c++ inseting User Defined class into map - c++

Question

I've been looking around for quite some time and think I have most of the pieces together but my code still won't work...
I have a map,
map<Number, Entry> chainList;
and a class Number and Entry, the Entry we wont worry about for now as I'm pretty sure that half works correct
in Number.h
class Number
{
public:
//Public Functions
//Constructor/Destructor
Number(int len);
Number(string copy);
Number(const unsigned char *copy, int len);
Number(const Number& in);
~Number();
.......
.......
friend void swap(Number& first, Number& second);
bool operator<(const Number& rhs) const;
Number& operator=(Number &rhs);
private:
//our binary number array
unsigned char *num;
//hold the length used, and maxsize of the array
int length;
};
then,
//in Number.cpp
Number::~Number()
{
delete [] num;
}
Number::Number(const Number& in)
{
length = in.length;
num = (unsigned char *) calloc(length, sizeof(unsigned char));
for (int i = 0; i < length; i++)
{
num[i] = in.num[i];
}
}
bool Number::operator<(const Number& rhs) const
{
if (this -> length > rhs.length)
{
return false;
}
for (int i = 0; i < this -> length; i++)
{
if (this -> num[i] > rhs.num[i])
{
return false;
}
else if (this -> num[i] < rhs.num[i])
{
return true;
}
}
return false;
}
void swap(Number& first, Number& second)
{
// enable ADL (not necessary in our case, but good practice)
using std::swap;
// by swapping the members of two classes,
// the two classes are effectively swapped
swap(first.length, second.length);
swap(first.num, second.num);
}
Number& Number::operator=(Number &rhs)
{
swap (*this, rhs);
return *this;
}
however when I try and insert an item into the map I get a seg fault....
in Database.cpp
....
chainList.insert(pair<Number, Entry>(*(tempEntry -> msgHash), *tempEntry));
.....
where tempEntry -> msgHash is a Number* - dynamically allocated
what could my issue be? another option is I have a function that typecasts and returns a c++ string, my question is will the std::less_than function work with null characters in the middle of the statement, I know it works in lexigraphical order but is it up to the first null?

Answer 1

I think the problem is in operator<():
if (this->length > rhs.length)
return false;
for (int i = 0; i < rhs.length; i++)
....
See? If rhs.length is greater than this->length you go on and compare the bytes. But you compare up to rhs.length bytes, and that might overflow this->num, as this->length is less or equal to rhs.length.
I'm not sure if you need a specific sorting order, but I would do something like:
if (this->length > rhs.length)
return false;
if (this->length < rhs.length)
return true;
for (int i = 0; i < rhs.length; i++)
....
Now, when you reach the loop you are sure that both arrays are the same length.
UPDATE:
You have another important issue in operator=(Number &rhs). This operator should never modify the right-hand-side operator. So it should be operator=(const Number &rhs) or operator=(Number rhs), but never a non-const reference, as yours is.
You are trying to implement the copy-and-swap idiom. You got it almost right, the proper way is:
Number& Number::operator=(Number rhs)
{
swap (*this, rhs);
return *this;
}
UPDATE #2:
You are allocating your array with calloc() but freeing it with delete[]. That is undefined behaviour. Memory allocated with calloc() is freed with free(), and memory allocated with new[] is freed with delete[].
My advice is to use std::vector<unsigned char> to hold dynamic arrays, and avoid all the this->length, delete[], etc. Just do std::swap() on the vectors and it's done.