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Macros are often used to execute a sequence of multiple statements as a group.

While inline Inline functions are, in general, more suitable for this task. (see See guideline PRE00-C. Prefer inline or static functions to function-like macros.) Occasionally, however, occasionally they are not feasible (when macros are expected to operate on variables of different types, for example).

When multiple statements are used in a macro, they should be bound together in a do-while loop syntactically, so the macro can appear safely inside if clauses or other places that expect a single statement or a statement block. (Alternatively, when an if, for or while statement uses braces even for a single body statement, then multiple statements in a macro will expand correctly even without a do-while loop. See guideline EXP19-C. Use braces for the body of an if, for, or while statement.)

Noncompliant Code Example

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int x, y, z, tmp;
if (z == 0)
  tmp = x;
x = y;
y = tmp;

which This is certainly not what the programmer intended.

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

Other Languages

Related Guidelines

This rule appears in the C++ Secure Coding Standard as : PRE10-CPP. Wrap multi-statement macros in a do-while loop.

Bibliography

\[[ISO/IEC PDTR 24772|AA. Bibliography#ISO/IEC PDTR 24772]\] "NMP Pre-processor Directions"
[Linux Kernel Newbies FAQ|http://kernelnewbies.org/FAQ] [FAQ/DoWhile0|http://kernelnewbies.org/FAQ/DoWhile0]

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