Re: Hello, I have a problem with CPP here
taozhijiang <taozhijiang@gmail.com> writes:
> I want to using #define / #undef, and want to put them in a single
> macro, some thing like:
> #define DECALRE_TYPE(type) \
> { #undef __curr_type; #define _curr_type type; }
> as we know, this can not passed with CPP, but I need this logical here.
I'm afraid the answer is that you can't do that, since it's not part of
the C programming language. You can't use macro parameters in #define
that way because #define processing happens at too early of a stage in the
compilation process.
> Generally, the problem comes from
> #define ser_field(type, var) \
> ser_new_field(tra, #type, #var, offsetof(struct_type, var))
> I do not want another additional parameter in this macro like
> #define ser_field(type,var,struct_type), and I want a sentence declare
> "current struct type"
> and all later work of ser_field will defaultly use this type.
You can #undef and then #define the ser_field macro with a different
struct_type. I think that's the best solution you'll be able to get while
using only the C preprocessor.
--
Russ Allbery (rra@debian.org) <http://www.eyrie.org/~eagle/>
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