Found on MSDN
A Microsoft C extension allows you to declare a structure variable within another structure without giving it a name. These nested structures are called anonymous structures. C++ does not allow anonymous structures.You can access the members of an anonymous structure as if they were members in the containing structure.
// anonymous_structures.c #include struct phone { int areacode; long number; }; struct person { char name[30]; char gender; int age; int weight; struct phone; // Anonymous structure; no name needed } Jim; int main() { Jim.number = 1234567; printf_s("%d\n", Jim.number); }