_fdopen, _wfdopen

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

Copy Code

#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,
                  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		+

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