred.

Notes
	On some implementations (e.g. older Linux), this function actually  cre-
     ates, 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  termi-
     nates
	(normally or abnormally), the space occupied by the file is reclaimed by
     the
	filesystem.  Newer  Linux (since 3.11 or later, depending on filesystem)
     creates such
	invisible temporary files in one step, via special flag  in  the  open()
     syscall.

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

Example
     // Run this code

      #include <cstdio>
      #include <cstdlib>
      #include <filesystem>
      #include <iostream>
      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)
	C documentation for
	tmpfile

http://cppreference.com 	   2024.06.10			 std::tmpfile(3)
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