Hello,

I have a problem with malloc and realloc.

When coreleft is under 9500 bytes, malloc return NULL.

my parameters to compile are: -2 -Pz -Jm -R -Ab -msd -o+space -Nc -Ns main.c

Thanks to help me to resolve the problem.

Hello,

I made some new test:
coreleft, stackavail and _chkstack return a value >8000
and _heapchk return -2  (_HEAPOK)

BUT

_memavl() doesn't return anything, and the programm doesn't respond (and I need to
reset everything)

I hope this test will help to resolve my problem

veb wrote:
> I hope this test will help to resolve my problem

This could very well be a pointer bug in your program, which is difficult to resolve in the -ms memory model. What I do is thoroughly debug a program first in 32 bit mode, then try porting it to 16 bits.

Walter Bright wrote:
>This could very well be a pointer bug in your program, which is >difficult to resolve in the -ms memory model. What I do is thoroughly debug a >program first in 32 bit mode, then try porting it to 16 bits.

I made another test:
I affected a different value to unsigned __cdecl _stack
When it is too small, Some operations don't work, but I can allocate more memory
than if _stack is bigger.
Which size is best for _stack ? (or how allocate in _stack ?)
How to calculate exactly how many memory I can still allocate when the programm
runs? (since memavl() doesn't work)

Thanks

veb wrote:
> Walter Bright wrote:
>> This could very well be a pointer bug in your program, which is >difficult to
>> resolve in the -ms memory model. What I do is thoroughly debug a >program first
>> in 32 bit mode, then try porting it to 16 bits.
> 
> I made another test:
> I affected a different value to unsigned __cdecl _stack
> When it is too small, Some operations don't work, but I can allocate more memory
> than if _stack is bigger.
> Which size is best for _stack ? (or how allocate in _stack ?)
> How to calculate exactly how many memory I can still allocate when the programm
> runs? (since memavl() doesn't work)

The default is the best size for _stack.

At the level you're working at, I suggest studying the source code for malloc(), etc. It isn't too complicated, and when you're trying to fit things in 64K it helps a lot to understand the details all the way down.

Walter Bright wrote:
> The default is the best size for _stack.
> At the level you're working at, I suggest studying the source code for malloc(),
> etc. It isn't too complicated, and when you're trying to fit things in 64K it
> helps a lot to understand the details all the way down.

Ok,

I look for malloc's source in the sources of open watcom, and I don't really realize why _stack needs to be big.

I would like to reduce the size of _stack,
 and I would instead alloc many time a small buffer with malloc to alloc a big
buffer (will it work?)

For example if I write unsigned __cdecl _stack=2048;
and would like to allocate a 1024 bytes buffer, should I write:
"buffer=realloc(buffer,500); buffer = realloc(buffer,1024);"
instead of"buffer=realloc (buffer,1024);" ?

Thanks for your help

veb wrote:
> Walter Bright wrote:
>> The default is the best size for _stack.
>> At the level you're working at, I suggest studying the source code for malloc(),
>> etc. It isn't too complicated, and when you're trying to fit things in 64K it
>> helps a lot to understand the details all the way down.
> 
> Ok,
> 
> I look for malloc's source in the sources of open watcom, and I don't really
> realize why _stack needs to be big.

Looking in Watcom's source code won't help much, should look in Digital Mars' sources.


> I would like to reduce the size of _stack,
>  and I would instead alloc many time a small buffer with malloc to alloc a big
> buffer (will it work?)
> 
> For example if I write unsigned __cdecl _stack=2048;
> and would like to allocate a 1024 bytes buffer, should I write:
> "buffer=realloc(buffer,500); buffer = realloc(buffer,1024);"
> instead of"buffer=realloc (buffer,1024);" ?
> 
> Thanks for your help

I'd just use 1024.