Can Static Arrays Be Programmatically Initialized at Compile Time in C ?

Creating Static Arrays Programmatically at Compile Time

In C , static arrays can be initialized at compile time to hold specific values. Consider the following example:

const std::size_t size = 5;    
unsigned int list[size] = { 1, 2, 3, 4, 5 };

Question 1: Assigning Values Programmatically

Is it possible to programmatically assign these values using metaprogramming techniques at compile time?

Answer:

Using C 0x features, it is possible to create local or member arrays of templates and initialize them from a variadic template argument list. However, this is limited by the maximum template instantiation depth and may not be practical for large arrays.

Question 2: Selective Assignment

Assuming certain array elements should have the same value while others vary, can selective assignment be performed programmatically at compile time?

Answer:

Using a template metafunction, one can create an array of values and use it to partially initialize a static array. The following example selectively assigns values based on the index:

template<size_t index> struct MetaFunc { 
    enum { value = index + 1 }; 
};

void test() {
    const std::size_t size = 7;
    typedef generate_array<size, MetaFunc>::result A;

    for (std::size_t i=0; i<size; ++i) { 
        if (i <= 1 || i >= 4) {
            A::data[i] = 0;
        }
    }
}

By leveraging template metafunctions, selective assignment can be achieved in a programmatic manner while ensuring compile-time evaluation.

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