What is the meaning of `struct X typedef` vs. `typedef struct X`?

Question

I have the following (working) code in an existing code base, used in include file that is shared between C and C++, compiling on MSVC (2010) and Windows DDK:

Answer 1

Disclaimer: This is not a technical but a practical answer. Refer to the other answers for technical matters. This answer reads opinionated and subjective but please bear with me while I try to explain the bigger picture.

struct is a strange beast because the stuff you put between the closing bracket } and the semicolon ; refers to the content inside or before those brackets. I know why that is, and grammatically it does make sense, but personally I find it very counter-intuitive as curly brackets usually mean scope:

Counter-intuitive examples:

// declares a variable named `foo` of unnamed struct type.
struct {
    int x, y;
} foo;

foo.x = 1;


// declares a type named `Foo` of unnamed struct type
struct {
    int x, y;
} typedef Foo;

Foo foo2;
foo2.x = 2;


// declares a type named `Baz` of the struct named `Bar`
struct Bar {
    int x, y;
} typedef Baz;

// note the 'struct' keyword to actually use the type 'Bar'
struct Bar bar;
bar.x = 3;
Baz baz;
baz.x = 4;

There are so many subtle things that can go wrong with the dense syntax of structs and typedefs if used like this. As shown below it is very easy to declare a variable instead of a type by accident. The compiler is only of limited help because almost all combinations are grammatically correct. They just don't necessarily mean what you try to express. It is a pit of despair.

Wrong examples:

// mixed up variable and type declaration
struct foo {
    int x, y;
} Foo;

// declares a type 'foo' instead of a variable
typedef struct Foo {
    int x, y;
} foo;

// useless typedef but compiles fine
typedef struct Foo {
    int x, y;
};

// compiler error
typedef Foo struct {
    int x, y;
};

For reasons of readability and maintenance I prefer to declare everything separately and never put anything behind the closing curly bracket. The cost of additional lines of code are easily outweighed by intuitive syntax. I argue that this approach makes it easy to do the right things and annoying to do the wrong things.

Intuitive examples:

// declares a struct named 'TVector2'
struct TVector2 {
    float x, y;
};

// declares a type named 'Vector2' to get rid of the 'struct' keyword
// note that I really never use 'TVector2' afterwards
typedef struct TVector2 Vector2;

Vector2 v, w;
v.x = 0;
v.y = 1;