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_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:

Open for reading only. _fdopen returns NULL if the file cannot be opened. 
Create for writing. If the file already exists, its contents are overwritten. 
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,
                  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 
 
 
 
Copyright(C) 2009 Embarcadero Technologies, Inc. All Rights Reserved.
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