Symbolic Constants: How are they stored and what are their types?

Question

C++ allows you to use the #define preprocessor directive to define symbolic constants which the compiler will replace before compilation. My question is, how do compilers typically store these internally and do they have data types?

Answer 1

Strictly speaking, the compiler never sees constants declared with the #define preprocessor directive. These are handled on a textual substitution basis by the preprocessor. They do not have "types" in the C++ sense, since the preprocessor does not know anything about the C++ language semantics.

The preprocessor uses a straightforward text substitution strategy to resolve macros. For example, in the following code:

#define FIVE 5

int a = FIVE;

the compiler will see only:

int a = 5;

The symbol FIVE is gone from the source the compiler sees. Your compiler will have an option to run the preprocessor only; in GCC it is -E and in MSVC it is /E or /P. Using such an option, you can run your source through the preprocessor to see how it is changed.