Added nxt_sizeof_array() to safely use sizeof() on arrays.

This macro is just sizeof(array), with compiler warnings for when the
input is not an array.  nxt_nitems() will trigger -Wsizeof-pointer-div
when the input is not an array.  The multiplication by 0 is to ignore
the result of nxt_nitems(), which we only want for the warning.

/*
 * SYNOPSIS
 *      size_t sizeof_array(array);
 *
 * ARGUMENTS
 *      array   Array to be sized.
 *
 * DESCRIPTION
 *      Measure the size of an array --equivalent to sizeof(array)--.
 *      This macro has the benefit that it triggers the warning
 *      '-Wsizeof-pointer-div' when the argument is a pointer instead
 *      of an array, which can cause subtle bugs, sometimes impossible
 *      to detect through tests.
 *
 * EXAMPLES
 *      int     *p;
 *      int     a[1];
 *      size_t  sp, sa;
 *
 *      sp = sizeof_array(p);  // Warning: -Wsizeof-pointer-div
 *      sa = sizeof_array(a);  // OK
 *
 * SEE ALSO
 *      <https://stackoverflow.com/questions/37538/how-do-i-determine-the-size-of-my-array-in-c/57537491#57537491>
 */

Signed-off-by: Alejandro Colomar <alx@nginx.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/src/nxt_clang.h b/src/nxt_clang.h
index 94638346..919d9168 100644
--- a/src/nxt_clang.h
+++ b/src/nxt_clang.h
@@ -251,6 +251,10 @@ nxt_popcount(unsigned int x)
     (u_char *) ((uintptr_t) (p) & ~((uintptr_t) (a) - 1))
 
 
+#define nxt_sizeof_array(a)                                                   \
+    (sizeof(a) + (0 * nxt_nitems(a)))
+
+
 #define nxt_length(s)                                                         \
     (sizeof(s) - 1)