Slow CString creation

After I collect up to 600,000 points of data I have to process each point into a text string and display it in an edit control and/or save it as a text file, but as I process the string the processing gets very slow very soon. I update the process after every 2k points and it gets noticabley slower after each set, untill after 10,000 it is unacceptably slow.

What is going on and what can I do to remedy?



for( i=0; i<m_DataCount; i++ )
	{
		MSG msg;
		while( ::PeekMessage( &msg, NULL, 0, 0, PM_NOREMOVE ) )
		{
			AfxGetApp()->PumpMessage();  // does a ::GetMessage() (waits...)
		}
// VOLTAGE
		cdword._dword = dwArray[i];
		wVoltage = cdword.word1;
		if( wVoltage < 100 )
			break;
	// CURRENT
		wCurrent = cdword.byte1 & 0xFC;
 
		f = wVoltage;
		str.Format("%.3f\t", f / 1000 );
		strData += str;
 
		j = wCurrent;
		f = j;
		str.Format("%.3f\t", f / 100 );
		strData += str;
 
		j = wTemperature;
		str.Format("%d\r\n", j);
		strData += str;
 
		if( i % 2000 == 0 )
		{
			str.Format("Logging complete\r\n\r\nProcessing data please wait... %dk points", i /1000 );
			m_editData.Clear();
			m_editData.SetWindowText( str );
		}
	}
	m_editData.SetWindowText( strData );

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EnergyStorageAsked:
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AndyAinscowConnect With a Mentor Freelance programmer / ConsultantCommented:
strData += str

As the contents of strData are continually growing I suspect you have memory allocation/copy problems.

Reduce the number of times you perform the 'strData += str' action.
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EnergyStorageAuthor Commented:
I knew it was due to the constant changing of CString buffer size and I solved it myself using CString function GetBufferSetLength.

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AndyAinscowFreelance programmer / ConsultantCommented:
excerpt of question
>>What is going on

later comment by questioner after a comment suggesting where the problem could lie and a solution
>>I knew it was due to the constant changing of CString buffer size

Seems to be some mismatch of information in those two statements.
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EnergyStorageAuthor Commented:
a21748945 was not a solution.

I said "What is going on and how do I remedy this. Not Doing what need to be done is not a remedy.

I found the remedy on my own as I said above by using the CString function GetBufferSetLength().

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AndyAinscowFreelance programmer / ConsultantCommented:
In your original question you stated you did NOT know what was slow in your code.  When you know that then you can then remedy it.
I pointed out what I thought was slow and one potential change to improve the performance.
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