[c++] Constexpr member functions
In C++, a constexpr member function is a member function of a class that can be evaluated at compile time. Using constexpr member functions allows the computation of values to occur at compile time, which can improve performance and efficiency.
Overview
- C++11 introduced the
constexprkeyword to indicate that a function or object can be evaluated at compile time. - C++14 extended the capabilities of
constexpr, allowing the use ofconstexprmember functions.
Syntax
Here’s the syntax for defining a constexpr member function in a C++ class:
class MyClass {
public:
constexpr int compute() const {
// code to compute and return a value
}
};
In this example, the compute member function is declared as constexpr, allowing it to be evaluated at compile time.
Benefits
Using constexpr member functions offers several benefits:
- Performance: Compile-time evaluation can eliminate runtime overhead.
- Efficiency: Avoids redundant computation during program execution.
- Constant expressions:
constexprmember functions can be used in constant expressions, providing more flexibility and optimization opportunities for the compiler.
Example
class Circle {
public:
constexpr Circle(double radius) : radius(radius) {}
constexpr double area() const {
return 3.14159 * radius * radius;
}
private:
double radius;
};
int main() {
constexpr Circle c(5.0);
constexpr double circleArea = c.area();
// 'circleArea' is computed at compile time
return 0;
}
In this example, the area member function of the Circle class is declared as constexpr, allowing the computation of the circle’s area to occur at compile time.