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Macros can be used to execute a sequence of multiple statements as group.

In the event that multiple statements in a macro is not bound in a do-while loop (see Note that the following macro violates PRE10-C. Wrap multi-statement macros in a do-while loop), an if statement with opening and closing braces will still ensure that all statements of the macro are properly executed.

/*
 * Swaps two values.
 * Requires tmp variable to be defined.
 */
#define SWAPDEC(x, y) \
  tmp =printf("Initial value was %d\n", x); \
  x -= y; \
  printf("Current value y = tmpis %d\n", x)

This macro will expand correctly in a normal sequence of statements, but not as the then-clause in an if statement:

int x, y, z, tmp;

if (z == 0)
  SWAPDEC( x, y);

This will expand to:

int x, y, z, tmp;

if (z == 0)
  tmp =printf("Initial value was %d\n", x);
x -= y;
y = tmpprintf("Current value is %d\n", x);

Compliant Solution

Given an if statement bounded with opening and closing braces, the macro would expand as intended.

int x, y, z, tmp;

if (z == 0) {
  printf("Initial value tmp =was %d\n", x);
  x -= y;
  y = tmp;printf("Current value is %d\n", x)
}

Risk Assessment

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