Q47758: SETMEM(0) Returns Total Heap, FRE(-1) Returns Available Heap

Article: Q47758
Product(s): See article
Version(s): 4.00 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | B_BasicCom | mspl13_basic
Last Modified: 15-DEC-1989

The program shown below demonstrates the difference between the
SETMEM(0) and FRE(-1) functions. SETMEM(0) returns the TOTAL possible
amount of far heap space, while FRE(-1) returns the far heap space
minus any data (in DGROUP or far heap) that is currently allocated.
For Microsoft BASIC PDS Version 7.00, FRE(-1) refers only to far heap;
to get available expanded memory you must use FRE(-3).

This information applies to QuickBASIC Versions 4.00, 4.00b, and 4.50,
to Microsoft BASIC Compiler Versions 6.00 and 6.00b for MS-DOS, and to
Microsoft BASIC PDS Version 7.00 for MS-DOS.

The following program is MEMSIZE.BAS, which invokes SETMEM(0) and
FRE(-1) before and after allocating a data string:

CLS
PRINT "Setmem                        : "; SETMEM(0)
PRINT "Nonstring array             -1: "; FRE(-1)
a$ = SPACE$(200)
PRINT
PRINT "      --- After Allocation ---"
PRINT "Setmem                        : "; SETMEM(0)
PRINT "Nonstring array             -1: "; FRE(-1)

After the string is allocated, SETMEM(0) returns the same value as it
did before the call. FRE(-1), however, is decreased by the size of the
string (200 bytes for the string plus 2 bytes for the string
descriptor).

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