What is the fastest portable way to copy an array in C++

Question

This question has been bothering me for some time. The possibilities I am considering are

1. memcpy
2. std::copy
3. cblas_dcopy

Does a

Answer 1

Just Profile your application. You will likely find that copying is not the slowest part of it.

Answer 2

memcpy is probably the fastest way to copy a contiguous block of memory. This is because it will likely be highly optimized to your particular bit of hardware. It is often implemented as a built-in compiler function.

Having said that, and non POD C++ object is unlikely to be contiguous and therefore copying arrays of C++ objects using memcpy is likely to give you unexpected results. When copying arrays (or collections) of C++ objects, std::copy will use the object's own copy semantics and is therefore suitable for use with non POD C++ objects.

cblas_dcopy looks like a copy for use with a specific library and probably has little use when not using that library.