String Header File

#ifndef STRING_H
#define STRING_H

#include <iostream>
#include <cstring>

class String
{
    public:
        String ();
           ~String ();
        String (const String &);
        String (String &&);
        String (const char);
        String (const char *);
        String &operator= (const String &);
        String &operator= (String &&);

        friend std::ostream &operator<< (std::ostream &, const String &);
        friend std::istream &operator>> (std::istream &, String &);
        friend String operator+ (const String &, const String &);

    private:
        size_t str_ctored_size = 0;
        size_t edge = 20;
            char * str = nullptr;

        inline void free ();
        inline void allocate (size_t);
        inline void destruct ();
};

#endif