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The arguments to a macro must not include preprocessor directives, such as #define, #ifdef, and #include. Doing so results in undefined behavior, according to the C Standard, 6.10.3, paragraph 11 [ISO/IEC 9899:2011]:

The sequence of preprocessing tokens bounded by the outside-most matching parentheses forms the list of arguments for the function-like macro. The individual arguments within the list are separated by comma preprocessing tokens, but comma preprocessing tokens between matching inner parentheses do not separate arguments. If there are sequences of preprocessing tokens within the list of arguments that would otherwise act as preprocessing directives, the behavior is undefined.

See also undefined behavior 93.

This rule also applies to the use of preprocessor directives in arguments to a function where it is unknown whether or not the function is implemented using a macro. For example, standard library functions, such as memcpy(), printf(), and assert(), may be implemented as macros.

Noncompliant Code Example

In this noncompliant code example [GCC Bugs], the programmer uses preprocessor directives to specify platform-specific arguments to memcpy(). However, if memcpy() is implemented using a macro, the code results in undefined behavior.

#include <string.h>
 
void func(const char *src) {
  /* Validate the source string; calculate size */
  char *dest;
  /* malloc() destination string */ 
  memcpy(dest, src,
    #ifdef PLATFORM1
      12
    #else
      24
    #endif
  );
  /* ... */
}

Compliant Solution

In this compliant solution [GCC Bugs], the appropriate call to memcpy() is determined outside the function call:

#include <string.h>

void func(const char *src) {
  /* Validate the source string; calculate size */
  char *dest;
  /* malloc() destination string */ 
  #ifdef PLATFORM1
    memcpy(dest, src, 12);
  #else
    memcpy(dest, src, 24);
  #endif
  /* ... */
}

Risk Assessment

Including preprocessor directives in macro arguments is undefined behavior.

Rule

Severity

Likelihood

Remediation Cost

Priority

Level

PRE32-C

Low

Unlikely

Medium

P2

L3

Automated Detection

Tool

Version

Checker

Description

Astrée
19.04
macro-argument-hashFully checked
Axivion Bauhaus Suite

6.9.0

CertC-PRE32Fully implemented
CodeSonar
5.1p0
LANG.PREPROC.MACROARGPreprocessing directives in macro argument

ECLAIR

1.2

CC2.PRE32

Fully implemented

LDRA tool suite
9.7.1
341 SFully implemented
Parasoft C/C++test

10.4.2

CERT_C-PRE32-a
Arguments to a function-like macro shall not contain tokens that look like preprocessing directives

Polyspace Bug Finder

R2018a

Preprocessor directive in macro argumentYou use a preprocessor directive in the argument to a function-like macro
PRQA QA-C
9.5
0853
PRQA QA-C++

4.3

1072 


RuleChecker
19.04
macro-argument-hashFully checked

Related Vulnerabilities

Search for vulnerabilities resulting from the violation of this rule on the CERT website.

Bibliography

[GCC Bugs]"Non-bugs"
[ISO/IEC 9899:2011]6.10.3, "Macro Replacement"