Printing out an object of array's members error

Question

I'm having a little bit of trouble printing out a member of my struct. This is what I have so far:

struct Code
{
  char letter;
  string sequence;
}

void createCode(HuffmanNode *root, string codestr, Code *codeBook, int count)
{
  if(root->getRight() == NULL && root->getLeft() == NULL)
  {
    Code code;
    code.letter = root->getLetter();
    code.sequence = codestr;
    codeBook[count] = code;
    count++;
  }
  else
  {
    createCode(root->getLeft(), codestr + "1", codeBook, count);
    createCode(root->getRight(), codestr + "0", codeBook, count);
  }
}

This works all fine, but in main when I try to print out the member sequence in my array of Codes in Codebook:

string codestr;
count = 0;
Code codeBook[256];
createCode(root, string codestr, codeBook, count); //root is already created 
for(int i = 256; i >= 0; i--)
{
  if(isalpha(codeBook[i].letter))
  cout << codeBook[i].sequence << " ";
}

Only the last string I stored is printed. Might anyone know a fix and why this is happening? If anyone could help, that'd be great!

NPE · Accepted Answer · 2012-12-01 07:25:50Z

1

The main problem is that createCode() is always passed count=0. Because of this, you store all Code entries at the zeroth position in your array, and the last one overwrites all previous entries.

To fix, either pass count by reference or pointer, or make the function return the new value of count.

Finally, the starting value of the for loop is out of bounds (off by one).

edited Dec 1, 2012 at 7:25

answered Dec 1, 2012 at 7:20

NPE

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3 Comments

user200081 Over a year ago

Well when I call createCode() count is incremented in my if statement isnt it?

NPE Over a year ago

@user200081: Not really. You increment it in the first branch, and recursively call createCreate() in the second. You never do both.

user200081 Over a year ago

Ah that helped. Thank you! I understand what I did wrong now. I need to pass by reference...

billz · Accepted Answer · 2012-12-01 07:24:48Z

0

When you createCode, count is not incrementing, because you are passing it by value, change to pass by reference:

void createCode(HuffmanNode *root, string codestr, Code *codeBook, int& count)

array codeBook contains 256 elements but index is from 0 to 255. for loop should be:

for(int i = 255; i >= 0; i--)

Otherwise access out-of-boundry array element is undefined behavior.

edited Dec 1, 2012 at 7:24

answered Dec 1, 2012 at 7:19

billz

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2 Comments

user200081 Over a year ago

Thanks for catching that! I just fixed that but it still didn't print out correctly... any other tips?

billz Over a year ago

you shall pass count to createCode by reference

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