Re: preprocessor question

From:

Maxim Yegorushkin <maxim.yegorushkin@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Mon, 1 Dec 2008 08:34:24 -0800 (PST)

Message-ID:

<a234f9e6-c7ce-4719-b3c1-c18981a30f67@g38g2000yqn.googlegroups.com>

On Dec 1, 3:16 pm, David Resnick <lndresn...@gmail.com> wrote:

Given this code fragment:

#define IFV(func, number) \
incomingFunctVal<CVxicBridgedXferIncomingAction> val##num=

ber

( \
number, &CVxicBridgedXferIncomingAction::func); \
m_transFnMap.insert(fnMap::value_type(#func, val##number)=

);

        IFV( DoJoin, 1 );
        IFV( DoJoinRestartReco, 2 );
        IFV( DummyAction, 3 );
        IFV( RestartReco, 4 );
        ....
        IFV( SomeFunc, 100 );

I'm wondering if there is a way to have the numbers in the function
macro increment automatically?

You could use __COUNTER__ macro. If it is supported by your compiler.

Otherwise, draw inspiration from boost preprocessor library:
http://www.boost.org/doc/libs/1_37_0/libs/preprocessor/doc/ref/counter.html

The code in the macro isn't really subject to change (it is the way to
use a state machine
implementation that I can't modify).

That's too bad, since such an interface is real pain.

I wonder why incomingFunctVal<> constructor needs that integer? If it
can be auto-generated (possibly in incomingFunctVal<> constructor) by
incrementing a global or class static variable, and if you don't
really need valN objects (their copies are stored in m_transFnMap
anyway) the macro could be simplified to:

    typedef CVxicBridgedXferIncomingAction X; // for brevity
    int x = 0; // the global counter

    #define IFV(func) \
    m_transFnMap.insert( \
        fnMap::value_type( \
              #func \
            , incomingFunctVal<X>(++x, &X::func) \
            ) \
        );

--
Max