Possible to initialize an array after the declaration in C?

Question

Is there a way to declare a variable like this before actually initializing it?

    CGFloat components[8] = {
        0.0, 0.0, 0.0, 0.0,
        0.0, 0.0, 0.0, 0.15
    };

I'd like it declared something like this (except this doesn't work):

    CGFloat components[8];
    components[8] = {
        0.0, 0.0, 0.0, 0.0,
        0.0, 0.0, 0.0, 0.15
    };

Answer 1

You cannot assign to arrays so basically you cannot do what you propose but in C99 you can do this:

CGFloat *components;
components = (CGFloat [8]) {
    0.0, 0.0, 0.0, 0.0,
    0.0, 0.0, 0.0, 0.15
};

the ( ){ } operator is called the compound literal operator. It is a C99 feature.

Note that in this example components is declared as a pointer and not as an array.

Answer 2

If you wrap up your array in a struct, it becomes assignable.

typedef struct
{
    CGFloat c[8];
} Components;


// declare and initialise in one go:
Components comps = {
    0.0, 0.0, 0.0, 0.0,
    0.0, 0.0, 0.0, 0.15
};


// declare and then assign:
Components comps;
comps = (Components){
    0.0, 0.0, 0.0, 0.0,
    0.0, 0.0, 0.0, 0.15
};


// To access elements:
comps.c[3] = 0.04;

If you use this approach, you can also return Components structs from methods, which means you can create functions to initialise and assign to the struct, for example:

Components comps = SomeFunction(inputData);

DoSomethingWithComponents(comps);

comps = GetSomeOtherComps(moreInput);

// etc.

Answer 3

That notation for arrays and structs is valid only in initializations, so no.