What is the difference between these three statements?

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Considering my struct:

typedef struct node *Node; 
struct node{     
  Item value;     
  struct node *next; 
};

What is the difference between these three statements?

1. Node n = malloc(sizeof(struct node));
2. Node n = malloc(sizeof(Node));
3. struct node *n = malloc(sizeof(struct node));

What I have tried:

I noticed that the second one create problems with the input. Is there actually a difference between these?

Posted 9-Jul-21 6:10am

Gianpiero Piscitella

Updated 9-Jul-21 6:26am

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k5054 · Answer 1 · 2021-07-09T06:26:00

Statements 1. and 3. are equivalent, and allocate a block of memory the size of struct node

Statement 2, on the other hand, allocates a block of memory the size of Node. Now, Node has been typedef-ed to struct node *, so statement 2 could be rewritten as

C

Node n = malloc(sizeof(struct node *))

This allocates a block for a pointer, not the size of the thing the pointer points to. For most systems in use today, that will either be 4 or 8 bytes, depending on whether the the system uses 32 or 64 bits natively.