Re: [lwip-devel] [bug #35875] #define ⇒ enum?

[Bill Auerbach]

>-----Original Message-----
>On Behalf Of David Brown
>Sent: Monday, March 19, 2012 8:01 AM
>Subject: Re: [lwip-devel] [bug #35875] #define ⇒ enum?
>
>Using enum types for the values can cause warnings if you use a compiler
>and warnings that check for mixes between enumerated types and integers,
>or if you compile in forced C++ mode.  So while using enum types is good
>in some ways, it may mean extra explicit casts to make the code compile
>cleanly in all cases.

Although this is strictly true, in practice any decent compiler will not
promote a constant to an int if it is used in a way that allows the same
correct result by not promoting.  A compiler that can generate an 8-bit
compare of a char to a constant compare probably would do this (and IMO
isn't very good if it doesn’t).

I think on most compilers changing to enum will make the code size slightly
larger.  It should improve things in a debugger which (again if good) if it
will show the enum member name when viewing an enum variable.  I've seen a
compiler with a compiler option use an 8-bit enum when all of the members
fit in 8-bits - I don't know if any mainstream compilers do this.

>An alternative might be to use "static const u8_t" values rather than
>"#define" macros, but again there could be problems with warning-free
>compiles if the values are used in several places.

And a compiler is not prevented by the standard from created storage for
this IIRC.

Bill