The function 48h fails when I want to allocate some memory

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Vortex

Joined: 17 Jun 2003
Posts: 318

Vortex 17 Jun 2003, 11:17

The function 48h fails when I want to allocate some memory:

Code:

format MZ

   push    cs
  pop     ds

        mov     ah,048h
        mov     bx,10   ;Allocate 10*16 bytes
        int     21h
        jnb     @f      ;Allocation successfull
        mov     dx,errmsg
        mov     ah,9
   int     21h
@@:
      mov     ax,4C00h
    int     21h

errmsg  db 'Error',24h

Setting the carry flag whick means failure...
What can be the reason? Are there different methods to allocate
memory under DOS?

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17 Jun 2003, 11:17

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8435
Location: Kraków, Poland

Tomasz Grysztar 17 Jun 2003, 11:22

From the fasm documentation (section 2.4.1):

Quote:

"heap" directive should be followed by a 16-bit value defining maximum size
of additional heap in paragraphs (this is heap in addition to stack and
undefined data). Use "heap 0" to always allocate only memory program really
needs. Default size of heap is 65535.

With default heap size all conventional memory gets allocated when your program is loaded and thus you can't allocate more. Setting heap to zero should help.

17 Jun 2003, 11:22

Vortex

Joined: 17 Jun 2003
Posts: 318

Vortex 17 Jun 2003, 11:43

Thanks Privalov,it works now. Smile

I have an other question,is there an eqivalent instruction to adjust
the heapsize for other assemblers such as tasm and masm?

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17 Jun 2003, 11:43

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8435
Location: Kraków, Poland

Tomasz Grysztar 17 Jun 2003, 12:27

Yes, this is usually one of the switches for the linker.

17 Jun 2003, 12:27

Vortex

Joined: 17 Jun 2003
Posts: 318

Vortex 18 Jun 2003, 10:08

Thanks Privalov.Everything works fine.

_________________
Code it... That's all...

18 Jun 2003, 10:08

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