In the books I read that the syntax for malloc is malloc(sizeof(int)) but in one of doubly linked list program I see the following:
newnode=(struct node *)malloc(sizeof(struct node))
What is (struct node*) doing here? What is this entire code doing? btw, the code for the struct in the program is as below.
struct node
{
char line[80];
struct node *next,*prev;
};
struct node *start=NULL,*temp,*temp1,*temp2,*newnode;
Thank you
The code is dynamically creating a pointer to a single type of struct node. In most versions of C, the (struct node *) cast is not needed, and some argue that it shouldn't be used. If you remove the cast, it will be a void*, which can be used for any type.
Therefore:
newnode = (struct node*)malloc(sizeof(struct node));
is roughly equivalent to:
newnode = malloc(sizeof(struct node));
See: Specifically, what's dangerous about casting the result of malloc?
Note 1: If you are using Visual Studio to write your C code, it will give you red underlining if you don't cast the result of malloc. However, the code will still compile.
Note 2: Using malloc in C++ code requires you to cast the result as shown in your example.
int to struct node*. Effectively hiding the error. There should be no cast on that line. Secondly, the question is tagged with C, what C++ does has no bearing here. Thirdly, a bug in a compiler (or an IDE) is no reason to use bad code.You ran into a very bad code. C programmers never cast a result of malloc(). Not only it is not needed but can be harmful.
You should pass the number of bytes that you want malloc to allocate as argument. That is why in this code sample you use sizeof(struct node) telling C to allocate the number of bytes needed for a struct node variable. Casting the result like is shown in this code is bad idea by the way.
malloc returns a void pointer .
(struct node*) does a explicit conversion from void pointer to the target pointer type
"malloc" returns a void-pointer. (struct node *) is type-casting the result of malloc to a "node struct pointer", which is (undoubtibly) what "newnode" is.
