Dynamic Memory allocation

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Dynamic Memory allocation

 
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  #1
Oct 2nd, 2009
01 Why i am not able to do this
C++ Syntax (Toggle Plain Text) 
  1. int* px;
  2. px = new int[2][2];
other the px = new int[2*2]; is there any other method

02 Why i am not able do access through pointer dx by dx[1][2] other than by using dx[1*7+2]
cpp Syntax (Toggle Plain Text) 
  1. static float mat[5][7] =
  2. 	{
  3. 	        -5, -4,  0,  0,  0,  0,  0,
  4. 		 6,  4,  1,  0,  0,  0, 24,
  5. 		 1,  2,  0,  1,  0,  0,  6,
  6. 		-1,  1,  0,  0,  1,  0,  1,
  7. 		 0,  1,  0,  0,  0,  1,  2
  8. 	};
  9. 	float *dx=&sim_max[0][0];
  10. 	cout<<dx[1][0];

03 why i am not able to directly initialize array of new dynamically alloc. mem to
C++ Syntax (Toggle Plain Text) 
  1. float *dx= new float[5*7]
  2. 	(
  3. 		-5, -4,  0,  0,  0,  0,  0,
  4. 		 6,  4,  1,  0,  0,  0, 24,
  5. 		 1,  2,  0,  1,  0,  0,  6,
  6. 		-1,  1,  0,  0,  1,  0,  1,
  7. 		 0,  1,  0,  0,  0,  1,  2
  8. 	);
Last edited by Rhohitman; Oct 2nd, 2009 at 3:38 pm.
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Re: Dynamic Memory allocation

 
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  #2
Oct 2nd, 2009
Well Dynamic 2D arrays take a little more complexity.This is mainly because when you declare something like this

C++ Syntax (Toggle Plain Text) 
  1. int *p;
  2. p= new int [2][2];
What you are trying to do is assigning a pointer array to a pointer itself.
THe new int [2][2] converts itself into a pointer array in this case it is something like int * [2] So In order to Dynamically Create a 2D array you will need to do something like this.

C++ Syntax (Toggle Plain Text) 
  1.  int *p,**q;
  2.    q=new int* [2];
  3.    q[0]=new int [2];
  4.    q[1]=new int [2];
  5.    delete []q[0];
  6.    delete [] q[1];
  7.    delete [] q;
So now you have a 2d array whose elements you can access.
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Re: Dynamic Memory allocation

 
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  #3
Oct 2nd, 2009
I've always found it simpler to allocate a one-dimensional array, and then calculating the row and column manually, it's an easy approach, and it works.
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Re: Dynamic Memory allocation

 
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  #4
Oct 2nd, 2009
Thanx Sky Diploma
here things got too much complicated
C++ Syntax (Toggle Plain Text) 
  1. Temp2=T1->dx[i*T1->n+T1->n-1] / T1->dx[i*T1->n+pivot_j];

i guess i have to use the loop for assigning the value inside it..
Last edited by Rhohitman; Oct 2nd, 2009 at 4:30 pm.
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Re: Dynamic Memory allocation

 
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  #5
Oct 2nd, 2009
Yes, Btw, Dont forget deleting each one of the dynamic pointers . Before you delete the pointer to pointer.
And yea, Loops could assign values.
Another solution would be to use vectors.
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