Typedef struct, pointers and passing pointers to a function

Question

Im kinda new to programming, so if someone could help me here id appreciate it!


typedef struct /*struct for circle creation*/
{
  int x_coord;
  int y_coord;
  int radius;
} circle, *circlepointer;

I need a pointer to a circle, and pass that pointer to a function that returns true if the circle radius is >0, and false otherwise. How do i pass my *circlepointer to a function and check this? I should be able to do something like circle.radius > 0, in the function

Hope you can help

Why bother with the *circlepointer typedef? All it does it add another type - and that type obfuscates the fact it's a pointer badly enough you have to put pointer in the type name. — Andrew Henle
– Andrew Henle, Commented Sep 30, 2019 at 13:17

Vlad from Moscow · Accepted Answer · 2019-09-30 14:08:25Z

3

The function can be declared like

int f( circlepointer c );

or

int f( const circle *c );

and called like

circle c = { /*...*/ };

f( &c );

Within the function you can access data members of the object like c->radius or ( *c ).radius.

Instead of the return type int you can also use the C type _Bool. Or you can include the header <stdbool.h> and write the return type as bool.

Pay attention to that these two function declarations

int f( const circlepointer c );

and

int f( const circle *c );

are not equivalent. In the first declaration the pointer itself is constant. In the second declaration the object pointed to by the pointer is constant.

edited Sep 30, 2019 at 14:08

answered Sep 30, 2019 at 13:03

Vlad from Moscow

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1 Comment

gustgr Over a year ago

Just to add to this answer, the radius member may be accessed in function f above through (*c).radius or c->radius.

Gianmarco · Accepted Answer · 2019-09-30 14:25:35Z

1

You can declare and define your function in this way

int func(circle * c) {
    return c->radius > 0;
}

Access a member via pointer can be done with -> operator or by dereferencing the pointer and then just use . operator to access its members

(*c).radius 
c->radius

then just call it in main

circle c = {your_x, your_y, your_radius};
func(&c);

answered Sep 30, 2019 at 14:25

Gianmarco

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