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C Macros

This lesson is part of C · All levels

Summary

Macro is a text substitution performed by a preprocessor before compilation and written with #define. A simple object macro such as #define PI 3.14159, whereas a function macro uses parameters such as #define MAX(a,b) ((a) > (b)? (a): (b)). Because it's just a substitution of text, macros are vulnerable when an expression is not encapsulated or the argument has side effects.

Key points

The preprocessor replaces the macro before compilation starts, so no variables or types are created.
Wrap the entire macro result and every argument in the bracket so that the order of operations remains true.
Avoid side-effect arguments such as MAX(i++, 5) as they can be evaluated more than once.
Use enum, inline, or ordinary functions when possible because it is safer than macro.
Macros are also used to include guard and conditional compilation with #ifdef.

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