Typedef 结构、指针和指向 function 的指针

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

Answer 1

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.

Answer 2

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);