Hitting memory limits for malloc() at about 1.7GB?

[Skywalker]

I have Vista 64 Ultimate and installed the latest Qt SDK, 2009.03. I seem to be hitting memory limits when using malloc() even though I have 8GB of physical RAM, and task manager shows only 2GB of it is used. My program crashes when I try to allocate large amounts of memory.

The exact limit seems to vary, but it seems to be about 1.74GB. The following code causes my program to crash:

#include <iostream>
#include <qglobal.h>
 
using namespace std;
 
int main(int argc, char *argv[]){
	double* test = (double*) malloc(1863000000);
	cout<<"Test"<<endl;
	test[0] = 1.0;
}

#include <iostream>
#include <qglobal.h>

using namespace std;

int main(int argc, char *argv[]){
	double* test = (double*) malloc(1863000000);
	cout<<"Test"<<endl;
	test[0] = 1.0;
}

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With a slightly smaller number the program executes properly. I don't think Vista Ultimate has a memory limit for processes. Is the latest Qt compiler 64-bit?

How can I utilize my RAM to its fullest extent using malloc() and Qt?