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#include <stdio.h>
 
void func(void) {
  static volatile int **ipp;
  static int *ip;
  static volatile int i = 0;

  printf("i = %d.\n", i);

  ipp = &ip; /* Produces warnings in modern compilers */
  ipp = (int**) &ip; /* Constraint violation; also produces warnings */
  *ipp = &i; /* Valid */
  if (*ip != 0) { /* Valid */
    /* ... */
  }

}

The assignment ipp = &ip is unsafe because it would allow the valid code that follows to reference the value of the volatile object i through the non-volatile-qualified reference ip. In this example, the compiler may optimize out the entire if block because i != 0 must be false if i is not volatile.

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This example compiles without warning on Microsoft Visual Studio 2012 2013 when compiled in C mode (/TC) but causes errors when compiled in C++ mode (/TP).

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