Are `typedef` and `struct` inside of a function standard in C?

I used some code like this:

void A()
{
    typedef struct B B;
    struct B
    {

    };

    B b;
};

typedef and struct definition inside a function. It compiled with Clang, but I want to know (1) whether they are part of standard or not. And about (2) whether they are开发者_C百科 limited to be recognized in function scope only.

---

Yes, the standard allows this, and yes, the name you create this way is only visible inside the function (i.e., it has local scope, just like when you define int i;, i has local scope).

It's more common, however to do it something like this:

typedef struct { 
    /* ... */ 
} B;
B b;

---

Yes it is allowed. but you cannot have
function inside a function.

declarations should be done first and later on you can do with your actual code.

you cannot declare after you do some operation inside your function like below

void A()
{

int a=0;

a++;    

typedef struct B B;//this is wrong
    struct B
    {

    };

    B b;
};