Implement string class

str.cpp

#include <iostream>
#include <cstring>

#include "str.h"

namespace str {

    str::str() : buffer(0) {}

    str::~str() { delete[] this->buffer; }

    str::str(const char *src) {
        buffer = new char[strlen(src) + sizeof ""];
        strcpy(buffer, src);
    }

    str::str(const str &src) {
        buffer = new char[strlen(src.buffer) + sizeof ""];
        strcpy(buffer, src.buffer);
    }

    str &str::operator=(const char *p) {
        delete[] this->buffer;
        this->buffer = new char[strlen(p) + sizeof ""];
        strcpy(this->buffer, p);
        return *this;
    }

    str &str::operator=(const str &p) {
        delete[] this->buffer;
        this->buffer = new char[strlen(p.buffer) + sizeof ""];
        strcpy(this->buffer, p.buffer);
        return *this;
    }

    str str::operator+(const char *other) const {
        str res;
        res.buffer = new char[strlen(this->buffer) + strlen(other) + sizeof ""];
        strcpy(res.buffer, this->buffer);
        strcat(res.buffer, other);
        return res;
    }

    str str::operator+(const str &other) const {
        str res;
        res.buffer = new char[strlen(this->buffer) + strlen(other.buffer) + sizeof ""];
        strcpy(res.buffer, this->buffer);
        strcat(res.buffer, other.buffer);
        return res;
    }

    char str::operator[](int idx) const {
        return this->buffer[idx];
    }

    str::operator const char *() const {
        return this->buffer;
    }

    int str::size() const {
        int i = 0;
        while (this->buffer[i]) ++i;
        return i;
    }

    extern "C" void init() {
        str x = "DOCTOR";
        str y = " WHO";
        str z = "?";
        str t = x + y + z;
        printf("Full str: %s\nIndexed: ", (const char *) t);
        for (int i = 0; i < t.size(); ++i)
            printf("%c ", t[i]);
    }
}

int main() {

    str::init();

    return 0;
}

str.h

#ifndef STR_H

#define STR_H

namespace str {
    struct str {
    public:
        str();

        str(const char *);

        str(const str &);

        ~str();

        str operator+(const str &) const;

        str operator+(const char *) const;

        str &operator=(const str &);

        str &operator=(const char *);

        char operator[](int idx) const;

        operator const char *() const;

        int size() const;

    private:
        char *buffer;
    };
}
#endif // STR_H