EXP06-A. Operands to the sizeof operator should not contain side effects

The following program compiles cleanly under Microsoft Visual Studio 2005 Version 8.0, with the /W4 option:

int main(void) {
  int a = 14;
  int b = sizeof( a++ );
  printf("a, b = %d, %d.\n", a, b);  /* prints a, b = 14, 4. */
  return 0;
}

The indicated expression will be discarded; consequently, any side effects in that expression will not be executed.

In the example, the variable a will still have a value 14 after b has
been initialized.Whether or not a size expression is evaluated when it is part of the operand of a
sizeof operator and changing the value of the size expression would not affect the
result of the operator (6.7.5.2).