From: Francis Deslauriers Date: Tue, 3 Apr 2018 20:24:49 +0000 (-0400) Subject: Silence unused variable warnings caused by BT_ASSERT() in non-debug mode X-Git-Url: http://git.efficios.com/?p=babeltrace.git;a=commitdiff_plain;h=d7da1f66c46f7fa93ec4d70a889f9274e06f472e Silence unused variable warnings caused by BT_ASSERT() in non-debug mode When building with the BABELTRACE_DEBUG_MODE configure option _not_ set, multiple set-but-not-used warnings are emitted by the compiler. Most of the time this happens because BT_ASSERT() is used to verify the return value of functions and when not in DEBUG_MODE those return value are not used. The solution is to explicitly tell the compiler that we don't care about this value so that it does not emit warning when building in non-debug mode. This approach also makes sure not to evaluate the expression using the `sizeof` operator, thus preventing any side effects. See this post for further details [1]. [1]: https://stackoverflow.com/questions/37411809/how-to-elegantly-fix-this-unused-variable-warning/37412551#37412551 Signed-off-by: Francis Deslauriers --- diff --git a/include/babeltrace/assert-internal.h b/include/babeltrace/assert-internal.h index c8a9f837..5d78f96f 100644 --- a/include/babeltrace/assert-internal.h +++ b/include/babeltrace/assert-internal.h @@ -39,7 +39,17 @@ */ # define BT_ASSERT_FUNC #else -# define BT_ASSERT(_cond) +/* + * When BT_DEBUG_MODE is not defined, define BT_ASSERT() macro to the following + * to trick the compiler into thinking that the variable passed as condition to + * the assertion is used. This is to prevent set-but-not-used warnings from the + * compiler when assertions are disabled. The `sizeof` operator also makes sure + * that the `_cond` expression is not evaluated, thus preventing unwanted side + * effects. + * + * In-depth explanation: https://stackoverflow.com/questions/37411809/how-to-elegantly-fix-this-unused-variable-warning/37412551#37412551 + */ +# define BT_ASSERT(_cond) ((void) sizeof((void) (_cond), 0)) # define BT_ASSERT_FUNC __attribute__((unused)) #endif /* BT_DEBUG_MODE */