structure naming syntax

[johnmerlino]

I am looking at a linked list example, which uses structs:

typedef struct node {
    int val;
    struct node * next;
} node_t;

As you can see, we provide an optional name "node" that follows the word struct. And we can use "node" subsequently as a shorthand for the part of the declaration in braces.

But what is that node_t for? What is that doing?

[codewalker]

node_t is the resultant data type. So you can declare variable of type node_t like node_t *root

But this is C way of declaring a struct C++ way is

struct node_t {
    int val;
    node_t *next;
};

[johnmerlino]

Let's just confirm something, in C, when I do this:

node_t *root

that gets translated to:

struct root {
    int val;
    struct node * next;
} 

?

[MikeyBoy]

No. What you've posted would define a struct type called root.

node_t *root

creates a variable called root, whose type is a pointer to a struct node.

[doug4]

You have to look at this from the outside in.

The first statement you see is typedef <some type> node_t; This tells you that <some type> is being given an alias of node_t. That means that any time node_t is used in the code, it will refer to <some type>.

Before the alias can be assigned, the compiler has to first determine what the original type is that is being typedefed. Now we have to look at what <some type> is.

struct node {
    int val;
    struct node * next;
}

This is a named struct containing an int and a pointer to another one its own type. Because this struct is being defined before the definition of node_t is completed, the node_t alias cannot be used for the next pointer type. As a result, the full type name "struct node" must be used to define the type of the next pointer.

In C++ this no longer needs to be done. Because of different namespace handling in C++, we no longer need to specify "struct" when using a struct variable or pointer.

struct ABC
{
    int a;
    int b;
    int c;
};

C syntax:

struct ABC var1;
struct ABC *ptr = &var1;

C++ syntax:

ABC var1;
ABC *ptr = &var1;

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The typedef in C allowed C syntax to look more like C++ syntax before C++ existed.