Question

I have an existing 1D array, is memset the fastest way to zero it?

Answer 1

Fastest … probably yes.
Buggy almost sure!

It mostly depends on the implementation, platform and … what type the array contains.

In C++ when a variable is defined its constructor is called. When an array is defined, all the array’s elements’ constructors are called.

Wiping out the memory can be considered “good” only for the cases when the array type is know to have an initial state that can be represented by all zero and for which the default constructor doesn’t perform any action.

This is in general true for built-in types, but also false for other types.

The safest way is to assign the elements with a default initialized temporary.

template<class T, size_t N>
void reset(T* v)
{
    for(size_t i=0; i<N; ++i) 
        v[i] = T();
}

Note that, if T is char, the function instantiates and translates exactly as memset. So it is the same speed, no more no less.