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];
    ...
}
cat         


        

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.