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This noncompliant solution attempts to modify a variable's value as part of the _Generic association list. The user may have expected the value of a to be 2 because the type of the variable is int, but because _Generic does not evaluate its operands, the result is undefined behaviorthe value of a is not modified.

#define S(val) _Generic(val, int : val = 2, \
                             short : val = 3, \
                             default : val = 1)
void func(void) {
  int a = 0;
  S(a);
}

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This noncompliant code example attempts to modify a variable while getting its default alignment value. The user may have expected val to be incremented as part of the _Alignof expression, but because _Alignof does not evaluate its operand, the result val is undefined behaviorunchanged.

#include <stddef.h>
 
void func(void) {
  int val = 0;
 
  /* ... */
 
  size_t align = _Alignof(++val);
 
  /* ... */
}

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