dereferencing pointer to incomplete type

[santoshpandora]

Hi list !!!
I came across "dereferencing pointer to incomplete type" eror while compiling my code....

I have defined one structure as follows

typedef struct {
int a;
int b;
void ( * add ) ( int x , int y );
}add_t;

And in main program

int main () {

add_t *obj;
obj->a=12;
obj->b=34;
obj->add ( obj->a , obj->b ) ;

}

while compling it I got yhis error..

Can any one solve this?????

[Benny the Guard]

Three things I see.

1) You really want to be using a class here. Typedef struct is really old data types with C that just had data. If you're doing functions, use a class.

2) The method declaration is wrong. Do not surround the method name with parens.

3) You never defined what add does. So its incomplete.

With these mind try:

class add_t {
 public:
 
 int a;
 int b;
 int ( int x , int y ) { return (x+y); }
}

After you get that working you can add things like a constructor and move the data elements to the private class storage. If you want to do a typedef for some reason, you'll want to do:

typedef struct {
int a;
int b;
}add_t;

int
add (add_t *obj_ptr)
{
return (obj_ptr->a + obj_ptr->b);
}

[santoshpandora]

Hi Benny

Thanks for u r reply..
I am trying this in C not in C++.
Cause my module dosn't permit me to use C++.
One more add function simply adds two int. nothing else.

If possible show me the way in C to achive this.

Thanks
Santosh

[weaknessforcats]

This code:

int main () {

add_t *obj;
obj->a=12;
obj->b=34;
obj->add ( obj->a , obj->b ) ;

}

needs some work.

1) You declare an add_t pointer but you never put the address of an add_t object in the pointer. You can't use an uninitialized pointer.

2) add_t has a function pointer as a member but there is no function named add() whose address can be put in that pointer. Again, you need to initialize a pointer before using it.