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/* LOCKING.C: This program opens a file with sharing. It locks
* some bytes before reading them, then unlocks them. Note that the
* program works correctly only if the following conditions are met:
* - The file exists
* - The program is run with MS-DOS version 3.0 or later
* with file sharing installed (SHARE.COM or SHARE.EXE), or
* if a Microsoft Networks compatible network is running
*/
#include <crt\io.h>
#include <sys\types.h>
#include <sys\stat.h>
#include <sys\locking.h>
#include <share.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#define STRING "0123456789012345678901234567890123456789012345678"
void
_cdecl
main( void )
{
int fh, numread;
char buffer[60];
/* Quit if can't open file or MS-DOS version doesn't support sharing. */
fh = _sopen( "test.txt",
_O_CREAT | _O_TRUNC | _O_RDWR,
_SH_DENYNO,
_S_IREAD | _S_IWRITE );
if( (fh == -1) || (_osmajor < 3) ) {
printf( "Cannot create/open file\n" );
exit( 1 );
}
_write( fh, STRING, sizeof(STRING));
_write( fh, STRING, sizeof(STRING));
_write( fh, STRING, sizeof(STRING));
_write( fh, STRING, sizeof(STRING));
_write( fh, STRING, sizeof(STRING));
_write( fh, STRING, sizeof(STRING));
/* Lock some bytes and read them. Then unlock. */
lseek( fh, 0L, SEEK_SET );
if( _locking( fh, LK_NBLCK, 50L ) != -1 )
{
printf( "No one can change these bytes while I'm reading them\n" );
numread = _read( fh, buffer, 50 );
printf( "%d bytes read: %.50s\n", numread, buffer );
lseek( fh, 0L, SEEK_SET );
_locking( fh, LK_UNLCK, 50L );
printf( "Now I'm done. Do what you will with them\n" );
}
else
perror( "Locking failed\n" );
lseek( fh, 4096L, SEEK_SET );
if( _locking( fh, LK_NBLCK, 1024L ) != -1 )
{
printf( "The lock off the end of the file worked ok\n" );
//lseek( fh, 4096L, SEEK_SET );
if( _locking( fh, LK_UNLCK, 1024L ) == -1 )
printf( "The second unlock failed\n" );
}
else
perror( "Locking failed\n" );
_close( fh );
}
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