kaetzacoatl kaetzacoatl - 3 months ago 9
C Question

How to initialize only few elements of an array with some values?

This might be a stupid question, but is it possible to assign some values to an array instead of all? To clarify what I want:

If I need an array like

{1,0,0,0,2,0,0,0,3,0,0,0}
I can create it like:

int array[] = {1,0,0,0,2,0,0,0,3,0,0,0};


Most values of this array are '0'. Is it possible to skip this values and only assign the values 1, 2 and 3? I think of something like:

int array[12] = {0: 1, 4: 2, 8: 3};

Answer

Is it possible to skip this values and only assign the values 1, 2 and 3?

In C, Yes. Use designated initializer (added in C99 and not supported in C++).

int array[12] = {[0] = 1, [4] = 2, [8] = 3};  

Above initializer will initialize element 0, 4 and 8 of array array with values 1, 2 and 3 respectively. Rest elements will be initialized with 0. This will be equivalent to

 int array[12] = {1, 0, 0, 0, 2, 0, 0, 0, 3, 0, 0, 0};   

The best part is that the order in which elements are listed doesn't matter. One can also write like

 int array[12] = {[8] = 3, [0] = 1, [4] = 2}; 

But note that the expression inside [ ] shall be an integer constant expression.

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