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cconstantsstatic-array

Static arrays with variable length

Is the following legal?

const int n=10;
static int array[n];

If, yes, then why and how?

Solution

  • Note that in C language const objects do not qualify as constants. They cannot be used to build constant expressions. In your code sample n is not a constant in the terminology of C language. Expression n is not an integral constant expression in C.

    (See "static const" vs "#define" vs "enum" and Why doesn't this C program compile? What is wrong with this? for more detail.)

    This immediately means that your declaration of array is an attempt to declare a variable-length array. Variable length arrays are only allowed as automatic (local) objects. Once you declare your array with static storage duration, the size must be an integral constant expression, i.e. a compile-time constant. Your n does not qualify as such. The declaration is not legal.

    This is the reason why in C language we predominantly use #define and/or enum to introduce named constants, but not const objects.