struct instantiation with "struct" keyword

Question

Suppose I declare a new C++ struct type:

struct my_struct {
   int a;
   int b;
};

Can I create a new instance of this struct type by:

my_struct foo;

or

struct my_struct foo;

If both work, is there any difference?

Answer 1

Yes, you can use either method. The difference is that this form:

my_struct foo;

Is not legal in C, so you must use this form:

struct my_struct foo;

Which is supported in C++ for backwards compatibility with C.

Answer 2

Both work. The main reason the second works is compatibility with C: In C the first doesn't work. As a result, structs are typically typedefed in C and there are two different kinds of names for structs and typedefs.