The following code generates a this error when compiled: C51 COMPILER V6.02 - SN: XXXXX-XXXXX COPYRIGHT KEIL ELEKTRONIK GmbH 1987 - 1999 *** ERROR C221 IN LINE 7 OF QUEUE_I.H: non-constant case/dim expression
const unsigned char code BUF_SIZE = 40; BYTE Qbuf[BUF_SIZE];
#define BUF_SIZE 40
Your problem is that your "constant" isn't actually a constant. It's a variable flagged "const", which is a rather different thing. The only other major alternative to #define to create an actual constant (what the C standard calls a "compile-time constant expression") is to make it an enum label, i.e.
enum {BUF_SIZE = 40};
I was surprised since other compilers compiled the const version without errors (GNU X-Tools for one). In addition, I've read Good Style practices that recommended using const rather than #define, so I wouldn't expect using it to violate ANSI C rules.
"I was surprised since other compilers compiled the const version without errors (GNU X-Tools for one)." I you sure that they were all 'C' compilers - not C++? Also, are you sure that you tried this in their strict ANSI mode? "In addition, I've read Good Style practices that recommended using const rather than #define" Again, are you sure they were specifically for 'C' - rather than C++, or any other language?
Both probably weren't strict ANSI C, but the compiler wasn't a C++ compiler nor was the style guideline for C++.
In addition, I've read Good Style practices that recommended using const rather than #define Then get back to whoever wrote them and challenge them about this aspect --- they must either be talking about programming languages similar in syntax to C, but different (Java or C++, e.g.), or they simply don't know what the heck they're talking about, and should refrain from handing out advice to others. The loop-hole that let GCC compile this code is that it (and the C99 standard now, too) allow variable-size arrays. But for most practical purposes, good C programming style these days is still based on C89+addenda, not C99.