Is there something special you have to do to get large chunks of memory on Windows or in Visual Studio?

Question

This is the call I am making.

table  = (int *) malloc(sizeof(int) * (C+1) * (N+1));

C+1*N+1 comes out to be 657,562,500

But this call is returning a NULL for me when executed on Windows (indicating it could not allocate that amount of space).
(it works fine with a smaller number and also works fine with larger numbers than this on my Linux box)

The program doesn't really do much before this.

When I look at Task Manager it shows 28.1 GB of available memory.

So I am wondering, is there something I can set in Visual Studio like a compiler flag or something that will allow me to grab large chunks of memory like this?

If my math is correct I believe I am asking for about 1.22GB.

Appreciate any help

Edit: So apparently I need to run this as a 64-bit application. Anyone know how to change a c project to 64-bits in visual studio? In configuration parameters under platform Win32 is the only option.

Answer 1

You likely have your project settings set to build a 32-bit Application.

While your computer may have tons of free memory, a 32-bit application cannot use more than 2GB. By my estimate, 4 bytes x 650M is around 2.6 GB.

Try changing your project settings to build for a 64-bit platform.

But still ask yourself why you're allocating so much memory at once. That could well indicate a program design problem.

Answer 2

Too long and involved to make it a comment, so here's how you build it as 64-bit on Visual Studio. I'm on a laptop with VS 2010 rather than 2012, so I may have some details wrong, but this will get you there on 2010 or 2012.

From the IDE, do:

Build / Configuration Manager / Active Solution Platform / New... 

Choose the options shown below. Now you'll be able to build as 64-bit.