Question

The idea is to create automatic caster which would paste pointer to the variable based on given prefix and number.
Lets say you have some interface which is continously developed so you get some new structure versions every couple of weeks. So instead of writing explicity “(structure1*), (structure2*)” and so on you could just use SOME_DEFINE(thisStructure, version); which would handle the case

I thought that this would do the trick

#define d1(x) x
#define d2(x,y) x##y

void someFunction()
{
    int temp = 3;
    d2(myStructure,d1(temp)) *thisStruct;
}

i was hoping that preprocessor would nest itself and paste d1 operation first and then merge result of d1 operation with first d2 argument. However it doesnt work, so my question is, how can i achive this cause it seems to be possible.

Answer 1

#define d2(x,y) x ## y

void someFunction()
{
    int temp = 3;
    d2(myStructure,temp) *thisStruct;
}

The preprocessor converts this to:

void someFunction()
{
    int temp = 3;
    myStructuretemp *thisStruct;
}

If you want to replace the ‘3’ in there so you get myStructure3, then you cannot do that with the preprocessor – it doesn’t know anything about C/C++ variables or their values.