Function-like macro definition

Reports a #define whose name is immediately followed by a parameter list, that is, a function-like macro. An object-like macro such as #define TIMEOUT (30 * 1000), where a space separates the name from the parenthesis, is not reported.

A function-like macro is expanded by the preprocessor as raw text, so it has no types, no scope and no single evaluation of its arguments. An argument with a side effect is evaluated once per textual occurrence, a missing pair of parentheses silently changes operator precedence at the call site, and a multi-statement body breaks when used as the body of an unbraced if. None of this is visible to the compiler’s type checker, to the debugger, or to a reader of the call site, which makes the resulting defects hard to find.

The following code illustrates the pattern detected by this rule:

Replace the macro with a static inline C function or an Objective-C method, which gives the compiler real parameter types and evaluates each argument exactly once. Where a compile-time constant is all that is needed, use static const or an NS_ENUM. If a macro is genuinely unavoidable, parenthesize every parameter and the whole body, and use each parameter once.

This detector does not need any configuration.