_sopen - Open Shared File

Syntax

#include <fcntl.h>
#include <sys\stat.h>
#include <share.h>
#include <io.h>
int _sopen(char *pathname, int oflag, int shflag, int pmode);

Description

• sopen opens the file specified by pathname and prepares the file for subsequent shared reading or writing as defined by oflag and shflag. The oflag is an integer expression formed by combining one or more of the constants defined in <fcntl.h>. When more than one constant is given, the constants are joined with the OR operator (|). compact break=fit.

  Oflag

  Meaning
  O_APPEND
  Reposition the file pointer to the end of the file before every write operation.
  O_CREAT
  Create and open a new file. This flag has no effect if the file specified by pathname exists.
  O_EXCL
  Return an error value if the file specified by pathname exists. This flag applies only when used with O_CREAT.
  O_RDONLY
  Open the file for reading only. If this flag is given, neither O_RDWR nor O_WRONLY can be given.
  O_RDWR
  Open the file for both reading and writing. If this flag is given, neither O_RDONLY nor O_WRONLY can be given.
  O_TRUNC
  Open and truncate an existing file to 0 length. The file must have write permission. The contents of the file are destroyed. On the OS/2 operating system, do not specify O_TRUNC with O_RDONLY.
  O_WRONLY
  Open the file for writing only. If this flag is given, neither O_RDONLY nor O_RDWR can be given.
  O_BINARY
  Open the file in binary (untranslated) mode.
  O_TEXT
  Open the file in text (translated) mode. (See "Stream Processing" in the Programming Guide for a description of text and binary mode.)

  The shflag argument is one of the following constants, defined in <share.h>: compact break=fit.

  Shflag

  Meaning
  SH_DENYRW
  Deny read and write access to file.
  SH_DENYWR
  Deny write access to file.
  SH_DENYRD
  Deny read access to file.
  SH_DENYNO
  Permit read and write access.

  There is no default value for the shflag.

  The pmode argument is required only when you specify O_CREAT. If the file does not exist, pmode specifies the permission settings of the file, which are set when the new file is closed for the first time. If the file exists, the value of pmode is ignored. The pmode must be one of the following values, defined in <sys\stat.h>: compact break=fit.

  Value

  Meaning
  S_IWRITE
  Writing permitted
  S_IREAD
  Reading permitted
  S_IREAD | S_IWRITE
  Reading and writing permitted.

  If write permission is not given, the file is read-only. On the OS/2 operating system, all files are readable; you cannot give write-only permission. Thus, the modes S_IWRITE and S_IREAD | S_IWRITE are equivalent. Specifying a pmode of S_IREAD is similar to making a file read-only with the ATTRIB system command.

  _sopen applies the current file permission mask to pmode before setting the permissions. (See umask for information on file permission masks.)

Returns

• sopen returns a file handle for the opened file. A return value of -1 indicates an error, and errno is set to one of the following values: compact break=fit.

  Value

  Meaning
  EACCESS
  The given path name is a directory, but the file is read-only and at attempt was made to open if for writing, or a sharing violation occurred.
  EEXIST
  The O_CREAT and O_EXCL flags are specified, but the named file already exists.
  EMFILE
  No more file handles are available.
  ENOENT
  The file or path name was not found.
  EINVAL
  An incorrect argument was passed.
  EOS2ERR
  The call to the operating system was not successful.
Example Code

This example opens the file sopen.datforsharedreadingandwritingusing_ sopen .Itthenopensthefileforsharedreading .

#include <io.h>#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <share.h>

#define FILENAME "sopen.dat"

int main(void)
{
   int fh1,fh2;

   printf("Creating file.\n");
   system("echo Sample Program > " FILENAME);

   /* share open the file for reading and writing                            */
   if (-1 == (fh1 = _sopen(FILENAME, O_RDWR, SH_DENYNO))) {
      perror("sopen failed");
      remove(FILENAME);
      return EXIT_FAILURE;
   }
   /* share open the file for reading only                                   */
   if (-1 == (fh2 = _sopen(FILENAME, O_RDONLY, SH_DENYNO))) {
      perror("sopen failed");
      close(fh1);
      remove(FILENAME);
      return EXIT_FAILURE;
   }
   printf("File successfully opened for sharing.\n");
   close(fh1);
   close(fh2);
   remove(FILENAME);
   return 0;

   /****************************************************************************
      The output should be:

      Creating file.
      File successfully opened for sharing.
   ****************************************************************************/
}

Related Information

• close
  
• creat
  
• open
  
• fdopen
  
• fopen
  
• sopen
  
• umask

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