C help please

[guest]

Hello... could someone explain to me how to point to a variable within a struct?

ie

typedef struct
{
int x;
int y;
} my_struct

my_struct mem;


int *ptr;

(how would I piont this pointer to x or y?

ptr = &(mem.x) ??????????

thanks for any help with C

[dyeatman]

This is not a C Beginner training forum. However, you can find good information on struct by simply using Google. Here is a good link I found on the first try:

http://www.iota-six.co.uk/c/h2_introduction_to_struct.asp

This site also has excellent info on pointers and the entire C language here:

http://www.iota-six.co.uk/c/default.asp

Also search this user group for the word struct and you will find lots of examples.

The book C Programming Language by Kernighan, Ritchie is an excellent reference and you should get it as soon as possible.

Amazon.com has a used copy for $19 here:
http://www.amazon.com/exec/obidos/search-handle-form/002-9403352-2272044

[Guest]

Thanks for the reply - I've used pointers many times over etc... however I'm having trouble making a pointer to a member of a struct. I've read many references and I can't seem to figure this one out.

Since I'm a CCS customer, I thought I'd post my question here in case anybody could provide help.

Thanks.

[bdavis]

I would suggest buying the K&R book for an ANSI 'C' reference, and another book for learning 'C'. You may also want to consider using a different compiler for learning C because the CCS does not have as good of error or warning messages as a large C compiler would. You could get the Borland , or Watcom C for free I think, or a used copy of Visual C++.

[dyeatman]

I searched this user group with the specifiers "struct AND pointer" and found the answer to to your question.

Please see this link:

http://www.ccsinfo.com/forum/viewtopic.php?t=19428

[valemike]

example:

struct mike_s
{
int x;
int y;
};

struct mike_s michael; // michael
struct mike_s *michael_ptr; // uninitialized pointer to mike_s

....
michael_ptr = michael; // this initialized the pointer to point to something meaningful

//now you can do stuff to the structure...
michael_ptr->x = 20;

Similiarly, you can do the following:
michael.x = 20;

So, if you work directly on the struct, you use a ".", but if you use a pointer to the structure, then you use a "->"

[guest]

Again, thanks for replies.

Maybe I should explain more of what I'm trying since received answers aren't what I'm looking for ->

typedef struct{
int x;
int y;
int *ptr;
}mystruct

mystruct xyz;

void main()
{

xyz.x = 2;
xyz.y = 5;

/* now I'd like to point ptr at either x or y; */

xyz.ptr = &(xyz.x);


Is this not valid in CCS? My GCC compiler does not complain and printing out results shows that this is fine, but my CCS gives me a warning (I can't recall what that warning exactly says, since I am not at home at work at the moment).

[Mark]

This works just fine. No complaints except for the endless while(1)