Q63003: BASIC 7.00 SETMEM Example Uses malloc/free; Should Be halloc

Article: Q63003
Product(s): See article
Version(s): 7.00 7.10
Operating System(s): MS-DOS
Keyword(s): ENDUSER | SR# S900607-93 docerr | mspl13_basic
Last Modified: 8-JAN-1991

The example for the SETMEM() function on Page 333 of the "Microsoft
BASIC 7.0: Language Reference" manual (for 7.00 and 7.10) incorrectly
uses the C malloc() and free() functions to allocate and free memory
instead of the correct halloc() and hfree() functions.

This information applies to Microsoft BASIC Professional Development
System (PDS) versions 7.00 and 7.10 for MS-DOS.

To be able to free memory for BASIC to reallocate, it is necessary to
use the heap functions [halloc() and hfree()] instead of normal memory
allocation functions. If SETMEM() is used to reallocate memory for
BASIC after using free(), no memory will be reallocated. With hfree(),
the memory will be returned for use with BASIC.

For more information on using SETMEM() with C functions, query on the
following keywords:

   SETMEM and halloc

Code Example
------------

The corrected C code for the SETMEM() example is as follows:

void far cfunc(bytes)
int bytes;
{
    char *halloc();
    char *workspace;

    /* Allocate working memory (halloc) using amount BASIC freed. */
    workspace=halloc((unsigned) bytes, 1);

    /* Working space would be used here. */

    /* Free memory (hfree) before returning to BASIC */
    hfree(workspace);
}

Note: The C code must be compiled using the huge model (/AH).

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