c++ - Initializing union member in initializer list without narrowing -

in following code,

typedef unsigned long col24; inline col24 makergb24(int r, int g, int b) { return ...; }  struct blitdata {   union   {     int flags, stretch;     col24 luminance;   };   // (other members) };  int main() {   blitdata blitdata =   {     makergb24(0, 0, 0),     // ...   }; } 

why first initializer in initializer list of blitdata give following error:

non-constant-expression cannot narrowed type col24 (aka unsigned long) int in initializer list

why compiler trying initialize int member of union initializer type col24 instead of using initialize col24 member?

the compiler suggests static_cast result of makergb24 int, result in unwanted narrowing.

how can luminance member correctly initialized using result of makergb24 in initializer list?

edit: blitdata should stay pod.

this apparently nonstandard gcc extension, you're after:

blitdata blitdata = {     luminance: makergb24(0,0,0), }; 

if that's no you, suspect assigning afterwards way.