C++ RSS C++ RSS

template array initialization

Please support our C++ advertiser: Intel Parallel Studio Home
Reply

•
•
Join Date: Jan 2005
Posts: 24
Reputation: crq is an unknown quantity at this point 
Solved Threads: 0
crq crq is offline Offline
Newbie Poster

template array initialization

 
0
  #1
Jan 27th, 2005
hey folks,

i have a template created that holds an array of type T elements. my problem is this ...

i am converting this code from a souped up Array class that takes ints as it's elements to this template Array<T> class that will hold T elements. in the original class, i knew that i was going to be dealing with ints as the elements. so i had a default constructor and a copy constructor that both called a private init method to initialize the array depending on what was passed in.

C++ Syntax (Toggle Plain Text) 
  1. void  IntArray::
  2. init ( const int *data, int sz)
  3. { 
  4.  
  5.         assert( (0 <= sz) && (sz <= MAXINT));
  6.  
  7.         d_num_elements = sz;
  8.         if ( 0 == d_num_elements ){          // if no elements in array
  9.                 d_array = NULL;                  // array points to NULL
  10.         }
  11.         else{
  12.                 d_array = new int [d_num_elements];
  13.                                                      // allocate memory
  14.                                                      // if new returns NULL then no
  15.                                                      // more available memory
  16.                 assert ( NULL != d_array );
  17.         }
  18.         for (int i=0; i < sz; i++ ){
  19.  
  20.                 if ( NULL == data ){
  21.                         self [i] = 0;
  22.                 }
  23.                 else{
  24.                         self[i] = data[i];
  25.                 }
  26.         }
  27. }

so how do i conver this to make it work for type T? i can't initialize the elements to 0 ...

thanks
crq
Reply With Quote Quick reply to this message  
•
•
Join Date: Sep 2004
Posts: 7,625
Reputation: Narue has a reputation beyond repute Narue has a reputation beyond repute Narue has a reputation beyond repute Narue has a reputation beyond repute Narue has a reputation beyond repute Narue has a reputation beyond repute Narue has a reputation beyond repute Narue has a reputation beyond repute Narue has a reputation beyond repute Narue has a reputation beyond repute Narue has a reputation beyond repute 
Solved Threads: 715
Team Colleague
Narue's Avatar
Narue Narue is offline Offline
Code Goddess

Re: template array initialization

 
0
  #2
Jan 28th, 2005
C++ Syntax (Toggle Plain Text) 
  1. void  IntArray::
  2. init ( const T *data, int sz)
  3. {
  4.         assert( (0 <= sz) && (sz <= MAXINT));
  5.  
  6.         d_num_elements = sz;
  7.         if ( 0 == d_num_elements ){          // if no elements in array
  8.                 d_array = NULL;                  // array points to NULL
  9.         }
  10.         else{
  11.                 d_array = new T [d_num_elements];
  12.         }
  13.         for (int i=0; i < sz; i++ ){
  14.                 if ( NULL == data ){
  15.                         self[i] = T();
  16.                 }
  17.                 else{
  18.                         self[i] = data[i];
  19.                 }
  20.         }
  21. }
>assert ( NULL != d_array );
This is a very bad idea for two reasons. First, assert is meant for debugging program errors. Memory allocation failing is not a program error, it's a runtime error that needs to be addressed other than abruptly terminating and giving the user a cryptic error message designed for programmers. Your first assert is good (though an exception would be better, see below), but your second is not. Also, classes should NEVER terminate the program. Throw an exception and have the calling application decide what to do. Finally, new doesn't return a null pointer by default anymore, it throws a bad_alloc exception. Once again, this is something that the calling application needs to handle, so you can just let the exception propagate.

I'll assume that your operator[] checks for d_array being null, otherwise the loop has a bug.
I'm here to prove you wrong.
Reply With Quote Quick reply to this message  
•
•
Join Date: Jan 2005
Posts: 24
Reputation: crq is an unknown quantity at this point 
Solved Threads: 0
crq crq is offline Offline
Newbie Poster

Re: template array initialization

 
0
  #3
Jan 28th, 2005
i have 2 constructors that use this function

C++ Syntax (Toggle Plain Text) 
  1. template<class T> 
  2. Array<T>::
  3. Array ( int sz )
  4. {
  5.  
  6.         assert ( 0 <= sz <= MAXINT );              
  7.         cout << "!!! IntArray default constructor called" <<endl;
  8.  
  9.         init ( NULL, sz );
  10. }
  11.  
  12. template<class T>
  13. Array<T>::
  14. Array ( const Array<T>& x )
  15. {
  16.         cout << "!!! IntArray copy constructor called" <<endl;
  17.  
  18.         init ( x.d_array, x.size() );
  19. }

since the default constructor assigns the number of elements, there would be a NULL declared for the array. i just don't know what to put in the init() method (for either of these) to make the initialization work for a template. i can't initialize everything to 0 becuase what i pass in MAY not be ints. i can't initialize all the T elements of the array to NULL can i?

thanks
crq


•
•
•
•
Originally Posted by Narue
C++ Syntax (Toggle Plain Text) 
  1. void  IntArray::
  2. init ( const T *data, int sz)
  3. {
  4.         assert( (0 <= sz) && (sz <= MAXINT));
  5.  
  6.         d_num_elements = sz;
  7.         if ( 0 == d_num_elements ){          // if no elements in array
  8.                 d_array = NULL;                  // array points to NULL
  9.         }
  10.         else{
  11.                 d_array = new T [d_num_elements];
  12.         }
  13.         for (int i=0; i < sz; i++ ){
  14.                 if ( NULL == data ){
  15.                         self[i] = T();
  16.                 }
  17.                 else{
  18.                         self[i] = data[i];
  19.                 }
  20.         }
  21. }
>assert ( NULL != d_array );
This is a very bad idea for two reasons. First, assert is meant for debugging program errors. Memory allocation failing is not a program error, it's a runtime error that needs to be addressed other than abruptly terminating and giving the user a cryptic error message designed for programmers. Your first assert is good (though an exception would be better, see below), but your second is not. Also, classes should NEVER terminate the program. Throw an exception and have the calling application decide what to do. Finally, new doesn't return a null pointer by default anymore, it throws a bad_alloc exception. Once again, this is something that the calling application needs to handle, so you can just let the exception propagate.

I'll assume that your operator[] checks for d_array being null, otherwise the loop has a bug.
Reply With Quote Quick reply to this message  
•
•
Join Date: Sep 2004
Posts: 7,625
Reputation: Narue has a reputation beyond repute Narue has a reputation beyond repute Narue has a reputation beyond repute Narue has a reputation beyond repute Narue has a reputation beyond repute Narue has a reputation beyond repute Narue has a reputation beyond repute Narue has a reputation beyond repute Narue has a reputation beyond repute Narue has a reputation beyond repute Narue has a reputation beyond repute 
Solved Threads: 715
Team Colleague
Narue's Avatar
Narue Narue is offline Offline
Code Goddess

Re: template array initialization

 
0
  #4
Jan 28th, 2005
>i can't initialize everything to 0 becuase what i pass in MAY not be ints.
I don't see what your problem is. If you read my answer you'll see that I used the default constructor for T (which works for built in types as well) as the replacement for 0. Did you try it? Or did you just assume that I haven't got a clue and proceed to give me irrelevant code snippets with the same question again?
I'm here to prove you wrong.
Reply With Quote Quick reply to this message  
•
•
Join Date: Jan 2005
Posts: 24
Reputation: crq is an unknown quantity at this point 
Solved Threads: 0
crq crq is offline Offline
Newbie Poster

Re: template array initialization

 
0
  #5
Jan 28th, 2005
•
•
•
•
Originally Posted by Narue
>i can't initialize everything to 0 becuase what i pass in MAY not be ints.
I don't see what your problem is. If you read my answer you'll see that I used the default constructor for T (which works for built in types as well) as the replacement for 0. Did you try it? Or did you just assume that I haven't got a clue and proceed to give me irrelevant code snippets with the same question again?
so sorry. i didn't realize that you had made changes to the code. the changes were minor fixes that make a world of difference. i didn't see them though. i thought you were quoting the code and had put it up to show me why the asserts did/didn't work. now i see that you took out the one that wasn't ok, and that you inserted the T. thanks for your help. i will try it now. didn't mean to imply that you "haven't got a clue". obviously, i am the one who hasn't got a clue. i won't bother you again.

thanks
crq
Reply With Quote Quick reply to this message  
•
•
Join Date: Sep 2004
Posts: 7,625
Reputation: Narue has a reputation beyond repute Narue has a reputation beyond repute Narue has a reputation beyond repute Narue has a reputation beyond repute Narue has a reputation beyond repute Narue has a reputation beyond repute Narue has a reputation beyond repute Narue has a reputation beyond repute Narue has a reputation beyond repute Narue has a reputation beyond repute Narue has a reputation beyond repute 
Solved Threads: 715
Team Colleague
Narue's Avatar
Narue Narue is offline Offline
Code Goddess

Re: template array initialization

 
0
  #6
Jan 28th, 2005
>i thought you were quoting the code and had put it up to show me why the asserts did/didn't work.
Fair enough. I can understand that mistake if you aren't familiar with my posting habits. Please ignore my previous comments.
I'm here to prove you wrong.
Reply With Quote Quick reply to this message  
Reply

Quick Reply to Thread
This thread is more than three months old.
Perhaps start a new thread instead?
•
•
•
•
•
•
•
•
Message:
•
•
•
•



Similar Threads
Other Threads in the C++ Forum
Thread Tools Search this Thread



api array based binary c++ c/c++ calculator char char* class classes code coding compile console conversion count database delete deploy desktop developer directshow dll download dynamic dynamiccharacterarray email encryption error file forms fstream function functions game givemetehcodez google graph gui homeworkhelp iamthwee ifstream input int integer java lib linkedlist linker linux list loop looping loops map math matrix memory multiple news number numbertoword output pointer problem program programming project python random read recursion recursive reference return rpg sorting string strings struct temperature template templates test text text-file tree unix url variable vector video visual visualstudio win32 windows winsock wordfrequency wxwidgets
About Us | Contact Us | Advertise | DaniWeb | Acceptable Use Policy | RSS Feed

©2003 - 2009 DaniWeb® LLC