ccan/build_assert/build_assert.h

   1 #ifndef CCAN_BUILD_ASSERT_H
   2 #define CCAN_BUILD_ASSERT_H
   3
   4 /**
   5  * BUILD_ASSERT - assert a build-time dependency.
   6  * @cond: the compile-time condition which must be true.
   7  *
   8  * Your compile will fail if the condition isn't true, or can't be evaluated
   9  * by the compiler.  This can only be used within a function.
  10  *
  11  * Example:
  12  *      char *foo_to_char(struct foo *foo)
  13  *      {
  14  *              // This code needs string to be at start of foo.
  15  *              BUILD_ASSERT(offsetof(struct foo, string) == 0);
  16  *              return (char *)foo;
  17  *      }
  18  */
  19 #define BUILD_ASSERT(cond) \
  20         do { (void) sizeof(char [1 - 2*!(cond)]); } while(0)
  21
  22 /**
  23  * EXPR_BUILD_ASSERT - assert a build-time dependency, as an expression.
  24  * @cond: the compile-time condition which must be true.
  25  *
  26  * Your compile will fail if the condition isn't true, or can't be evaluated
  27  * by the compiler.  This can be used in an expression: its value is "0".
  28  *
  29  * Example:
  30  *      #define foo_to_char(foo)                                        \
  31  *               ((char *)(foo)                                         \
  32  *                + EXPR_BUILD_ASSERT(offsetof(struct foo, string) == 0))
  33  */
  34 #define EXPR_BUILD_ASSERT(cond) \
  35         (sizeof(char [1 - 2*!(cond)]) - 1)
  36
  37 #endif /* CCAN_BUILD_ASSERT_H */