_fdopen, _wfdopen

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Header File

stdio.h

Category

Input/output Routines

Prototype

FILE *_fdopen(int handle, char *type);

FILE *_wfdopen(int handle, wchar_t *type);

Description

Associates a stream with a file handle.

_fdopen associates a stream with a file handle obtained from creat, dup, dup2, or open.

The type of stream must match the mode of the open handle.

The type string used in a call to _fdopen is one of the following values:

r	Open for reading only. _fdopen returns NULL if the file cannot be opened.
w	Create for writing. If the file already exists, its contents are overwritten.
a	Append; open for writing at end-of-file or create for writing if the file does not exist.
r+	Open an existing file for update (reading and writing). _fdopen returns NULL if the file cannot be opened.
w+	Create a new file for update. If the file already exists, its contents are overwritten.
a+	Open for append; open (or create if the file does not exist) for update at the end of the file.

To specify that a given file is being opened or created in text mode, append t to the value of the type string (for example, rt or w+t).

Similarly, to specify binary mode, append b to the type string (for example, rb or w+b).

If t or b is not given in the type string, the mode is governed by the global variable _fmode.

If _fmode is set to O_BINARY, files will be opened in binary mode.

If _fmode is set to O_TEXT, files will be opened in text mode.

Note: The O_... constants are defined in fcntl.h.

When a file is opened for update, both input and output can be done on the resulting stream; however,

• output cannot be directly followed by input without an intervening fseek or rewind
• input cannot be directly followed by output without an intervening fseek, rewind, or an input that encounters end-of-file

Return Value

On successful completion _fdopen returns a pointer to the newly opened stream. In the event of error it returns NULL.

Example

#include <sys\stat.h>
#include <stdio.h>
#include <fcntl.h>
#include <io.h>
int main(void)
{
   int handle;
   FILE *stream;
   /* open a file */
   handle = open("DUMMY.FIL", O_CREAT | O_WRONLY,
                  S_IREAD | S_IWRITE);
   /* now turn the handle into a stream */
   stream = fdopen(handle, "w");
   if (stream == NULL)
      printf("fdopen failed\n");
   else
   {
      fprintf(stream, "Hello world\n");
      fclose(stream);
   }
   return 0;
}

Portability

	POSIX	Win32	ANSI C	ANSI C++
_fdopen	+	+
_wfdopen		+