Mixing of two #defines into one word

Question

The convention of controls on my dialog is:

 #define DLG_NAME 1 #define DLG_NAME_CONTROL_NAME 2

I want to build a function which will know the control name, and has to get the defined value.
It's clear that I can't write int i = DLG_NAME + _ + CONTROL_NAME.

So how can I mix the first #define and another text to get the second #define value?

As chris suggested, you can use the ## operator to combine macro names. However, I do not understand what you want to achieve. Do you want to get 1_2 as an identifier ? (its is not a valid one). — Matthieu Rouget
– Matthieu Rouget, Commented May 30, 2013 at 8:19
No. I want the preprocessor will translate int i = DLG_NAME_CONTROL_NAME. — Aharon
– Aharon, Commented May 30, 2013 at 8:24
I'll explain better: I want to create some classes derived from common control class, and I'll write #define DLG_NAME_FIRST_COMBO 2 and #define CONTROL_NAME FIRST_COMBO, and in the class's function I'll write int i = DLG_NAME##CONTROL_NAME. Each class will operate it as defined in it. Am I right? — Aharon
– Aharon, Commented May 30, 2013 at 8:46

Matthias · Accepted Answer · 2013-05-30 09:16:29Z

I guess, what you are looking for is:

#define DLG_NAME_FIRST_COMBO 2 #define CONTROL_NAME(x) DLG_NAME_##x int i = CONTROL_NAME(FIRST_COMBO);

The way you suggested in your comment does not work, since the macro expression is not re-evaluated outside a definition.

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