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While inline functions are, in general, more suitable for this task (see PRE00-A. Prefer inline or static functions to function-like macros), occasionally they are not feasible . For instance, (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 loop syntactically, so the macro can appear safely inside if-clauses, or other places that expect a single statement or a statement 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 do-while loop will always be executed exactly once.
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