Huffman coding c++ - c++

Question

So I am working on Huffman coding for a project. However, my code just doesn't work. When i ran it on visual studio, it didn't give me an error. What I was trying to do is to read a file and put all of them into a string. And get the frequency for each character in that string. But I think when the file got a little bit large, it seems like my code is running in a infinite loop. Can anyone explain anything to me? By the way, I had a sorted function that I used to sort a vector of node* by their frequency.
ifstream infile;
infile.open(filename);
string q;
string line;
while (getline(infile, line))
{
q += line;
}
char y;
int count = 0;
int check = 0;
for (int i = 0; i < q.size(); i++) //if the string gets big, it seems to become an infinite loop in here
{
y = q[i];
for (int x = i - 1; x > 0; x--) //make sure not counting the same char
{
if (y == q[x])
{
check++;
}
}
if (check == 0)
{
for (int i = 0; i < q.size(); i++)
{
if (q[i] == y)
{
count++;
}
}
node*x = new node;
x->char1 = y; //my node have char
x->freq = count; //my node has frequency
list1.push_back(x);
}
count = 0;
check = 0;
}
sort(list1.begin(), list1.end(), sorter); //sort them from small to big
while (list1.size() > 1)
{
node*left = list1[0];
node*right = list1[1];
list1.erase(list1.begin(), list1.begin() + 2);
double sum = left->freq + right->freq;
node* x = new node;
x->freq = sum;
x->left = left;
x->right = right;
list1.push_back(x);
sort(list1.begin(), list1.end(), sorter);
}
list1.clear();
return true;
The following is my sort function
static struct {
bool operator()(NodeInterface* a, NodeInterface* b) {
if (a->getFrequency() == b->getFrequency()) {//if the frequencies are even,
if (b->getCharacter() == '\0') return false;
if (a->getCharacter() != '\0') {
return (int)a->getCharacter() < (int)b->getCharacter();
}
return false;
}
return a->getFrequency() < b->getFrequency();
}
} sorter;

Answer 1

I see two major problems.
You have a for loop inside a for loop both initializing and using int i
Change the variable name of the inner loop.
for (int i = 0; i < q.size(); i++) //if the string gets big, it seems to become an infinite loop in here
.
.
if (check == 0)
{
for (int i = 0; i < q.size(); i++) //Change this to int j for example
{
.
.
And the Sorter struct. I would rewrite it as this.
static struct {
bool operator()(NodeInterface* a, NodeInterface* b) {
if (a->getFrequency() == b->getFrequency()) {//if the frequencies are even,
if (b->getCharacter() == '\0') return false;
if (a->getCharacter() == '\0') return true;
return (int)a->getCharacter() < (int)b->getCharacter();
}
return a->getFrequency() < b->getFrequency();
}
} sorter;
A few suggestions for your for loop:
for (int i = 0; i < q.size(); i++) //if the string gets big, it seems to become an infinite loop in here
{
y = q[i];
//You can avoid this entire loop by using a structure like map
for (int x = i - 1; x > 0; x--) //make sure not counting the same char
{
if (y == q[x])
{
check++;
//break; //if you use a loop, break it once you find the character.
}
}
if (check == 0)
{
for (int j = 0; j < q.size(); j++)//Renamed variable + you can start this loop from j = i as you know there is no occurrence of y before that.
{
if (q[i] == y)
{
count++;
}
}
node*x = new node;
x->char1 = y; //my node have char
x->freq = count; //my node has frequency
list1.push_back(x);
}
count = 0;
check = 0;
}