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/*
** 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.
**
** Example of usage:
**
** main(int argc, char *argv[])
** {
** int sharing;
**
** sharing = is_share(argv[0]);
** .
** .
** if (sharing)
** {
** // open file in shared mode
** ...
** }
** else
** {
** // use "normal" open
** ...
** }
** }
**
** Revision History:
**
** 08/03/93 Original: "is_sharing()" by Mike Ratledge of fidonet
** 10/20/93 Revision: revised for library
** 04/03/94 Revision: "Portabalized" for SNIPPETS by Bob Stout
*/
#include <stdio.h>
#include <io.h>
#include <dos.h>
#if defined(_MSC_VER)
#include <stdlib.h>
#include <sys\locking.h>
int lock(int fp, long ofs, long lng)
{
lseek(fp,0L,SEEK_SET);
return locking(fp,LK_LOCK,lng);
}
int unlock(fp,ofs,lng)
{
lseek(fp,0L,SEEK_SET);
return locking(fp,LK_UNLCK,lng);
}
#endif
int is_share(char *arg)
{
FILE *exe;
if (_osmajor < 3)
return(0);
exe = fopen(arg, "rb");
if (0 == lock(fileno(exe), 0l, 500l))
{
unlock(fileno(exe), 0l, 500l);
fclose(exe);
return(1);
}
fclose(exe);
return(0);
}
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