Solved

Dynamic 2-dimensional array

Posted on 2003-10-30
7
488 Views
Last Modified: 2010-04-01
I am trying to declare a 2-dimensional array at runtime.  I can declare a 1 dimensional array as follows:

unsigned int * MyVariable;
MyVariable = new unsigned int[12];

However, the following does not work.

unsigned int * MyVariable;
MyVariable = new unsigned int[12][8];

I am using Microsoft Visual C++ 6.0 if it is of any help.

If it is an overloading solution some code would be useful.

Many thanks in advance.
0
Comment
Question by:reidy_boy
7 Comments
 
LVL 14

Accepted Solution

by:
Farzad Akbarnejad earned 50 total points
ID: 9652130
Hi,


      unsigned int * MyVariable1;
      MyVariable1 = new unsigned int[12];

      // ------------------------------------------

      unsigned int ** MyVariable2;
      MyVariable2 = new unsigned int * [8];
      for (int i = 0; i < 11; i++)
            MyVariable2[i] = new unsigned int [8];


-FA
0
 
LVL 14

Expert Comment

by:Farzad Akbarnejad
ID: 9652143
Hello,
Sorry change

MyVariable2 = new unsigned int * [8];

with

MyVariable2 = new unsigned int * [12];

-FA
0
 
LVL 10

Expert Comment

by:Sys_Prog
ID: 9652262
int **a ;

a = new int * [10] ;
for ( int i = 0 ; i < 10 ; i ++ )
  a [i] = new int [20] ;

This would get a array same as
a[10][20]

0
Networking for the Cloud Era

Join Microsoft and Riverbed for a discussion and demonstration of enhancements to SteelConnect:
-One-click orchestration and cloud connectivity in Azure environments
-Tight integration of SD-WAN and WAN optimization capabilities
-Scalability and resiliency equal to a data center

 
LVL 30

Expert Comment

by:Axter
ID: 9654864
You can use the following class to dynamically create a 2 dimensional array:

template < class T, int ROW_T = 0, int COL_T = 0 >
class dynamic_2d_array
{
public:
    dynamic_2d_array(int row, int col):m_row(row),m_col(col), m_data((row!=0&&col!=0)?new T[row*col]:NULL){}
    dynamic_2d_array():m_row(ROW_T),m_col(COL_T), m_data(new T[ROW_T*COL_T])
      {if (!COL_T || !ROW_T) {int x[ROW_T] = {{ROW_T}};int y[COL_T] = {{x[0]}};}}
    ~dynamic_2d_array(){if(m_data) delete []m_data;}
    T* operator[](int i) {return (m_data + (m_col*i));}
    T const*const operator[](int i) const {return (m_data + (m_col*i));}
private:
    const int m_row;
    const int m_col;
    T* m_data;
};
0
 
LVL 30

Expert Comment

by:Axter
ID: 9654882
Example usuage:
            dynamic_2d_array < int > dyn_2dArray(Q_Col, Q_Row);
            StartTime = GetTickCount();
            for (int t = 0;t < QtyTestItera;++t)
            for(int i0 = 0;i0 < Q_Col;++i0)
            {
                  for(int i1 = 0;i1 < Q_Row;++i1)
                  {
                        dyn_2dArray[i0][i1] = i0 + i1;
                  }
            }

Check out following link for more details on other methods for creating a dynamic two dimensional array:
http://www.axter.com/faq/topic.asp?TOPIC_ID=60&FORUM_ID=4&CAT_ID=9
0
 
LVL 15

Expert Comment

by:efn
ID: 9655746
When you allocate an array of objects of some type T, you get a pointer to T.  With

new unsigned int[12][8]

you are allocating an array of 8-integer arrays, so you get a pointer to an 8-integer array, which is not the same as a pointer to an integer.  So all you have to do is declare MyVariable like this:

unsigned int (* MyVariable)[8];

The parentheses are necessary to get a pointer to an array, rather than an array of pointers.

This only works if the 8 is a constant, as shown in your question.  If it's a variable, see the other answers.

--efn
0
 
LVL 1

Author Comment

by:reidy_boy
ID: 9656684
Thank you experts for your comments.  All are good answers, but I have given the points to FarzadA because it was the simplest.  Sys_Prog, your answer was along the same lines as FarzadA but he got there first!!!
0

Featured Post

Free Tool: IP Lookup

Get more info about an IP address or domain name, such as organization, abuse contacts and geolocation.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

Question has a verified solution.

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

Suggested Solutions

Title # Comments Views Activity
basic hardware to learn oop advanced design patterns 3 101
Add values of each row in an array 3 64
DCT of  2D array using fftw in c++ 9 68
C++ help/ Toy problem 19 30
Errors will happen. It is a fact of life for the programmer. How and when errors are detected have a great impact on quality and cost of a product. It is better to detect errors at compile time, when possible and practical. Errors that make their wa…
  Included as part of the C++ Standard Template Library (STL) is a collection of generic containers. Each of these containers serves a different purpose and has different pros and cons. It is often difficult to decide which container to use and …
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 additional member functions of the vector class. Specifically, the capacity and swap member functions will be introduced.

839 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