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The pages on this site contain documentation for very old MS-DOS software, purely for historical purposes. If you're looking for up-to-date documentation, particularly for programming, you should not rely on the information found here, as it will be woefully out of date.

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─────Run-Time Library───────────────────────────────────────────────────────
 
/* LOCK.C illustrates network file sharing functions:
 *      _sopen       _locking
 *
 * Also the global variable:
 *      _osmajor
 *
 * The program requires DOS 3.0 or higher. The DOS SHARE command must
 * be loaded. The locking mechanism will only work if the program is
 * run from a network drive.
 */
 
#include <stdio.h>
#include <conio.h>
#include <io.h>
#include <fcntl.h>
#include <sys\types.h>
#include <sys\stat.h>
#include <sys\locking.h>
#include <share.h>
#include <stdlib.h>         /* For _osmajor and exit */
 
void error( char *msg );
 
void main( int argc, char *argv[] )
{
    int handle, i;
    char buf[1], msg[] = "Are any of these bytes locked?";
 
    /* Check for DOS version >= 3.0 */
    if( _osmajor < 3 )
        error( "Must be DOS 3.0 or higher" );
 
    /* If no argument, write file and lock some bytes in it. */
    if( argc == 1 )
    {
        /* Open file with deny none sharing. */
        handle = _sopen( "tmpfil", _O_BINARY | _O_RDWR | _O_CREAT,
                                  _SH_DENYNO, _S_IREAD | _S_IWRITE );
        if( handle == -1 )
            error( "Can't open file\n" );
 
        _write( handle, msg, sizeof( msg ) - 1 );
 
        /* Lock 10 bytes starting at byte 10. */
        _lseek( handle, 10L, SEEK_SET );
        if( _locking( handle, _LK_LOCK, 10L ) )
            error( "Locking failed\n" );
        printf( "Locked 10 bytes starting at byte 10\n" );
 
        /* Run a copy of ourself with argument to test. */
        system( "LOCK read" );
        _getch();
 
        /* Unlock. */
        _lseek( handle, 10L, SEEK_SET );
        _locking( handle, _LK_UNLCK, 10L );
        printf( "\nUnlocked 10 bytes starting at byte 10\n" );
 
        system( "LOCK read" );
        _getch();
    }
 
    /* Try to read some locked bytes. This branch taken during test. */
    else
    {
        /* Open file with deny none sharing. */
        handle = _sopen( "tmpfil", _O_BINARY | _O_RDWR,
                                  _SH_DENYNO, _S_IREAD | _S_IWRITE );
        if( handle == -1 )
            error( "Can't open file\n" );
 
        for( i = 0; i < sizeof( msg ) - 1; i++ )
        {
            /* Print characters until locked bytes are reached. */
            if( _read( handle, buf, 1 ) == -1 )
                break;
            else
                putchar( *buf );
        }
    }
    _close( handle );
    exit( 0 );
}
 
void error( char *errmsg )
{
    printf( errmsg );
    exit( 1 );
}
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