函数返回类型返回结构指针的编译器抛出错误

Question

Can someone please explain why am I getting the compilation error the below code.

Error says:

"expected unqualified-id before 'struct' " on line number 7 ".

My code:

struct node{
    int data;
    struct node *left;
    struct node *right;
};

( struct node *) createNode(int num)
{
    struct node *newNode;
    newNode = (struct node *) malloc(sizeof(struct node));
    newNode->data = num;
    newNode->left = NULL;
    newNode->right = NULL;
    return newNode;
}

Answer 1

change

( struct node *) createNode(int num)

to

struct node * createNode(int num)

Remember, you're specifying the return type . You're not typecast ing.

That said,

1. Please see why not to cast the return value of malloc() and family in C .
2. Always check for the return value of malloc() for success before using the returned pointer.

Answer 2

Function: ( struct node *) createNode(int num) is invalid syntax. A pointer to a struct node* is the return type of the function. It seems you may have thought you must cast it to the struct type. That is not necessary. Furthermore, there is no need to cast malloc in C. Change it to this.

struct node* createNode(int num)
{
   /* ... */
}

Not necessary, but, to save on typing struct each time, better yet, you can define a new type with typedef .

typedef struct node Node;

struct node{
    int data;
    Node *left;
    Node *right;
};

Answer 3

While returning the structure you don't need to give the parenthesis for that. So simply You give the

  struct node * createNode(int num){
  ...
  }

Placing the brackets that is not correct.

Answer 4

You dont have to use parenthesis in return type of function definition. I think you are confused with the function definition here are few links:-

http://www.tutorialspoint.com/cprogramming/c_functions.htm

For function returning pointers

http://www.tutorialspoint.com/cprogramming/c_return_pointer_from_functions.htm

Type casting can only be use to a constant, variable, function calls (if returning something).

Explicit type conversion rule:-

http://www.tutorialspoint.com/cprogramming/c_type_casting.htm