lib/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  *      #include <stddef.h>
  13  *      ...
  14  *      static char *foo_to_char(struct foo *foo)
  15  *      {
  16  *              // This code needs string to be at start of foo.
  17  *              BUILD_ASSERT(offsetof(struct foo, string) == 0);
  18  *              return (char *)foo;
  19  *      }
  20  */
  21 #define BUILD_ASSERT(cond) \
  22         do { (void) sizeof(char [1 - 2*!(cond)]); } while(0)
  23
  24 /**
  25  * BUILD_ASSERT_OR_ZERO - assert a build-time dependency, as an expression.
  26  * @cond: the compile-time condition which must be true.
  27  *
  28  * Your compile will fail if the condition isn't true, or can't be evaluated
  29  * by the compiler.  This can be used in an expression: its value is "0".
  30  *
  31  * Example:
  32  *      #define foo_to_char(foo)                                        \
  33  *               ((char *)(foo)                                         \
  34  *                + BUILD_ASSERT_OR_ZERO(offsetof(struct foo, string) == 0))
  35  */
  36 #define BUILD_ASSERT_OR_ZERO(cond) \
  37         (sizeof(char [1 - 2*!(cond)]) - 1)
  38
  39 #endif /* CCAN_BUILD_ASSERT_H */