CODEWITHSUNDEEP
c++preprocessor-directive
Barney Szabolcs
Barney Szabolcs

Reputation: 12544

Can I create other #define's with a preprocessor function?

I know I will be punished after asking this, still I'd like to do something like this:

#define DEF_CLASS(x) \ 
  #define CLASS x \
  #define CONSTRUCTOR CLASS::CLASS \
  #define COPY_CONSTRUCTOR(x) CONSTRUCTOR(const CLASS& x)

That is I'd like to have a "#define" function which dynamically defines other "#defines".

I have an IDE which is not capable of refactoring, furthermore I'd like to make constructors, especially copy constructor to stand out due to its special role.
Therefore I aim to program my c++ class definitions like this:

CONSTRUCTOR(int i):i(i){}
COPY_CONSTRUCTOR(other):i(other.i){}
void CLASS::fun1()
{
  //...
}

For that, currently I need to copy&paste three #define lines. I would rather do those automatically. Is there any way to pull this off using the preprocessor?

Upvotes: 1

Views: 511

Answers (2)

John Kugelman
John Kugelman

Reputation: 362087

No, such a DEF_CLASS(x) macro is not possible. Macros aren't stateful. The best you can do is:

#define CONSTRUCTOR CLASS::CLASS
#define COPY_CONSTRUCTOR(x) CONSTRUCTOR(const CLASS& x)

...

#define CLASS X
    CONSTRUCTOR(int i):i(i){}
    COPY_CONSTRUCTOR(other):i(other.i){}
    void CLASS::fun1()
    {
      //...
    }
#undef CLASS

#define CLASS Y
    CONSTRUCTOR(int i):i(i){}
    COPY_CONSTRUCTOR(other):i(other.i){}
    void CLASS::fun1()
    {
      //...
    }
#undef CLASS

But I strongly urge you not to abuse the preprocessor like this. Why obfuscate the normal C++ syntax with these macros? Accept C++ for what it is; don't try to make it into a different, friendlier language.

Upvotes: 1

Jerry Coffin
Jerry Coffin

Reputation: 490653

No -- §16.3.4/3:

The resulting completely macro-replaced preprocessing token sequence is not processed as a preprocessing directive even if it resembles one [...]

Upvotes: 2

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