For additional references for this C++ template info, see below. The compile-time aspect of a constexpr C++ function makes it kind-of C-macro-like, in that if compile-time evaluation is possible for a constexpr function, it will be done at compile-time, same as a MIN() or MAX() macro substitution could possibly be fully evaluated at compile-time in C or C++ too. The constexpr part of the function modifies the function itself and indicates that the function must be capable of being evaluated at compile-time (at least if provided constexpr input parameters), but if it cannot be evaluated at compile-time, then it defaults back to a run-time evaluation, like any other normal function. This is like passing by pointers, and is more efficient for large types, such as class objects. This means the input parameters and return value are passed by reference instead of passed by value. Here you can see that both of the input types, as well as the return type, are const T&, which means "constant reference to type T". Note that the keyword typename is an alias to class (so their usage is identical whether you say or ), since it was later acknowledged after the invention of C++ templates, that the template type might be a regular type ( int, float, etc.) instead of only a class type. The default prototypes for std::max() and std::min(), for instance, in C++14, looking at their prototypes in the links just above, are: template Ĭonstexpr const T& max(const T& a, const T& b) Ĭonstexpr const T& min(const T& a, const T& b) In the C++ standard library they are defined slightly differently than I have them above.
#MAX MACRO IN C HOW TO#
This technique is commonly used, well-respected by those who know how to use it properly, the "de facto" way of doing things, and fine to use if used properly, but buggy (think: double-evaluation side effect) if you ever pass expressions including variable assignment in to compare: #define MAX(a,b) ((a) > (b) ? (a) : (b)) I've done my best to be thorough and factual and correct to make this answer a canonical reference I can come back to again and again, and I hope you find it as useful as I do. 2020: I've also added a Section 3 to show how this would be done with C++ templates too, as a valuable comparison for those learning both C and C++, or transitioning from one to the other. Titarenco nailed it here, but let me at least clean it up a bit to make it look nice, and show both min() and max() together to make copying and pasting from here easier.
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