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When multiple statements are used in a macro, they should be bound together in a a do-while loop syntactically, so the macro can appear safely inside 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 a do-while loop. See EXP19-C. Use braces for the body of an if, for, or while statement.
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The problem is the semicolon (;
Compliant Solution
Wrapping the macro inside a a do-while loop mitigates the problem.
| Code Block | ||||
|---|---|---|---|---|
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/*
* Swaps two values.
* Requires tmp variable to be defined.
*/
#define SWAP(x, y) \
do { \
tmp = x; \
x = y; \
y = tmp; } \
while (0)
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The The do-while loop will always be executed exactly once.
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