Lesson 7 - Macros

A macro is a snippet of code that is assigned an identification string. If anywhere in the code the preprocessor encounters this string, it replaces it with the content of the given macro - i.e. macro expansion.

(author's note: the preprocessor starts before the compilation itself and replaces all macros in the source file with their contents).

In general, macros can be divided into two groups. The first group are macros without parentheses. These types of macros are used to define constants, characters, or strings. Macros with parentheses are usually used where we want to replace the macro with a function or a block of one or more lines of code, which can, for example, calculate the maximum value of two elements. At the same time, as with the classic function, it's possible to insert one or more parameters in parentheses.

Because the macro name is directly replaced by a block of code at the point of use, it doesn't load the CPU. Conversely, when calling a function, it's necessary to switch the context of the currently processed function and at the same time create a data structure called frame on the stack. These are operations that cost a certain amount of computational time.

(author's note: switching the context can mean, for example, backing up the registers available on a given microcontroller or processor).

Rules for using macros

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