Why am I getting "Invalid Allocation Size: 4294967295 Bytes" instead of an std::bad_alloc exception?

Question

I wrote the following piece of code to allocate memory for an array:

try {
    int n = 0;
    cin >> n;
    double *temp = new double[n];
    ...
}
catch(exception& e) {
    cout << "Standard exception: " << e.what() << endl;
    exit(1);
}

Of course I'm checking n for negative values etc. but when I enter some large Number over 536*(10^6) I'm not getting a bad-alloc exception but a "Invalid Allocation Size: 4294967295 Bytes" Crash.

E.G. I enter n = 536*(10^6) --> bad-alloc exception I enter n = 537*(10^6) --> Invalid Allocation Size: 4294967295 Bytes --> Crash

Any ideas why this is happening?

Answer 1

Calling new double[n] calls the global operator new function with a size of n * sizeof(double). If operator new then finds it cannot fulfil the request, it throws an exception.

However, that cannot happen here: the product of n and sizeof(double) is so large that it is actually not possible to call operator new at all, because the size you requested just plain doesn't fit in a size_t. Implementations vary in how they handle this, but yours evidently aborts the program.

If you want to handle this, you can check that n <= SIZE_MAX / sizeof(double) before attempting your allocation.