Arrow operator (->) usage in C

Question

I am reading a book called \"Teach Yourself C in 21 Days\" (I have already learned Java and C# so I am moving at a much faster pace). I was reading the chapter on pointers a

Answer 1

#include<stdio.h>
struct examp{
int number;
};
struct examp a,*b=&a;`enter code here`
main()
{
a.number=5;
/* a.number,b->number,(*b).number produces same output. b->number is mostly used in linked list*/
   printf("%d \n %d \n %d",a.number,b->number,(*b).number);
}

output is 5 5 5

Answer 2

I had to make a small change to Jack's program to get it to run. After declaring the struct pointer pvar, point it to the address of var. I found this solution on page 242 of Stephen Kochan's Programming in C.

#include <stdio.h>

int main()
{
  struct foo
  {
    int x;
    float y;
  };

  struct foo var;
  struct foo* pvar;
  pvar = &var;

  var.x = 5;
  (&var)->y = 14.3;
  printf("%i - %.02f\n", var.x, (&var)->y);
  pvar->x = 6;
  pvar->y = 22.4;
  printf("%i - %.02f\n", pvar->x, pvar->y);
  return 0;
}

Run this in vim with the following command:

:!gcc -o var var.c && ./var

Will output:

5 - 14.30
6 - 22.40

Answer 3

Yes, that's it.

It's just the dot version when you want to access elements of a struct/class that is a pointer instead of a reference.

struct foo
{
  int x;
  float y;
};

struct foo var;
struct foo* pvar;
pvar = malloc(sizeof(pvar));

var.x = 5;
(&var)->y = 14.3;
pvar->y = 22.4;
(*pvar).x = 6;

That's it!

Answer 4

foo->bar is equivalent to (*foo).bar, i.e. it gets the member called bar from the struct that foo points to.

Answer 5

#include<stdio.h>

int main()
{
    struct foo
    {
        int x;
        float y;
    } var1;
    struct foo var;
    struct foo* pvar;

    pvar = &var1;
    /* if pvar = &var; it directly 
       takes values stored in var, and if give  
       new > values like pvar->x = 6; pvar->y = 22.4; 
       it modifies the values of var  
       object..so better to give new reference. */
    var.x = 5;
    (&var)->y = 14.3;
    printf("%i - %.02f\n", var.x, (&var)->y);

    pvar->x = 6;
    pvar->y = 22.4;
    printf("%i - %.02f\n", pvar->x, pvar->y);

    return 0;
}

Answer 6

Dot is a dereference operator and used to connect the structure variable for a particular record of structure. Eg :

struct student
    {
      int s.no;
      Char name [];
      int age;
    } s1,s2;

main()
    {
      s1.name;
      s2.name;
    }

In such way we can use a dot operator to access the structure variable