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

NAME
     std::fopen - std::fopen

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

	Opens  a file indicated by filename and returns a file stream associated
     with that
	file. mode is used to determine the file access mode.

Parameters
	filename - file name to associate the file stream to
	mode	 - null-terminated character string determining file access mode

	File access flags

	 File access	    Meaning	    Explanation      Action if file  Ac-
     tion if file
	 mode  string						already   exists
     does not exist
	"r"	       read		 Open a file for    read from start  re-
     turn 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  re-
     turn 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	example,
     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 over-
     writing 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
	If  successful, returns a pointer to the object that controls the opened
     file stream,
	with both eof and error bits cleared. The stream is fully  buffered  un-
     less filename
	refers to an interactive device.

	On  error,  returns  a null pointer. POSIX requires that errno is set in
     this case.

Notes
	The format of filename is implementation-defined, and does not necessar-
     ily refer to
	a file (e.g. it may be the console or another device accessible  through
     filesystem
	API).  On  platforms that support them, filename may include absolute or
     relative
	filesystem path.

	For portable directory and file naming, see C++ filesystem library or
	boost.filesystem.

Example
     // Run this code

      #include <cstdio>
      #include <cstdlib>

      int main()
      {
	  int is_ok = EXIT_FAILURE;
	  FILE* fp = std::fopen("/tmp/test.txt", "w+");
	  if (!fp)
	  {
	      std::perror("File opening failed");
	      return is_ok;
	  }

	  int c; // Note: int, not char, required to handle EOF
	  while ((c = std::fgetc(fp)) != EOF) // Standard  C  I/O  file  reading
     loop
	      std::putchar(c);

	  if (std::ferror(fp))
	      std::puts("I/O error when reading");
	  else if (std::feof(fp))
	  {
	      std::puts("End of file reached successfully");
	      is_ok = EXIT_SUCCESS;
	  }

	  std::fclose(fp);
	  return is_ok;
      }

Output:
      End of file reached successfully

See also
	fclose	closes a file
		(function)
	fflush	synchronizes an output stream with the actual file
		(function)
	freopen open an existing stream with a different name
		(function)
	C documentation for
	fopen

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