Question

Consider a C struct:

struct T {     int x;     int y; }; 

When this is partially initialized as in

struct T t = {42}; 

is t.y guaranteed to be 0 or is this an implementation decision of the compiler?

Answer 1

item 8.5.1.7 of standard draft:

-7- If there are fewer initializers in the list than there are members in the aggregate, then each member not explicitly initialized shall be default-initialized (dcl.init). [Example:

struct S { int a; char* b; int c; }; S ss = { 1, 'asdf' }; 

initializes ss.a with 1, ss.b with ‘asdf’, and ss.c with the value of an expression of the form int(), that is, 0. ]