From: "John M. Aldrich" <fighteer AT cs DOT com>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Protected Mode programming
Date: Thu, 29 May 1997 20:43:09 +0000
Organization: Two pounds of chaos and a pinch of salt
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IEX & SAMPLE wrote:
> 
> Hello, I'm new to DJGPP and protected-mode programming, I was
> wondering how do I use protected mode?  Do programs made w/ DJGPP
> automatically go into protected mode when they are run??

Yes.  And you don't need to worry about it at all unless you start
performing hardware-dependent operations, such as graphics and interrupt
handling.  In that case, the techniques you learned for real-mode
compilers will NOT work, and either won't compile or will crash your
programs.

Please get and read the DJGPP Frequently Asked Questions list
(v2/faq210b.zip), which explains a great deal of this stuff and gives
you pointers and examples of things to watch out for in protected mode. 
But just for kicks, try the following program:

/* lotsamem.c */
#include <stdio.h>
#include <stdlib.h>

int main( void )
{
    char *p;
    int megs;

    printf( "How many megabytes would you like to allocate (1-256)? " );
    if ( scanf( "%d", &megs ) < 1 || megs < 1 || megs > 256 )
        printf( "That's not what I asked for, dufus.\n" );
    else
    {
        p = malloc( megs * 1048576 );
        if ( p != NULL )
        {
            printf( "Wow!  You just allocated %d megabytes!\n", megs );
            free( p );
        }
        else
            printf( "Whoops!  You don't have enough memory available. 
Sorry.\n" );
    }
    return 0;
}

Compile it by typing "gcc -o lotsamem.exe lotsamem.c".
Run it by typing "lotsamem".
Enjoy.  ;)

Note:  depending on what DPMI host you run under (cwsdpmi, Windows,
Linux, OS/2, QDPMI, etc.), you may have varying amounts of free memory
and may not be able to allocate it all in one chunk.  But that's an
advanced topic.

-- 
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