What the Copy constructor does for dynamic allocations

Question

I am very curious why the copy constructor is so important for dynamically highlighting my own specific class.

I am implementing a low-level c-string class with dynamic allocations, and here is a brief overview of my class

class String
{
private:
    char * buf;
    bool inBounds( int i )
    {
        return i >= 0 && i < strlen(buf);
    }
    static int strlen(const char *src)
    {
        int count = 0;
        while (*(src+count))
            ++count;
        return count;
    }
    static char *strcpy(char *dest, const char *src)
    {
        char *p = dest;
        while( (*p++ = *src++));
        return dest;
    }
    static char* strdup(const char *src)
    {
        char * res = new_char_array(strlen(src)+1);
        strcpy(res,src);
        return res;
    }
    static char * new_char_array(int n_bytes)
    {
        return new char[n_bytes];
    }
    static void delete_char_array( char* p)
    {
        delete[] p;
    }

public:
    /// Both constructors should construct
    /// this String from the parameter s
    String( const char * s = "")
    {
        buf = strdup(s);
    }
    String( String & s)
    {
        buf = strdup(s.buf);
    }
    void reverse()
    {
    }
    void print( ostream & out )
    {
        out << buf;
    }
    ~String()
    {
        delete_char_array(buf);
    }
};
ostream & operator << ( ostream & out, String str )
{
    str.print(out);
    return out;
}

I know that part of the strdup () function is not entirely correct, but I'm just doing a few tests.

My problem is that I don't have a copy constructor, and my main () is

int main()
{
    String b("abc");
    String a(b);
    cout << b << endl;
    return 0;
}

The compiler will tell me double free or corruption (fasttop), and I will find the answers to this question and look at the rules of the Big Three.

Can you guys tell me why my code works without any errors if I have a copy constructor and what does the double release or corruption error (fasttop) mean?

Answer 1

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