What are the differences between constexpr and macros in C++20?

What are the differences between constexpr and macros in C++20?

In C++20, constexpr allows for compile-time evaluation of functions and variables, while macros are preprocessor directives that perform text substitution. This means constexpr can provide type safety and better debugging, whereas macros can lead to harder-to-read code.

Can you give an example of how to use constexpr?

Sure! Here's a simple example:

constexpr int square(int x) {
    return x * x;
}

int main() {
    constexpr int result = square(5);
    // result is 25 at compile time
}

What about macros? How do they differ in usage?

Macros are defined using #define. For example:

#define SQUARE(x) ((x) * (x))

int main() {
    int result = SQUARE(5);
    // result is 25, but can lead to issues with expressions
}

Macros don't have type safety and can cause unexpected behavior.

Are there any performance differences between using constexpr and macros?

Yes, constexpr can lead to better performance since it allows for optimizations at compile time, while macros are expanded at preprocessing, which can lead to code bloat and potential runtime inefficiencies.