Best define questions in October 2010

Why do most C developers use define instead of const?

Asked on Tue, 26 Oct 2010 by C. Ross c coding-style define
43 votes

In many programs a #define serves the same purpose as a constant. For example.

#define FIELD_WIDTH 10
const int fieldWidth = 10;

I commonly see the first form preferred over the other, relying on the pre-processor to handle what is basically an application decision. Is there a reason for this tradition?

Answered by Bart van Ingen Schenau

There is a very solid reason for this: const in C does not mean something is constant. It just means a variable is read-only.

In places where the compiler requires a true constant (such as for array sizes for non-VLA arrays), using a const variable, such as fieldWidth is just not possible.