Understanding the usage of a variable as an array size in C

Question

I'm trying to understand the difference that the scoping makes:

//global scope
int size = 4;
int array[size]; // error: variably modified 'array' at file scope

int main(void) {
  int buff[size]; // works!
}

how does using a variable as array size doesn't work globally but works inside main? It would work if I use a macro instead.

Also, does using const matter for size?

in c89 ansic the size of the array must be declared as leteral (in define or just a number). this code will not compiled in c89 — Adam, May 23 '20 at 17:59
https://stackoverflow.com/questions/50858475/define-array-globally-with-variable-parameter-in-c maybe you are looking for this. — Harsh Kumar Jangir, May 23 '20 at 18:04
Does this answer your question? [declaring a variable-length array as a global variable in C](https://stackoverflow.com/questions/10360394/declaring-a-variable-length-array-as-a-global-variable-in-c) — Soma, May 23 '20 at 18:05
@adam Any particular reason for referring to C89 instead of C99, C11 or C18? OP's code works for `main(void)`, so OP much be using C99 or later. — chux - Reinstate Monica, May 23 '20 at 18:11

score 0 · Answer 1 · answered May 23 '20 at 18:02

0

simply make it compile time integral constant expression, since array length must be specified at the compile time, with define

#define SIZE   6

int array[SIZE];

answered May 23 '20 at 18:02

Adam

1

but how come it works in `main`? – xyf May 23 '20 at 18:04
please write here the compilation flags (or the compilation line you have used) – Adam May 23 '20 at 18:06
check this: https://cplayground.com/?p=bird-echidna-sandpiper – xyf May 23 '20 at 18:13

1 Answers1