SEI CERT C Coding Standard

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This CUBE() macro definition is non-compliant because it fails to parenthesize the variable names.

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#define CUBE(I) (I * I * I)
int a = 81 / CUBE(2 + 1);

As a result, the invocation

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int a = 81 / CUBE(2 + 1);

expands to

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int a = 81 / (2 + 1 * 2 + 1 * 2 + 1);  /* evaluates to 11 */

while the desired behavior is

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int a = 81 / ( (2 + 1) * (2 + 1) * (2 + 1)); /* evaluates to 3 */

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Parenthesizing all variable names in the CUBE() macro allows it to expand correctly (when invoked in this manner).

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#define CUBE(I) ( (I) * (I) * (I) )
int a = 81 / CUBE(2 + 1);

However, if a parameter appears several times in the expansion, the macro may not work properly if the actual argument is an expression with side effects. Given the CUBE() macro above, the invocation

Code Block
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int a = 81 / CUBE(i++);

expands to

Code Block
int 
...
 a 
...
 = 
...
 81 
...
 / 
...
 (i++ 
...
 * 
...
 i++ 
...
 * 
...
 i++);


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 Wiki Markup
which is undefined (see \[[EXP30|EXP30-C. Do not depend on order of evaluation between sequence points]\]).
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