[FIXED] How to get available memory C++/g++?

Issue

I want to allocate my buffers according to memory available. Such that, when I do processing and memory usage goes up, but still remains in available memory limits. Is there a way to get available memory (I don't know will virtual or physical memory status will make any difference ?). Method has to be platform Independent as its going to be used on Windows, OS X, Linux and AIX. (And if possible then I would also like to allocate some of available memory for my application, someone it doesn't change during the execution).

Edit: I did it with configurable memory allocation. I understand it is not good idea, as most OS manage memory for us, but my application was an ETL framework (intended to be used on server, but was also being used on desktop as a plugin for Adobe indesign). So, I was running in to issue of because instead of using swap, windows would return bad alloc and other applications start to fail. And as I was taught to avoid crashes and so, was just trying to degrade gracefully.

Solution

Having read through these answers I'm astonished that so many take the stance that OP's computer memory belongs to others. It's his computer and his memory to do with as he sees fit, even if it breaks other systems taking a claim it. It's an interesting question. On a more primitive system I had memavail() which would tell me this. Why shouldn't the OP take as much memory as he wants without upsetting other systems?

Here's a solution that allocates less than half the memory available, just to be kind. Output was:

Required FFFFFFFF

Required 7FFFFFFF

Required 3FFFFFFF

Memory size allocated = 1FFFFFFF

#include <stdio.h>
#include <stdlib.h>

#define MINREQ      0xFFF   // arbitrary minimum

int main(void)
{
    unsigned int required = (unsigned int)-1; // adapt to native uint
    char *mem = NULL; 
    while (mem == NULL) {
        printf ("Required %X\n", required);
        mem = malloc (required);
        if ((required >>= 1) < MINREQ) {
            if (mem) free (mem);
            printf ("Cannot allocate enough memory\n");
            return (1);
        }
    }

    free (mem);
    mem = malloc (required);
    if (mem == NULL) {
        printf ("Cannot enough allocate memory\n");
        return (1);
    }
    printf ("Memory size allocated = %X\n", required);
    free (mem);
    return 0;
}

Answered By - Weather Vane

Answer Checked By - Willingham (PHPFixing Volunteer)