q for the C hackers

[David Long]

> However, what is the convention in C?  There seem to be two fine ways 
> of doing it -- using the preprocessor, or the const keyword:
> 
> #define NUMBER_OF_UNITS 8
> 
> const int NUMBER_OF_UNITS = 8;
> 
> 
> 
> I'm just interested in hearing about whether one is more appropriate 
> than the other in some contexts.  Thanks.

I would stick with defines.  More modern languages have the option of
effectively treating a "const" declaration as an immediate value, but I
do not believe that C can.  However there are times when a declaration
which allocates storage is necessary, as when you need to pass a pointer
to a value.  Also, for strings the C standard requires each literal
string constant to occupy unique read/write storage (in case the code
decides to rewrite part of it).  Therefore allocating a (optionally
const) variable will use less storage than repeated use of a define'd
string constant.  Alternatively most compilers provide an option for
making string constants read-only.

The "const" type modifier is part of the ANSI/ISO C language standard
(as is "void" and various other post K&R enhancements).

-dl
-- 
David A. Long
JumpShift, LLC

dave at jumpshift.com