pointers and structures

[bukko]

Hi

My problem is this: If you declare a structure and then pass a pointer to it, to a function like this -

struct computer {
float cost;
int year;
char cpu_type[16];
};
typedef struct computer SC

void datain(SC *ptr_d); /*declare function*/

main()

SC model; /*struct variable declared*/

datain(&model) /*here is my problem*/

you have said in your function declaration you will pass a pointer of the SC type later on. However if you pass &model, thats not a pointer is it? Its just the address of the model struct variable.

Isnt a pointer supposed to be a memory address which contains a memory address. The content memory address pointing to the left side of your variable?

I am rather confused here can anyone help?

Thanks

Bukko

[Unregistered]

you need to declare a pointer to your structure and pass that

SC model;
SC *model_ptr;

model_ptr = &model;

datain(model_ptr);

[Salem]

> you have said in your function declaration you will pass a pointer of the SC type later on.
Thats correct.

> However if you pass &model, thats not a pointer is it?
Yes it is.

> Its just the address of the model struct variable.
Which is a pointer.

> Isnt a pointer supposed to be a memory address which contains a memory address.
A pointer is a variable which contains the address of some other variable.

SC model;
SC *ptr_to_model = &model;
datain ( &model );  // get the address of model, and pass that address to the function
datain ( ptr_to_model );  // read the contents of the variable, and pass that to the function (ie the value of &model)

Both mean and do exactly the same thing.

The advantage of the ptr_to_model method is that it allows you to dynamically create new SCs as and when you need them (pointing at an existing object doesn't add much).

[bukko]

Thanks guys that has made the whole thing much clearer.