text: #include <ccan/container_of/container_of.h>
  #include <stdlib.h>
  
  struct foo {
  	int a;
  	char b;
  };
  
  int main(int argc, char *argv[])
  {
  	struct foo foo = { .a = 1, .b = 2 };
  	int *intp = &foo.a;
  	char *p;
  
  #ifdef FAIL
  	/* p is a char *, but this gives a struct foo * */
  	p = container_of(intp, struct foo, a);
  #else
  	p = (char *)intp;
  #endif
  	return p == NULL;
  }
  