Linux Format forums

[tedius]

I'm trying to write a macro that will call a function to copy some values.
The extract below is only a small part of my program but I hope it will give you the idea of what I'm trying to do.

[vorian]

Macros are evaluated by the preprocessor not the core compiler. You should treat it like string substitution.
After the preprocessing stage your code looks like:
for (i = 1; i <= 3; i++)
copyAtt((dest)->att_i, \
list,
i);
now the core compiler gets to work and seeks to find a att_i attribute (there is none ).

[jjmac]

Thats a really good problem

But, as suggested above ... the preprocessor can only reall do a compile-time substitution. And it will require a 'constant' to use in the substitution.

Where as, your looking for a run-time evaluation. I don't think the preprocessor can do that.

You would need to provide some trick to allow for a 'constant' to be passes, like the below.

[tedius]

Thanks for the help guys.

I had sort of come to the conclusion that what I was trying was not going to work

The solution that I am using is just to remove it from the loop and do one line for each copy. It works, but with 34 attributes to copy I was hoping for something more cleaver.

jjmac.

The reason I didn't use a vector is that the struct that I'm coping to is already define, and I don't have control over it

[jjmac]

>>
The reason I didn't use a vector is that the struct that I'm coping to is already define, and I don't have control over it
>>

Arrha, i see

The "switch" will work though, it's just that the preproccesor will need a const at compile-time, for the substitution.


jm
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