How Do You Initialize constexpr References in C ?

Understanding constexpr References and Their Initialization

Unlike const references, constexpr references offer the guarantee that they are initialized before the program's execution commences. However, their definition and initialization can be subject to specific constraints, as exemplified in the provided code.

To effectively define and initialize constexpr references, consider the following:

1. Binding to Global Variables:
Unlike references to const that can bind to local variables initialised during runtime, constexpr references must bind to global variables or objects with static storage duration. This is because a constexpr reference is analogous to taking the address of a variable, and the address of a local variable is not constant.

2. Example with Static Storage Duration:

<code class="cpp">#include <iostream>

constexpr int x{20}; // Global variable with static storage duration

constexpr int& f() // Function returning a constexpr reference to a global variable
{
    return x;
}

int main()
{
    constexpr int& z = f(); // Initialize constexpr reference with a global constexpr function
    std::cout << z << std::endl; // Access the referenced value
}</code>

In this example, we define a global variable x with static storage duration and a constexpr function f() that returns a constexpr reference to it. Inside main, we create a constexpr reference z initialized with the value returned by f(). This initialization is valid because the value of x is known at compile time.

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