Dynamic String Array Container Class hangs on runtime at delete[]

Question

I am working on an assignment to create a container class for a dynamic array of strings. I know this would be far better done with a std::vector, but that is not the 'pointer' of the assignment.

From what I can tell, my program hangs during the delete [] lineArray step below.

MyBag::MyBag()
{
    nLines = 0;
    lineArray = new std::string[0] ();
}
void MyBag::ResizeArray(int newLength)
{
    std::string *newArray = new std::string[newLength];
    //create new array with new length
    for (int nIndex=0; nIndex < nLines; nIndex++)
    {
        newArray[nIndex] = lineArray[nIndex];
        //copy the old array into the new array
    }
    delete[] lineArray; //delete the old array
    lineArray = newArray; //point the old array to the new array
    nLines = newLength; //set new array size
}
void MyBag::add(std::string line)
{
    ResizeArray(nLines+1); //add one to the array size
    lineArray[nLines] = line; //add the new line to the now extended array
    nLines++;
}

The entire program is here http://pastebin.com/KnL4XmAw

At what point does it crash? On the first `add()` call? We don't have the input file, so even with the full code we can't tell when the crash occurs. — Chad, May 13 '13 at 18:11
A couple of things to consider: 1) what happens if `newLength` is less than the string's current length? 2) Follow the [rule of three](http://en.wikipedia.org/wiki/Rule_of_three_%28C%2B%2B_programming%29). — juanchopanza, May 13 '13 at 18:13

score 3 · Answer 1 · answered May 13 '13 at 18:22

ResizeArray(nLines+1); //add one to the array size
lineArray[nLines] = line; //add the new line to the now extended array
nLines++;

The call to ResizeArray has already adjusted the value of nLines. The increment in the last line is wrong, as is the use of lineArray[nLines] in the next to last line.

score 1 · Accepted Answer · edited May 23 '17 at 12:13

A problem is in add:

ResizeArray(nLines+1); //add one to the array size - INCREMENTS nLines
lineArray[nLines] = line; //add the new line AFTER THE END OF the now extended array
nLines++;                 //add another one to the array size - WRONG

This should be:

ResizeArray(nLines+1); //add one to the array size
lineArray[nLines-1] = line; //add the new line to the now extended array

Also, if you're writing a class to manage dynamic resources like this, make sure you consider the Rule of Three. Yours will go horribly wrong if you ever copy it.

Dynamic String Array Container Class hangs on runtime at delete[]

2 Answers2