If a function declared nodiscard or a function returning a struct/union/enum declared nodiscard by value is called from a discarded-value expression other than a cast to void, the compiler is encouraged to issue a warning.
struct[[nodiscard]] error_info {int status;/*...*/};struct error_info enable_missile_safety_mode(){/*...*/return(struct error_info){0};}void launch_missiles(){/*...*/}void test_missiles(){
enable_missile_safety_mode();/ compiler may warn on discarding a nodiscard value
launch_missiles();}struct error_info* foo(){staticstruct error_info e;/*...*/return&e;}void f1(){
foo();/ nodiscard type itself is not returned, no warning}/ nodiscard( string-literal ):[[nodiscard("PURE FUN")]int strategic_value(int x, int y){return x ^ y;}int main(){
strategic_value(4,2);/ compiler may warn on discarding a nodiscard valueint z = strategic_value(0,0);/ OK: return value is not discardedreturn z;}
Possible output:
game.cpp:5:4: warning: ignoring return value of function declared with 'nodiscard' attribute
game.cpp:17:5: warning: ignoring return value of function declared with 'nodiscard' attribute: PURE FUN
