[metadata]
id = "PRE00-C"
type = "recommendation"
category = "PRE"
number = 0
title = "Prefer inline or static functions to function-like macros"
description = """
Macros are dangerous because their use resembles that of real functions, but
they have different semantics. The inline function-specifier was introduced to
the C programming language in the C99 standard. Inline functions should be
preferred over macros when they can be used interchangeably. Making a function
an inline function suggests that calls to the function be as fast as possible by
using, for example, an alternative to the usual function call mechanism, such
asinline substitution. (See alsoPRE31-C. Avoid side effects in arguments to
unsafe macros,PRE01-C. Use parentheses within macros around parameter names,
andPRE02-C. Macro replacement lists should be parenthesized.) Inline
substitution is not textual substitution, nor does it create a new function. For
example, the expansion of a macro used within the body of the function uses the
definition it had at the point the function body appeared, not where the
function is called; and identifiers refer to the declarations in scope where the
body occurs. Arguably, a decision to inline a function is a low-level
optimization detail that the compiler should make without programmer input. The
use of inline functions should be evaluated on the basis of (a) how well they
are supported by targeted compilers, (b) what (if any) impact they have on the
performance characteristics of your system, and (c) portability concerns. Static
functions are often as good as inline functions and are supported in C.
"""
severity = "Medium"
likelihood = "Unlikely"
priority = "P2"
level = "L3"
cert_version = "2016 Edition (Wiki)"
last_modified = "Oct 29, 2025"
[rules.cert_c.PRE00-C]
enabled = true
[references]
wiki = "https://wiki.sei.cmu.edu/confluence/display/c/PRE00-C.+Prefer+inline+or+static+functions+to+function-like+macros"