Thread: What does this symbol mean: ->

For C....

If you have a structure called mystruct with a member called var, you would access var with mystruct.var.

If you had a pointer to the structure, you would use mystruct->var

Buy a good book about C, for example "The C Programming Language" and learn some C, or read some reference.

klausi

Code:

struct FOO
{
    char *stuff = "floobie";
};

int main(void)
{
    struct FOO foo;
    struct FOO *pFoo;

    puts(foo.stuff); /*This will work, prints floobie*/
    puts(pFoo->stuff); /*okay here too, prints floobie*/

    puts(foo->stuff); 
    /*bzzzzt, wrong answer!
    **foo is a direct instance, not a pointer
    **-> is used to with a pointer to a struct
    */
    puts(pFoo.stuff);
    /*bzzzzt, also wrong!
    **pFoo is a pointer, treat it like one
    ** the . operator is used for a direct instance only
    */

    return EXIT_SUCCESS;
}

-Prelude

I'll make it even easier to understand:

some_struct->element is exactly the same as saying (*some_struct).element

But who wants to dereference a struct just to access its elements? It is a shortcut, like i++ or x |= 7.

a helpful aspect of this deferencing is that passing a pointer to a user defined conglomerate type as an argument to a function is a lot less expensive on the stack than passing the whole instance of the type...

x |= 7

It's like saying x = x | 7

the | symbol is the bitwsie OR.

It basically works like this...let's say you have two numbers, 2 and 1

0000000010 (binary 2)
0000000001 (binary 1)

well when you bitwise OR them, it comes out like this:

Code:

 0000000010
          | (OR)
 0000000001
---------------------
 0000000011

which is 3

see what it did? Every there was a 1 in a place that there wasn't one in the other number, it put a 1 there. You can basically think of it as adding or combining numbers in binary (but only think of it like that in binary terms, because 6 | 6 != 12, that 2 | 1 = 3 is just sorta a conincidence.