?
Solved

dynamic array declration

Posted on 2004-03-26
10
Medium Priority
?
443 Views
Last Modified: 2013-12-14
i want to know if it is possible to declare an array of the type

int array[ length ]; where length is a variable.

i don't want to use malloc and calloc as they complicate the program.

i get an error message "Constant Expression Required"

is there any way of making the length constant so that the above statement is valid ??

i need this for a class called Timer

i want to declare it as

Timer T[5][length];
Where length is  a variable.

is it possible ??
( without using malloc and calloc as far as possible )

0
Comment
Question by:radarsh
[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
10 Comments
 
LVL 86

Accepted Solution

by:
jkr earned 256 total points
ID: 10690847
>>i want to know if it is possible to declare an array of the type
>>int array[ length ]; where length is a variable.

Not if you are using VC++. You might want to use std::vector, e.g.

#include <vector>


std::vector<int> array(lenght);
0
 
LVL 44

Expert Comment

by:Karl Heinz Kremer
ID: 10690855
Your compiler tells you that it's not possible...

You are asking this in the C++ area, so why not just use a C++ feature? The STL vector is like an array, but it allocates it's memory dynamically in the background. This means that you don't have to take care of this yourself.

#include <vector>
using namespace std;

vector<Timer> T;

... then just use T like an array:
T[0] = ...
T[1] = ...
T[2] = ...

0
 
LVL 1

Assisted Solution

by:GJanusz
GJanusz earned 248 total points
ID: 10691205
I, too, would use vector.  How you use it is another matter, of course.  There are probably many ways.  Personally, working with a variable array of a constant array of class instances confuses me sometimes (hopefully not for the duration of this post).

I might consider coding it this way:

typedef struct {
      Timer      y[5];
} Timer5;
0
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.

 
LVL 1

Expert Comment

by:GJanusz
ID: 10691232
And the rest of my post ... (note that the typedef struct could be a class instead if you like)

vector<Timer5> T;
T.resize(nLength);

Then you can reference Timer instances with references that look like:
T[29].y[4]

In real life, I tend to run into situations more where I want to have a vector of vectors, in which case, I make my life simpler by defining something like this:

typedef vector<something> T_vSomething;

Then I can allocate a vector of a vector of somethings with:
vector<T_vSomething> myvv;
0
 
LVL 39

Assisted Solution

by:itsmeandnobodyelse
itsmeandnobodyelse earned 248 total points
ID: 10692553
The C++ equivalent of malloc is the new operator. You can do something like this:

class T
{
private:
    char* ps;
    int  i;
public:
    T() : ps(new char[10]), i(0) {}
    ~T() { delete [] ps; }
};

int main(int nArgs, char* szArgs[])
{

    typedef T T5[5];
    long len = 2;
    T5* pT5 = new T5[len];
   
    ...
    delete [] pT5;

    return 0;
}

Then you can have two dimensions - the first must be constant.

A dynamic container like vector is better, but vector<T> is an one-dimensional array.

Regards, Alex

0
 

Expert Comment

by:fsugolf06
ID: 10693172
heres a pretty simple solution here:

//first declare a pointer

int * array;

//then dynamically allocate the array like this:

array = new int[10][someVariable];

that should work
0
 
LVL 30

Assisted Solution

by:Axter
Axter earned 248 total points
ID: 10693542
>>array = new int[10][someVariable];

That works, but it leaves a potential for memory leaks just like malloc.

Here's another method:
http://axter.com/code/dynamic_2d_array.h

With the simple class in the above link, you can easily declare a 2-D array like this:

dynamic_2d_array<Timer> T[5][length];

For more information, and to see other methods for dynamically creating a 2D array, see the following link:
http://www.axter.com/faq/topic.asp?TOPIC_ID=60&FORUM_ID=4&CAT_ID=9
0

Featured Post

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!

Question has a verified solution.

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

Programmer's Notepad is, one of the best free text editing tools available, simply because the developers appear to have second-guessed every weird problem or issue a programmer is likely to run into. One of these problems is selecting and deleti…
Jaspersoft Studio is a plugin for Eclipse that lets you create reports from a datasource.  In this article, we'll go over creating a report from a default template and setting up a datasource that connects to your database.
The goal of the video will be to teach the user the difference and consequence of passing data by value vs passing data by reference in C++. An example of passing data by value as well as an example of passing data by reference will be be given. Bot…
The viewer will be introduced to the technique of using vectors in C++. The video will cover how to define a vector, store values in the vector and retrieve data from the values stored in the vector.
Suggested Courses

650 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