Solved

Accessing structures in functions in C++

Posted on 2000-03-20
6
322 Views
Last Modified: 2010-04-02
I have some functions that take in structures, amongst other things.
eg.
int winapi rectangle(SIZES *pInfo);

...where SIZES is a structure. How can I assign values to the variables of the Structure SIZES? I'v tried creating an object of type SIZES and assigning values using the (.)
 SIZES MySizes;  //create a Sizes object
*mySizesPtr=&mySizes, //pointer       &mySizesRef=mySizes;  //reference

mySizes.version = 0x03000000;

But I'm not sure that this is assigning the values to the right place.
Pls can i have a simple example of how to do this correctly. Pls help!

0
Comment
Question by:nicolac
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
6 Comments
 
LVL 2

Accepted Solution

by:
xLs earned 50 total points
ID: 2638436
example
int winapi rectangle(SIZES* pInfo)
{
   pInfo->version = 0x0300000;
 SIZES s = *pInfo; // example of copy
}

in method:
{

 SIZES mySize;
 rectangle(&mySize); // '&' since rectangle needs a pointer of SIZES.
 printf("%d", mySize.version);
}



e.g if its a pointer to an instance of SIZES you use -> to assing or extract value or '*' as prefix.

if it is not a pointer you use '.'.


what you did
SIZES MySizes; //MySizes is not a pointer

*mySizesPtr=&mySizes;
// &mySize is the pointer of mySize
// *mySize is invalid because mySize is not a pointer

think of it this way:

*mySize lets you access whatever the pointer holds (its the mySizes instance).

&mySize gives you the pointer of the instance mySize


this is quite anoying to explain but ehm. comment if you need better explaination :)
0
 
LVL 10

Expert Comment

by:RONSLOW
ID: 2638623
Two ways...

int winapi rectangle(SIZES *pInfo) {
  pInfo->xxxx = yyy;
}

or

int winapi rectangle(SIZES *pInfo) {
  SIZES& sizes = *pInfo;
  sizes.xxxx = yyyy;
}

The first accesses directly from the pointer with ->

The second uses a reference, and you can then use '.'

Both of the above will change the thing pointed to by pInfo.

If you take a COPY of the thing pointed to by pInfo and change that, then the original is unchanged.



0
 

Expert Comment

by:kaushikg
ID: 2639673
Both person has replied correctly but RONSLOW's explanation is easy to understand.
0
Independent Software Vendors: We Want Your Opinion

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

 
LVL 13

Expert Comment

by:Kelvin_King
ID: 2639845
what does the -> mean ?
0
 
LVL 10

Expert Comment

by:RONSLOW
ID: 2639925
p->x is just shorthand for

(*p).x

ie. it dereferences the pointer to a struct and then gets the member of the struct.

or simpler...

ie. it does a '.' on the object pointed to by p

pointers are a tricky C concept for many to grasp.

even trickier for some is C++ references, which is what I used in the other example.

0
 

Author Comment

by:nicolac
ID: 2655601
Thanks, I understand now :)
0

Featured Post

Technology Partners: We Want Your Opinion!

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

When writing generic code, using template meta-programming techniques, it is sometimes useful to know if a type is convertible to another type. A good example of when this might be is if you are writing diagnostic instrumentation for code to generat…
Article by: SunnyDark
This article's goal is to present you with an easy to use XML wrapper for C++ and also present some interesting techniques that you might use with MS C++. The reason I built this class is to ease the pain of using XML files with C++, since there is…
The goal of the video will be to teach the user the concept of local variables and scope. An example of a locally defined variable will be given as well as an explanation of what scope is in C++. The local variable and concept of scope will be relat…
The viewer will learn how to use the return statement in functions in C++. The video will also teach the user how to pass data to a function and have the function return data back for further processing.

705 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question