exception handling ( memory allocation)

Code:

---

#include <iostream>
#include <new>

using std::cout;
using std::endl;
using std::bad_alloc;

int main()
{
        char* pdata = 0;
        size_t count = ~static_cast<size_t>(0) / 3; // if you divide it by two it'll work
        cout << endl
                << count
                << endl << count / 3 << endl;
        try
        {
                pdata = new char[count];
                cout << "Memory allocated." << endl;
        }
        catch(bad_alloc &ex)
        {
                cout << "Memory allocation failed." << endl
                        << "The information from the exception object is: "
                        << ex.what() << endl;
        }

        delete[] pdata;
        return 0;
}

---

Look at the bold part of my code,

When I divide it by 3, the program doesn't responds, but when divide it by 2 the program works and throws an exception but not in the case of 3.

Why?

If you really want to figure out how much memory you can allocate, I would suggest some method like this:

Code:

---

#include <iostream>
#include <new>

using std::cout;
using std::endl;
using std::bad_alloc;


size_t absdiff(size_t a, size_t b)
{
   
    if (a > b)
        return a-b;
    return b-a;
}

int main()
{
    char *pdata;

    size_t max = ~0;
    size_t min = 1024;
    size_t size;
    while(absdiff(min,max) > 1)
    {
        size = (min + max) / 2;
        try
        {
            cout << "trying size " << size << " min=" << min << " Max="
                << max << endl;
            pdata = new char[size];
            cout << "Memory allocated." << endl;
            min = size;
            delete pdata;
        }
        catch(bad_alloc &ex)
        {
            cout << "Memory allocation failed." << endl
                << "The information from the exception object is: "
                << ex.what() << endl;
            max = size;
        }
    }
    cout << "Max size allocation = " << size << endl;
    return 0;
}

---

--
Mats

Well what I wanna know is that why the code provided by me doesn't works,

It throws an exception when you divide it by 2
but the programs stops when you try to divide count by 3


since the number divided by 2 is larger than if that number is divided by 3

so if it can throw an excption to a larger number then why a not smaller number ?


I want to know whats causing that program not to respond.

O_o

When you see local 318 attempting to control a burning house do you blame the firemen for the fire?

Soma

Works for me in either case (doesn't throw).

Perhaps your memory is rather fragmented and the OS has to do a lot of work to provide a contiguous block, so it just appears to be not responding?

Quote:

---

Originally Posted by manzoor

Well what I wanna know is that why the code provided by me doesn't works,

It throws an exception when you divide it by 2
but the programs stops when you try to divide count by 3


since the number divided by 2 is larger than if that number is divided by 3

so if it can throw an excption to a larger number then why a not smaller number ?


I want to know whats causing that program not to respond.

---

I have no idea. Running the code you posted unmodified and compiled with gcc, it works fine.

--
Mats