Q60488: Apparent Failure of _memavl() Caused by printf() Allocation

Article: Q60488
Product(s): See article
Version(s): 6.00   | 6.00
Operating System(s): MS-DOS | OS/2
Keyword(s): ENDUSER| | mspl13_c
Last Modified: 15-APR-1990

The printf() statement makes a call to malloc() the first time it is
called within a program. Due to this allocation, _memavl() may seem to
return an incorrect value in some cases.

If a call to _memavl() is made within or before the first printf()
statement in a program, subsequent malloc() calls cannot allocate as
much memory as _memavl() suggests.

The workaround is to make the call to printf() before your call to
_memavl(), or make another call to _memavl() after printf() to
determine your true maximum allocation.

The following code demonstrates the problem:

#include<malloc.h>
#include<stdio.h>

size_t mavl;
char *ptr;

void main(void)
{
// printf("If included, this line solves the problem.\n");

   printf("memory available=%u \n",mavl=_memavl());

   if ((ptr=(char *)malloc(mavl))==NULL)
     printf("Not as much memory available as we thought!");
}

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