Thread: Typedef

just a question

Code:

struct stackNode
{
int data;
struct stackNode *nxt
}
typedef struct stackNode StackNode;
typedef StackNode *StackNodePtr;

is

Code:

typedef struct stackNode StackNode;

the same as

Code:

struct stackNode StackNode

and is

Code:

typedef StackNode *StackNodePtr;

the same as

Code:

struct stackNode *StackNodePtr

can anyone transcribe ? this or ? correct me? I am kinda getting confused

Don't use devil-words like "instantiate" in C forum.

Originally Posted by nonoob

Don't use devil-words like "instantiate" in C forum.

Oh my ....

Originally Posted by nonoob

Don't use devil-words like "instantiate" in C forum.

I object; CommonTater showed some class when he used the word "instantiate".

Tim S.

Warning: Incorrigible punster don't encourage.

It's a struct without method!

Originally Posted by Bayint Naung

It's a struct without method!

Yet strangely, it does exist.

I think Tater covered it pretty well, but due to your confusing code, he made a few small boo boos:

Originally Posted by CommonTater

Not exactly....
struct stackNode StackNode defines one structure that can be used in your program.
But typedef struct stackNode Stacknode defines a new type that can be used to instantiate structs as in...

Code:

stackNode Fred;

This should actually be StackNode Fred. stackNode is the struct name, which would require the word struct in front of it before the variable definition. StackNode, with the capital S is shorthand for struct stackNode.

Code:

and is 

	
Code:
	
typedef StackNode *StackNodePtr;
 the same as 

	
Code:
	
struct stackNode *StackNodePtr

It's the same concept as above except this time you're defining pointers to stackNodes.

One is a type definition and the other is a variable definition. The former defines a new type, StackNodePtr, that is a pointer to type StackNode. The latter defines a variable named StackNodePtr that is of type pointer to struct stackNode.

Originally Posted by kyel_dai92

can anyone transcribe ? this or ? correct me? I am kinda getting confused

So am I. A couple rules I like to follow for working with structs and typedefs, and code in general, are this:

First off, don't make two names (type names, variable names, etc) differ only by case. That is, stackNode and StackNode are very confusing and lead to all kinds of problems, from a simple miss of the shift key. I often use a simple suffix:

Code:

typedef struct stack_s      stack_t; // define stack_t type as shorthand for "struct stack_s"
struct stack_s {
    int data;
    stack_t *next;  // pointer to another struct, just like this one
};

stack_t *top = NULL;  // pointer to the top of the stack

I use the _s for structs and _t for typedef'ed types. I also like putting the typedef above the struct definition, since it allows me to use the shorthand name inside the struct.

Second, don't mask indirection/pointerness in a typedef. It makes it difficult to track down problems and really know what your code is doing with memory. Avoid anything like:

Code:

typedef StackNode *StackNodePtr;  // evil, don't use a * in a typedef

OMG I am confuse , soo they are not the same? well the they have the same concept but , anyways I'll put my whole coede here I guess? just to make it more understandable


This is the original code

Code:

#include<stdio.h>
#include<stdlib.h>

struct stackNode
{
       int data;
       struct stackNode *nxt;
       };

typedef struct stackNode StackNode;
typedef StackNode *StackNodePtr;




void instructions()
{
     printf("        Please Select a Number to do the following\n\n");
     printf("              [1]Push a value\n");
     printf("              [2]Pop a value\n");
     printf("              [2]Peek a node\n");
     printf("              [3]Display\n");
     printf("              [4]Exit\n               ");
     }
     
     int main ()
     {
         int value; 
         int choice;
         Stack = NULL;
         
         instructions();
     
     do
     {
       scanf("%d",&choice);
         system("cls");
         
         
         if(choice == 1)
             {
                 
                                       }
                     
              if(choice == 2)
              {
                        printf(" "); 
                        }       
              if(choice == 3)
              {
                        
                        printf(" ");
                        }
                if(choice == 4 )
                {
                          
                          printf("bye!");
                          return 0;
                          }      
                          
                          
               
         }while(choice !=4);
             
         getch();
         }

but I changed it to

Code:

#include<stdio.h>
#include<stdlib.h>

struct stackNode
{
       int data;
       struct stackNode *nxt;
       };

struct stackNode STACK;
struct stackNode *Stack;



void instructions()
{
     printf("        Please Select a Number to do the following\n\n");
     printf("              [1]Push a value\n");
     printf("              [2]Pop a value\n");
     printf("              [2]Peek a node\n");
     printf("              [3]Display\n");
     printf("              [4]Exit\n               ");
     }
     
     int main ()
     {
         int value; 
         int choice;
         Stack = NULL;
         
         instructions();
     
     do
     {
       scanf("%d",&choice);
         system("cls");
         
         
         if(choice == 1)
             {
                 
                                       }
                     
              if(choice == 2)
              {
                        printf(" "); 
                        }       
              if(choice == 3)
              {
                        
                        printf(" ");
                        }
                if(choice == 4 )
                {
                          
                          printf("bye!");
                          return 0;
                          }      
                          
                          
               
         }while(choice !=4);
             
         getch();
         }

are they still the same or different?

No, they are not the same.

In your first piece of code, you use typedef. Using typedef does not actually create a variable. It is just a way to make a synonym for another type.
typedef struct stackNode StackNode;
typedef is just a keyword, that tells the compiler to make a synonym
struct stackNode is the original type
StackNode is the name of the new synonym. Anywhere you use struct stackNode, you can now use .StackNode

In your second piece of code, you don't use typedef. That means you define variables. You define a variable with type variable_name
struct stackNode STACK;
struct stackNode *Stack;

Originally Posted by Babkockdood

Code:

struct stackNode *StackNodePtr

Not sure about this last one. I'm not too familiar with typedef, I've seen it in header files, mostly paired with structures. I'm sure someone else can provide a better answer.

That's creating a (uninitialized) pointer to the struct.

and what's the solution for typedef StackNode *StackNodeptr?

Originally Posted by kyel_dai92

and what's the solution for typedef StackNode *StackNodeptr?

Look up the typedef keyword in your C book....

Really, it's not a difficult concept.