Can you explain the macro processing mechanism in code preprocessing?

Macros in C/C++ are preprocessor directives that are processed before the code is compiled. The preprocessor replaces all occurrences of a macro with a specified value or code, allowing the creation of constants, inline functions, or conditional code inclusion.

Example of a simple macro:

#define PI 3.14

float circle_area(float r) {
    return PI * r * r;
}

Here, during preprocessing, all instances of PI will be replaced with 3.14. This helps avoid computational costs at runtime and makes the code easier to maintain.

Macros can be:

• Object-like (replace an identifier with text)
• Function-like (accept parameters and substitute them into the macro body)

It is important to remember that macros are not checked by the compiler for types, which can lead to errors if used improperly.