constexpr in C++ function declarations: giving constant expressions the power

The constexpr keyword in C allows the declaration of constant expression functions that are evaluated at compile time and produce a constant result. This provides the benefits of compile-time evaluation, optimization opportunities, and protection against accidental modifications. The syntax is: constexpr <return_type> function_name (parameter list). Practical case: constexpr int factorial(int n) { if (n == 0) { return 1; } else { return n * factorial(n - 1); } }

C constexpr in function declarations: giving the power of constant expressions

In C, the constexpr keyword allows you to declare constant expression functions that are evaluated at compile time and produces constant results. This provides the following benefits:

• Compile-time evaluation: Constant expression functions are evaluated at compile time, eliminating the overhead of runtime calculations.
• Optimization opportunities: The compiler can optimize constant expression functions because it knows they will be executed at compile time.
• Prevent accidental modification: The value of a constant expression function cannot be modified at runtime, ensuring data integrity.

Syntax

constexpr The syntax of function declaration is as follows:

constexpr <return_type> function_name(参数列表);

Among them:

• <return_type> is the constant value type returned by the function.
• function_name is the function name.
• Parameter list is the constant expression parameter accepted by the function.

Practical case

The following is a code example using the constexpr constant expression function:

constexpr int factorial(int n) {
  if (n == 0) {
    return 1;
  } else {
    return n * factorial(n - 1);
  }
}

int main() {
  constexpr int result = factorial(5);  // 在编译时求值 factorial(5) 并存储在 result 中
  std::cout << "5 的阶乘为：" << result << std::endl;
  return 0;
}

In this example, ## The #factorial function is a constant expression function that computes the factorial of a number using a recursive algorithm. main The constrent static declaration in the function allows the result of factorial(5) to be calculated at compile time and stored in a result constant middle.

Note

The parameters and return value of the constant expression function must be constant expressions.
• Constant expression functions cannot call non-
• const functions.
Constant expression functions can call other constant expression functions.

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