_fsopen, _wfsopen

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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:

r	Open for reading only.	w	Create for writing. If a file by that name already exists, it will be 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).	w+	Create a new file for update (reading and writing). If a file by that name already exists, it will be 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 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

shflag specifies the type of file-sharing allowed on the file filename. Symbolic constants for shflag are defined in share.h.

SH_COMPAT	Sets compatibility mode
SH_DENYRW	Denies read/write access
SH_DENYWR	Denies write access
SH_DENYRD	Denies read access
SH_DENYNONE	Permits read/write access
SH_DENYNO	Permits read/write access

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

	POSIX	Win32	ANSI C	ANSI C++
_fsopen		+
_wfsopen		NT only