How can I open a file so that other programs can update it at the same time? in C programming

How can I open a file so that other programs can update it at the same time?

 Your C compiler library contains a low-level file function called sopen() that can be used to open a file in
shared mode. Beginning with DOS 3.0, files could be opened in shared mode by loading a special program
named SHARE.EXE. Shared mode, as the name implies, allows a file to be shared with other programs as
well as your own. Using this function, you can allow other programs that are running to update the same
file you are updating.
The sopen() function takes four parameters: a pointer to the filename you want to open, the operational
mode you want to open the file in, the file sharing mode to use, and, if you are creating a file, the mode to
create the file in. The second parameter of the sopen() function, usually referred to as the “operation flag”
parameter, can have the following values assigned to it

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Constant                                                   Description

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O_APPEND                                            Appends all writes to the end of the file
O_BINARY                                             Opens the file in binary (untranslated) mode
O_CREAT                                               If the file does not exist, it is created
O_EXCL                                                 If the O_CREAT flag is used and the file exists, returns an error
O_RDONLY                                           Opens the file in read-only mode
O_RDWR                                               Opens the file for reading and writing
 O_TEXT                                                Opens the file in text (translated) mode
O_TRUNC                                             Opens an existing file and writes over its contents
O_WRONLY                                          Opens the file in write-only mode
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The third parameter of the sopen() function, usually referred to as the “sharing flag,” can have the following
values assigned to it:
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Constant                                                  Description
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SH_COMPAT                                         No other program can access the file
SH_DENYRW                                       No other program can read from or write to the file
SH_DENYWR                                       No other program can write to the file
SH_DENYRD                                        No other program can read from the file
SH_DENYNO                                       Any program can read from or write to the file
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If the sopen() function is successful, it returns a non-negative number that is the file’s handle. If an error occurs, –1 is returned, and the global variable errno is set to one of the following values:
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Constant                                                  Description
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ENOENT                                               File or path not found
EMFILE                                                 No more file handles are available
EACCES                                                Permission denied to access file
EINVACC                                              Invalid access code
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The following example shows how to open a file in shared mode
:
#include <stdio.h>
#include <fcntl.h>
#include <sys\stat.h>
#include <io.h>
#include <share.h>
void main(void);
void main(void)
{
int file_handle;
/* Note that sopen() is not ANSI compliant */
file_handle = sopen(“C:\\DATA\\TEST.DAT”, O_RDWR, SH_DENYNO);
close(file_handle);
}
Whenever you are sharing a file’s contents with other programs, you should be sure to use the standard C
library function named locking() to lock a portion of your file when you are updating it. See FAQ IV.15
for an explanation of the locking() function

Cross Reference:
IV.14: How can I make sure that my program is the only one accessing a file?
IV.15: How can I prevent another program from modifying part of a file that I am modifying?