8. Descriptor Management Services, Continued

8.2 Free Descriptor

This function is used to free descriptors that were allocated through the Allocate Descriptors function.

To Call

     AX = 0001h
     BX = Selector to free

Returns

     If function was successful:
     Carry flag is clear.

     If function was not successful:
     Carry flag is set.

Programmer's Notes

• Since this function involves descriptor management, it will be rarely needed in 32-bit programs.

• Arrays of descriptors are freed by calling this function for each of the individual descriptors.

• It is valid to free the descriptors allocated for the program's initial CS, DS, and SS. Other descriptors that were not allocated by function 0000h should never be freed by this function unless otherwise specified.

Code Sample:

The following function compiles with Watcom C/C++ version 11.0 or later, and Microsoft Visual C/C++ version 4.0 or later:

// de-allocate one descriptor

int dpmiFreeDescriptor(unsigned short sel)	// selector to release
	{
	int result;			// zero if int 31h succeeds
	unsigned short errorCode;	// error code from DPMI host

	__asm {
		mov	bx, sel		// the selector to free

		mov	eax, 0x001	// call dpmi host to do freeing
		int	0x31

		mov	errorCode, ax	// save error code from DPMI, if any

		sbb	eax, eax	// record success/failure flag
		mov	result, eax
		}

	// if the dpmi call failed, return the dpmi error code
	if (result != 0)
		return errorCode;

	// otherwise, indicate success
	return 0;
	}