Avoid Function Pointers

Avoid Function Pointers

C++ allows a data type called a “function pointer” or a “pointer to a function” as part of its standard language. These are carefully type controlled, so they are reasonably efficient. However, they are not any faster than regular function calls, just because they're a fancy pointer construct, and there's a simple reason that they're not super-efficient: they're function calls!

A function pointer is a call to a function, so it has the whole sequence to implement. It's not much worse than a standard function call, but there's another problem. Function pointers make it difficult for the C++ compiler to get rid of the function call. The use of a function pointer will obscure much of the normal compile-time optimization logic. Hence, function pointers can be less efficient for:

• inline functions
• constexpr functions
• Intrinsic functions

In summary, they're a neat feature of C++, but not an efficiency gain. Use function pointers if they are convenient, but not as a speedup.

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