Determining That SHARE Is Loaded Under Microsoft Windows

The information in this article applies to:

• Microsoft Windows Software Development Kit (SDK) for Windows versions 3.0 and 3.1

SUMMARY

To determine whether the SHARE.EXE application is loaded, an application typically calls MS-DOS Interrupt 2Fh Function 1000h. However, this method always returns true in enhanced mode Microsoft Windows versions 3.0 and 3.1 even if the SHARE is not loaded.

Windows returns true for Interrupt 2Fh Function 1000h to prevent SHARE from installing itself in an MS-DOS virtual machine (VM) under Windows. If SHARE installed a local copy in a VM, the system would become unstable and data corruption on the hard drive(s) might result.

MORE INFORMATION

To determine under enhanced mode Windows whether SHARE is installed, call Interrupt 21h Function 5Ch to lock a region of a file. This function is available only when SHARE is installed, and unlike using the OpenFile function with sharing modes, the lock region function always fails with error 1 (invalid function) if SHARE is not loaded. Perform the following six steps to determine whether SHARE is loaded:

1. Create a temporary file using MS-DOS Interrupt 21h Function 5Ah.

2. Lock a region of the returned temporary file using MS-DOS Interrupt 21h Function 5Ch. Set AL = CX = DX = SI = 0 and DI = 1.

3. If the call in step 2 returns with the carry flag set and AX = 1, SHARE is not loaded. Move to step 5.

4. SHARE is loaded. Unlock the region of the file using MS-DOS Interrupt 21h Function 5Ch. Set CX = DX = SI = 0 and AL = DI = 1.

5. Close the file using MS-DOS Interrupt 21h Function 3Eh.

6. Delete the file using MS-DOS Interrupt 21h Function 41h.