In what cases should I use memcpy over standard operators in C++?

Question

When can I get better performance using memcpy or how do I benefit from using it? For example:

float a[3]; float b[3];

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Answer 1

You can use memcpy only if the objects you're copying have no explicit constructors, so as their members (so-called POD, "Plain Old Data"). So it is OK to call memcpy for float, but it is wrong for, e.g., std::string.

But part of the work has already been done for you: std::copy from is specialized for built-in types (and possibly for every other POD-type - depends on STL implementation). So writing std::copy(a, a + 3, b) is as fast (after compiler optimization) as memcpy, but is less error-prone.