Implementation of small string optimization

my_string.cpp

#include <cstring>
#include <cstdio>

class my_string
{
private:
  union
  {
    char inline_buf[16]; // sso
    char *bufptr;
  } data_;
  unsigned int size_;

public:
  my_string()
    : size_(0)
  {}

  my_string& operator=(const char *cstr)
  {
    resize(std::strlen(cstr)+1);
    if (size_ <= 16)
      std::memcpy(data_.inline_buf, cstr, size_);
    else
      std::memcpy(data_.bufptr, cstr, size_);
    return *this;
  }

  const char& operator[](int i) const
  { 
     if (size_ <= 16)
      return data_.inline_buf[i];
    else
      return data_.bufptr[i];
  }

  void resize(int size)
  {
    if (size_ > 16)
      delete[] data_.bufptr;

    size_ = size;
    if (size_ > 16)
      data_.bufptr = new char[size_];
  }

  const char *c_str() const
  {
    return &(*this)[0];
  }
};

int main()
{
  my_string str;

  str = "Das ist ein Test";
  std::printf("%s\nbuffer address: %p\n\n", str.c_str(), &str[0]);

  str = "Und noch ein langer Test";
  std::printf("%s\nbuffer address: %p\n\n", str.c_str(), &str[0]);

  str = "SSO";
  std::printf("%s\nbuffer address: %p\n\n", str.c_str(), &str[0]);

  // Possible output:
  //
  // Das ist ein Test
  // buffer address: 0x14ffc20
  // 
  // Und noch ein langer Test
  // buffer address: 0x1500050
  // 
  // SSO
  // buffer address: 0x7fffb5d3ec20

}