Page History

...

This CUBE() macro definition is noncompliant because it fails to parenthesize the replacement list.:

#define CUBE(X) (X) * (X) * (X)
int i = 3;
int a = 81 / CUBE(i);

As a result, the invocation

int a = 81 / CUBE(i);

expands to

int a = 81 / i * i * i;

which evaluates as

int a = ((81 / i) * i) * i);  /* evaluatesEvaluates to 243 */

which is not the desired behavior.

...

With its replacement list parenthesized, the CUBE() macro expands correctly for this type of invocation.

#define CUBE(X) ((X) * (X) * (X))
int i = 3;
int a = 81 / CUBE(i);

...

In this noncompliant code example, EOF END_OF_FILE is defined as -1. The macro replacement list consists of a unary negation operator - followed by an integer literal 1.:

#define EOFEND_OF_FILE -1
/* ... */
if (getchar() EOFEND_OF_FILE) {
   /* ... */
}

In this example, the programmer has mistakenly omitted the comparison operator (see MSC02-C. Avoid errors of omission) from the conditional statement, which should be getchar() != EOF. END_OF_FILE. (See void MSC02-C. Avoid errors of omission.) After macro expansion, the conditional expression is incorrectly evaluated as a binary operation: getchar()-1. This statement is syntactically correct, even though it is certainly not what the programmer intended. Note that this example also violates DCL00-C. Const-qualify immutable objects.

Parenthesizing the -1 in the declaration of EOF END_OF_FILE ensures that the macro expansion is evaluated correctly.:

#define EOFEND_OF_FILE (-1)

Once this modification is made, the noncompliant code example no longer compiles because the macro expansion results in the conditional expression getchar() (-1), which is no longer syntactically valid. Note that there must be a space after EOF END_OF_FILE because, otherwise, it becomes a function-like macro (and one that is incorrectly formed , because -1 −1 cannot be a formal parameter).

...

In this compliant solution, the macro definition is replaced with an enumeration constant in compliance with DCL00-C. Const-qualify immutable objects. In addition, because EOF is a reserved macro defined in the <stdio.h> header, the compliant solution must also use a different indentifier in order to comply with DCL37-C. Do not declare or define a reserved identifier.

enum { EOFEND_OF_FILE = -1 };
/* ... */
if (getchar() != EOFEND_OF_FILE) {
   /* ... */
}

Exceptions

PRE02-C-EX1: A macro that expands to a single identifier or function call is not affected by the precedence of any operators in the surrounding expression, so its replacement list need not be parenthesized.

#define MY_PID getpid()

PRE02-C-EX2: A macro that expands to an array reference using the array-subscript operator [], or an expression designating a member of a structure or union object using either the member-access . or -> operators is not affected by the precedence of any operators in the surrounding expression, so its replacement list need not be parenthesized.

#define NEXT_FREE block->next_free
#define CID customer_record.account.cid
#define TOOFAR array[MAX_ARRAY_SIZE]

Risk Assessment

Failing to parenthesize macro replacement lists can cause unexpected results.

Automated Detection

...

Tool	Version	Checker	Description
Axivion Bauhaus Suite	Include Page Axivion Bauhaus Suite_V Axivion Bauhaus Suite_V	CertC-PRE02
CodeSonar	Include Page CodeSonar_V CodeSonar_V	LANG.PREPROC.MACROEND LANG.PREPROC.MACROSTART	Macro Does Not End With ) or } Macro Does Not Start With ( or {
ECLAIR	Include Page ECLAIR_V ECLAIR_V	CC2.PRE02	Fully implemented
Helix QAC	Include Page Helix QAC_V Helix QAC_V	C3409
Klocwork	Include Page Klocwork_V Klocwork_V	MISRA.DEFINE.BADEXP
LDRA tool suite	Include Page LDRA_V LDRA_V	77 S	Fully implemented
Parasoft C/C++test	Include Page Parasoft_V Parasoft_V	CERT_C-PRE02-a	Enclose in parentheses whole definition of a function-like macro
PC-lint Plus	Include Page PC-lint Plus_V PC-lint Plus_V	773, 973	Fully supported

Related Vulnerabilities

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

Other Languages

...

Related Guidelines

...

...

...

...

Bibliography

...

Image Added Image Added Image Added 9899:1999|AA. C References#ISO/IEC 9899-1999]\] Section 6.10, "Preprocessing directives," and Section 5.1.1, "Translation environment" \[[ISO/IEC PDTR 24772|AA. C References#ISO/IEC PDTR 24772]\] "JCW Operator precedence/Order of Evaluation", "NMP Pre-processor Directions" \[[Plum 85|AA. C References#Plum 85]\] Rule 1-1 \[[Summit 05|AA. C References#Summit 05]\] Question 10.1Image Removed      01. Preprocessor (PRE)       PRE03-C. Prefer typedefs to defines for encoding types