From:	csgcty AT singnet DOT com DOT sg
Date:	Fri, 4 Jul 1997 13:55:19 +0800 (SST)
Message-Id:	<199707040555.NAA16962@mallow.singnet.com.sg>
Mime-Version:	1.0
To:	djgpp AT delorie DOT com
Subject:	Re: Memory allocation
Cc:	Nate Eldredge <eldredge AT ap DOT net>, Eli Zaretskii <eliz AT is DOT elta DOT co DOT il>

Thanks for the replies!

>You wrote:
>>I just started using DJGPP and I'm a little confused about memory
>>allocation. There appears to be a few ways to allocate memory : using the
>>new operator, using __dpmi_allocate_dos_memory,
>>__dpmi_allocate_linear_memory, __dpmi_allocate_memory,
>>__dpmi_allocate_shared_memory. Could someone tell me which one I should use
>>and what is the difference between them ? I need to allocate about 1-2 MB. 
>
>Is there some reason you can't just use malloc? This is the most portable
>and simplest way to allocate memory, and all the low-level DPMI stuff is
>done for you.
>
The pointer returned by malloc, what kind of pointer is it ? is it a 32 bit 
offset from somewhere (where ?)? what I need is a offscreen buffer for the 
screen.
What I did was :

int len=2*640*480;
char *p;
int p_ds;

p=malloc(len);
p_ds=__dpmi_allocate_ldt_descriptors(1);
__dpmi_set_segment_base_address(p_ds,(int)p);
__dpmi_set_segment_limit(p_ds,len);

//video_ds defined elsewhere

movedata(video_ds,0,p_ds,0,len);
//do something
movedata(p_ds,0,video_ds,0,len);

The problem was that when len was not too large (< approx 200K)
it was okay, but when it got larger than that, only part of the 
screen was restored other parts were filled with either static or white. 

Please help !

Thanks

Chan Tze Yi

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