Header File 

stdio.h, share.h 

Category 

Input/output Routines 

Prototype 

FILE *_fsopen(const char *filename, const char *mode, int shflag); 

FILE *_wfsopen(const wchar_t *filename, const wchar_t *mode, int shflag); 

Description 

Opens a stream with file sharing. 

_fsopen opens the file named by filename and associates a stream with it. _fsopen returns a pointer that is used to identify the stream in subsequent operations. 

The mode string used in calls to _fsopen is one of the following values:

To specify that a given file is being opened or created in text mode append a t to the mode string (rt w+t and so on). Similarly to specify binary mode append a b to the mode string (wb a+b and so on). _fsopen also allows the t or b to be inserted between the letter and the + character in the mode string; for example rt+ is equivalent to r+t. If a t or b is not given in the mode string the mode is governed by the global variable _fmode. If _fmode is set to O_BINARY files are opened in binary mode. If _fmode is set to O_TEXT they are opened in text mode. These 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 _fsopen returns a pointer to the newly opened stream.  

On error it returns NULL. 

Example  

#include <io.h>
#include <process.h>
#include <share.h>
#include <stdio.h>
int main(void)
{
  FILE *f;
  int status;
  f = _fsopen("TESTFILE.DAT", "r", SH_DENYNO);
  if (f == NULL)
  {
    printf("_fsopen failed\n");
    exit(1);
  }
  status = access("TESTFILE.DAT", 6);
  if (status == 0)
    printf("read/write access allowed\n");
  else
    printf("read/write access not allowed\n");
  fclose(f);
  return 0;
}

Portability