Virtual allocated array template

virtual_array.cpp

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

#define WIN32_LEAN_AND_MEAN
#define VC_EXTRALEAN
#include <windows.h>

template <class T> struct Virtual_Array {
    
    T *data = nullptr;
    unsigned int count = 0;
    unsigned int allocated = 0; // Only stores 4 billion items, but that could easily be increased.
    
    void reserve_bytes() {
        data = (T *)VirtualAlloc(nullptr, sizeof(T) * 0x100000000, MEM_RESERVE, PAGE_NOACCESS);
        //printf("Reserving %llu pages\n", sizeof(T) * 0x100000000 / 4096);
    }
    
    void commit_as_needed(unsigned int new_count) {
        if (!data) {
            reserve_bytes();
        }
        if (allocated <= new_count) {
            if (allocated < 1) allocated = 1;
            do {
                allocated *= 2;
            } while (allocated <= new_count);
            
            //printf("Committing %u items\n", allocated);
            
            VirtualAlloc(data, allocated * sizeof(T), MEM_COMMIT, PAGE_READWRITE);
        }
    }
    
    void release() {
        VirtualFree(data, 0, MEM_RELEASE);
        data = nullptr;
        count = 0;
        allocated = 0;
    }
    
    T &operator[](signed long long i) {
        assert(i >= 0);
        assert(i < count);
        return data[(unsigned int)i];
    }
    
    T *push(T value) {
        assert(count < 0xffffffff);
        
        commit_as_needed(count + 1);
        
        T *result = &data[count];
        count += 1;
        *result = value;
        return result;
    }
    
    T *begin() { return data; }
    T *end() { return data + count; }
};

int main() { // WARNING, this test takes 8 gigs of ram, and a couple seconds to run.
    
    Virtual_Array<Virtual_Array<int>> arrays;
    for (int i = 0; i < 2; i += 1) {
        Virtual_Array<int> dummy = {};
        arrays.push(dummy);
    }
    for (auto &&a : arrays) {
        for (int i = 0; i < 1024 * 1024 * 1024; i += 1) {
            a.push({i});
        }
        //a.push({1024});
        
        printf("%d\n", a[rand() % a.count]);
    }
    for (auto &&a : arrays) a.release();
    arrays.release();
    return 0;
}