Question

i wrote a class named octed_string , without a destructor it works well but with that it could not return any octed_string type in function.

please look at the code below and tell me what is wrong .

when i delete the destructor it work! (cout print 12)

can any one help?

class octed_string
{
private:
    uint8_t *value;
    size_t length;
    size_t allocated;
public:
    octed_string()//constructor
        :value(0),length(0),allocated(0)
    {

    }
    void copy(uint8_t *from, uint8_t *to)
    {
        for (size_t i = 0; i < length; i++)
            *to++ = *from++;
    }

    void allocate()
        {
            if (value == 0)
            {
                allocated = STACK_INITIAL_ALLOC;
                value = new uint8_t[allocated];
            }
            else
            {
                // We need to allocate more memory

                size_t new_allocated = allocated + STACK_CHUNK_ALLOC;
                uint8_t *new_value = new uint8_t[new_allocated];

                // Copy from old stack to new stack
                copy(value, new_value);

                // Delete the old value
                delete [] value;

                allocated = new_allocated;
                value = new_value;
            }
        }

    ~octed_string()//destructor
    {
        if(value)
            delete [] value;
    }

    friend ostream &operator<<(ostream &_output,const octed_string &_str)//opration overloading for cout
    {
        for(int i=0;i<_str.length;i++)
            _output<<(uchar_t)_str.value[i];
        return _output;
    }

    void add(uint8_t input)//this function automatically add space to value (new)
    {
        if (length == allocated)
            allocate();  // Allocate more memory

        value[length++] = _value;
    }

    octed_string sub_string(int start,int end)//( this function has a problem with destructor i think because it return octed_string)
    {
        octed_string a;
        for(int i=start;i<end;i++)
            a.add(a);
        return a;
    }
};

void main()
{
    octed_string o; //object
    o.add(1);
    o.add(2);
    o.add(3);

    cout<<o.sub_string(0,2); //i expect printing 12 but i does not!
}

———————–//answer
thanks to phresnel it fix by adding following codes:

octed_string(const octed_string &_input)
    :value(0),length(0),allocated(0)
{
    while(length<_input.length)
    {
        this->add((uchar_t)_input[length]);
    }
}

octed_string& octed_string::operator= (octed_string const& _in)
{
    octed_string tmp(_in);
    return *this;
}

but i still can not understand the reason. could any body show any reference to learn this issue?

Answer 1

You need to define a copy constructor, and assignment operator, for octed_string.

When you do not have a destructor it works because the memory allocated for member variable value is not destroyed and the copy constructed by the default copy constructor refers to the same undeleted memory that original, now destroyed, object did.

When you do have a destructor the memory is deleted.

The copy is created when sub_string() returns.