Still celebrating National IT Professionals Day with 3 months of free Premium Membership. Use Code ITDAY17

x
?
Solved

struct within a struct?

Posted on 1998-11-02
4
Medium Priority
?
387 Views
Last Modified: 2010-04-02
Is it valid to create a struct within a struct as below and then access the data directly. See example of implementation below definition.

/************************************************************************************
// DRIVER_INFO
// -----------
//
// Structure to encapsulate information required just by the driver and
// the scheduler.
//
 ************************************************************************************/
typedef struct driver_info
{
      struct driver
      {
            int buffer_id;

            bool process_image;
            UINT height;
            UINT width;
            PIXEL_DATA_FORMAT image_format;
            VIDEO_FORMAT video_format;
      } driver;

      struct scheduler
      {
            std::list<information_buffer*> results_list;
            std::list<information_buffer*> free_buffer_pool;
      } scheduler;

} driver_info;

main()
{
 driver_info data;
 data.driver.height = 100;
 ASSERT(data.driver.height == 100);
}

This compiles but when I attempt to debug I can not see the variables within the inner struct. I can set them and read them in code. My alternative is to convert the struct to a typedef and instantiate an instance of it:

typedef struct driver_struct
{
 UINT height;

 etx, etc
} driver_struct;

driver_struct driver;

This also works and allows access to the inner struct as well as displaying the instantiated variables in the debugger.

I am using VC6.0.
0
Comment
Question by:sdj
[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
  • 3
4 Comments
 
LVL 22

Accepted Solution

by:
nietod earned 400 total points
ID: 1176810
>>Is it valid to create a struct within a struct as below and then access the data directly
Yes it is valid.  If it weren't valid it wouldn't compile.

continues
0
 
LVL 22

Expert Comment

by:nietod
ID: 1176811
I would suggest the following changes, they should allow you to see the members inside the structure.  

The "typedef stuct" syntax is not needed in C++ (like it was in C).  Not is the "struct" before you declare an instance of a structure.  

Don't create anonymous structure types.  That is structure that have a single instance and not specified type name.

This cleans up the stucture to.

struct driver_info
{
   struct driverType // Now it isn't anonymous.
   {
      int buffer_id;

      bool process_image;
      UINT height;
      UINT width;
      PIXEL_DATA_FORMAT image_format;
     VIDEO_FORMAT video_format;
   }
  driverType driver;  // Declare driver using the driverType structure  type/

   struct schedulerType // again not annonymous.
   {
      std::list<information_buffer*> results_list;
      std::list<information_buffer*> free_buffer_pool;
   }
   schedulerType scheduler;  // Again used declared type.

};  // don't need type here.

I think this will clean up your problems.  Let me know if you have questions.
0
 

Author Comment

by:sdj
ID: 1176812
I have just tried doing the following:

struct driver_info
{
   struct driverType // Now it isn't anonymous.
   {
      int buffer_id;

      bool process_image;
      UINT height;
      UINT width;
      PIXEL_DATA_FORMAT image_format;
     VIDEO_FORMAT video_format;
   } driver;  // Declare driver using the driverType structure  type/

This also works, I assume it is the same thing? I.E. define the struct driverType and declare one called driver, as this works in the debugger. It appears the debugger does not like it if the declared type has the same name as the struct.
0
 
LVL 22

Expert Comment

by:nietod
ID: 1176813
>> It appears the debugger does not like it if
>> the declared type has the same name as the struct
That is probably the real heart of the problem.  In C that was not a problem since the stucture name was always preceeded with a "struct" keyword.  C++ did away with that and it can lead to some ambiguity now if the structure type name and a object name are the same.
0

Featured Post

What does it mean to be "Always On"?

Is your cloud always on? With an Always On cloud you won't have to worry about downtime for maintenance or software application code updates, ensuring that your bottom line isn't affected.

Question has a verified solution.

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

In days of old, returning something by value from a function in C++ was necessarily avoided because it would, invariably, involve one or even two copies of the object being created and potentially costly calls to a copy-constructor and destructor. A…
IntroductionThis article is the second in a three part article series on the Visual Studio 2008 Debugger.  It provides tips in setting and using breakpoints. If not familiar with this debugger, you can find a basic introduction in the EE article loc…
The goal of the tutorial is to teach the user how to use functions in C++. The video will cover how to define functions, how to call functions and how to create functions prototypes. Microsoft Visual C++ 2010 Express will be used as a text editor an…
The viewer will learn how to user default arguments when defining functions. This method of defining functions will be contrasted with the non-default-argument of defining functions.

704 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