Attributes
__attribute__((error("message")))Declare that calling the marked function is an error.
__attribute__((warning("message")))Declare that calling the marked function is suspect and should emit a warning.
__attribute__((deprecated))Declare that using the marked function, type, or variable is deprecated and will emit a warning.
__attribute__((const))Declare that the marked function is a pure function, only examining its arguments and returning a value without examining or changing anything else.
__attribute__((pure))Declare that the marked function is a pure function, with no side effects (although it may examine global state).
__attribute__((nonnull(n1...)))Declare that the specified arguments (one-based) (or all arguments if no indexes are listed) should only be passed nonnull pointers.
__attribute__((noreturn))Declare that the marked function will not return (although it may throw).
__attribute__((hot))Hint that the marked function is "hot" and should be optimized more aggresively and/or placed near other "hot" functions (for cache locality).
__attribute__((cold))Hint that the marked function is "cold" and should be optimized for size, predicted as unlikely for branch prediction, and/or placed near other "cold" functions (so other functions can have improved cache locality).
__attribute__((warn_unused_result))Declare that the function's return value is important and should be warned about if ignored.
Miscellaneous
case low ... high:Case branch with a range.
0bbinary-digitsBinary constant.