Dynamic arrays

This is a discussion on Dynamic arrays within the C++ Programming forums, part of the General Programming Boards category; I have a piece of code which performs operations on a user defined amount of channels. I am trying to ...

  1. #1
    Registered User
    Join Date
    Sep 2007
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    4

    Dynamic arrays

    I have a piece of code which performs operations on a user defined amount of channels.
    I am trying to use an array to handle the channels (following Salem's advice) which works well when testing for an array of fixed length as below:

    Code:
    class class_name: 
    	.
    	.
    
    	protected:
    
    		virtual void function(int n, float *const *in, float *const *out);
    		float *Outchan[3];     // Declare Array for 4 Channels
    
    	.
    	.
    
    
    void class_name::function(int n, float *const *in, float *const *out)
    {
    	int i,nofout;
    	for (nofout=0; nofout<num_channels;nofout++)
    	{OutChan[nofout] = out[nofout];}   // Set number of outputs in signal vector
    
    	if (First==1)
    	{
    		ULStat = cbGetStatus (BoardNum, &Status, &CurCount, &CurIndex,AIFUNCTION);
    		for (nofout=0; nofout<num_channels;nofout++)
    				{OutChan[nofout] = 0;} // Give each channel a value in turn
    		}
    		
    		else First=0;
    	}
    
    	else
    	{
    		while (n>0)
    		{
    				for (nofout=0; nofout<num_channels;nofout++)  //adapt to varying channels
    				{
    					for (i=DuplicateSample;i>0;i--) //number of duplicate same sample
    					{
    						*OutChan[nofout]++ = ADData[OutCount];
    					}
    					*OutChan[nofout]++ = (ADData[OutCount++];
    					if (OutCount==Count) OutCount=0;
    				}
    				
    				n=n-(DuplicateSample+1);
    		}
    	}
    }
    However, I can't figure out how to adapt this to work with a dynamic array.
    I replaced
    Code:
    float *Outchan[3];
    with

    Code:
    float *OutChan;  // in class declaration
    . 
    OutChan= new float[num_channels];  // in the function
    But the compiler returns conversion errors.

    I suspect my phobia & lack of understanding of pointers are letting me down again!

    Could someone please explain how I would correctly use a dynamic array here?
    Thanks

  2. #2
    Kernel hacker
    Join Date
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    Location
    Farncombe, Surrey, England
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    What errors are you getting? Please copy and paste exact error messages, and mark the relevant lines with line-numbers.

    --
    Mats
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

  3. #3
    Registered User
    Join Date
    Jan 2005
    Posts
    7,317
    You are creating an array of float pointers, so OutChan should be a double pointer:
    Code:
    float **OutChan;  // in class declaration
    . 
    OutChan= new float*[num_channels];  // in the function
    Of course, there's little reason to use this kind of dynamic array, it will cause a lot more grief for you and your class when you can use vector instead:
    Code:
    std::vector<float *> OutChan;  // in class declaration
    . 
    class_name::class_name(int num_channels) : OutChan(num_channels)  // in constructor initialization list
    {
      // ... you could also resize it later with OutChan.resize(num_channels);
    }

  4. #4
    Registered User
    Join Date
    Sep 2007
    Posts
    4
    Daved your solution worked a treat.

    The tip on vectors looks very interesting too, I'll head over to the main site and read up on them.

    Thanks a lot

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