Question

I know that Windows 32-bit allows for any process about 2 Gigabyte memory address space as a maximum. 2 Gigabytes = 2147483648 bytes. I tried to allocate heap memory much more than 2147483648 bytes and I saw no error or exception, this the code:

# include<iostream>

int main(){

    void *x=malloc(2147489999);
    free(x);
    system("pause");
    return 0;
}

what is the reason?

Answer 1

You’re not checking the return value 🙂

#include <windows.h>
#include <malloc.h>
#include <stdio.h>
#include<iostream>

#define PAUSE getchar

int 
main(int argc, char *argv[])
{
    void *x=malloc(2147489999);
    if (x)
    {
      printf ("malloc succeeded: 0x%x...\n", x);
      free(x);
    }
    else
    {
      perror ("malloc failed");
    }
    PAUSE ();
    return 0;
}

C:\temp>\bin\vcvars32 Setting environment for using Microsoft Visual
C++ tools. C:\temp>notepad tmp.cpp

C:\temp>cl tmp.cpp Microsoft (R) 32-bit C/C++ Optimizing Compiler
Version 12.00.8168 for 80×86 Copyright (C) Microsoft Corp 1984-1998.
All rights reserved.

tmp.cpp … /out:tmp.exe tmp.obj

C:\temp>tmp malloc failed: No error