Thread: Damage error with clearing a vector

found the function that fills the vector and it seems to be causing the problems. I use almost the same code as in this function within the program and that vector can be cleared without a problem. I've been looking at it for a while but can't pin point the problem. Could someone take a look at it, I must be missing something:

Code:

void ReadDataSec(FILE * inp, FSAD &Section , int nExpected)
{
	char line[110];
	int  check;
	int newline =0, endcount=0;
	DataLine dl;

	int size = nExpected*2 +1;

	while ( fgets(line, sizeof line, inp) != NULL) // reads in a line of text from file
	{
		dl.Param = dl.Label=dl.SFactor=dl.SigBits=dl.Bit30=dl.Bit31=dl.Max=dl.Min = '\0';
		newline =0;

		if (strncmp(line, "\n", 1) == 0)
			newline =1;

		check = (sscanf(line, "%s %d %f %d %d %d %f %f", dl.Param, &dl.Label,
                   &dl.SFactor, &dl.SigBits, &dl.Bit30, &dl.Bit31, &dl.Max, &dl.Min)); 
		
		if ( strncmp(dl.Param, "ENDL", 4) == 0 && newline ==0) // Exit if at the end of a section
		{
			dl.Label=dl.SFactor=dl.SigBits=dl.Bit30=dl.Bit31=dl.Max=dl.Min='\0';
			
			Section.vectDL.push_back(dl);
			break;
         }

		if ( strcmp(dl.Param, "END") == 0 && newline == 0) // set all fields to 0 
at the end of subsection marker
		{
			dl.Label=dl.SFactor=dl.SigBits=dl.Bit30=dl.Bit31=dl.Max=dl.Min='\0';
			
			Section.vectDL.push_back(dl);
			
			endcount++;
		}

		if (strncmp(dl.Param, "END", 3) != 0 && newline ==0) // If the line is not
 the end of subsection marker, copy the line into global vector
		{
			
			if (check == 8)
			{	
				Section.vectDL.push_back(dl);
			}

			else if (check == 6)
			{
				dl.Max=dl.Min='\0';

				Section.vectDL.push_back(dl);
			}
		}

		
	}

	if (endcount != nExpected)
		EXIT_FAILURE;
}

The orange line in the above code was removed, and the error does not occure anymore. However, the file is not parsed properly now. I hope it won't take me another million hours to fix that.

I just don't understand why would resettign the structure variable would cause a amemory leak?

> dl.Param = dl.Label=dl.SFactor=dl.SigBits=dl.Bit30=dl.Bit31=d l.Max=dl.Min = '\0';
You should not be setting dl.Param to '\0'. Since this is a char array (assumption based on your sscanf()), you would lose the memory address. To clear dl.Param, use:

Code:

dl.Param[0] = '\0';

And since dl.Label and the rest are numbers, you should zero them with:

Code:

... = 0;

instead of:

Code:

... = '\0';

The two statements are equivalent, but the second is usually used for strings.

dl.Param is a CString.

and I'm using MS VC++ 6.0

I've amde the change from '\0' to 0, but I kept getting the demage error. So I figured that if I can't fix this problem I'll go around it. So I used an array of dl's instead of reusing and resetting the same one. This way I only use the data I just read into that cell and there is no demage error further on. That array is destryed automatically on the stack, so I don't have to worry about it.
I have to admit I really don't understand how clearing that variable would cause a demage problem with the vector being filled later on.

I don't believe it's a good idea to pass a CString directly to sscanf(). I would try something like:

Code:

check = (sscanf(line, "%s %d %f %d %d %d %f %f", dl.Param.GetBufferSetLength(sizeof(line)), &dl.Label,
                   &dl.SFactor, &dl.SigBits, &dl.Bit30, &dl.Bit31, &dl.Max, &dl.Min));

And then just leave out dl.Param in your clearing line:

Code:

dl.Label=dl.SFactor=dl.SigBits=dl.Bit30=dl.Bit31=dl.Max=dl.Min = 0;

Then I cannot call any other cString function until I call ReleaseBuffer(). and I'd like to work with it before I release it.

>Then I cannot call any other cString function until I call ReleaseBuffer()
I don't think that's true with GetBufferSetLength(), only with GetBuffer().

But irregardless, CString is a class, and cannot be passed directly to sscanf(). You can read a CString like a char array, but not write to one as a char array.

OK. I see. that makes a lot of sense, I always froget about it being a class in these cases.

Thanks.