isshare.c

c语言库函数！里面包含了所以c语言中的系统函数的实现及其详细说明和代码！请大家及时下载！

/* +++Date last modified: 05-Jul-1997 */

/*
** is_share() - This is a routine that allows a program to determine
**              if file-sharing is enabled at run-time.
**
**              What does this code do?  First - it checks to make sure
**              it is running under DOS 3.0+ - otherwise - no sharing.
**              Next, it opens the program itself (the .EXE file) by using
**              "argv[0]".  This argument points to the actual program name
**              complete with the path under DOS 3.0 or later.  It then
**              attempts to lock the first 500 bytes of the program on
**              disk.  If successful (i.e. return != -1), it unlocks the
**              locked bytes and closes the file (actually the unlock is
**              superfluous since closing the file releases all locks) and
**              returns the a "TRUE" (1) result.  If it fails, it closes
**              the .EXE file and returns a "FALSE" (0) result.  Note that
**              this does not depend on opening a file in shared mode to
**              test it.
**
** Revision History:
**
** 08/03/93  Original:  "is_sharing()" by Mike Ratledge of fidonet
** 10/20/93  Revision:  revised for library
** 04/03/94  Revision:  "Portabilized" for SNIPPETS by Bob Stout
*/

#include <stdio.h>
#include <io.h>
#include <dos.h>
#include "snpdosys.h"
#include "errors.h"

#if !defined(__TURBOC__)
 #include <stdlib.h>
 #include <sys\locking.h>

 int lock(int fp, long ofs, long lng)
 {
       lseek(fp,ofs,SEEK_SET);
       return locking(fp,LK_LOCK,lng);
 }

 int unlock(int fp, long ofs, long lng)
 {
       lseek(fp,ofs,SEEK_SET);
       return locking(fp,LK_UNLCK,lng);
 }
#endif

int is_share(char *arg)
{
      FILE *exe;

      if (_osmajor < 3)
            return(0);

      exe = cant(arg, "rb");

      if (0 == lock(fileno(exe), 0L, 500L))
      {
            unlock(fileno(exe), 0L, 500L);
            fclose(exe);
            return(1);
      }

      fclose(exe);
      return(0);
}

#ifdef TEST

#ifdef __WATCOMC__
 #pragma off (unreferenced);
#endif

#ifdef __TURBOC__
 #pragma argsused
#endif

main(int argc, char *argv[])
{
      int sharing = is_share(argv[0]);

      printf("File sharing is%s enabled\n", sharing ? "" : " not");
      return 0;
}

#endif /* TEST */