直接贴代码吧，这段时间准备面试也正好练习了一下。

class String{public:    String(const char *str = "");    ~String(void);    String(const String &other);    String &operator =(const String &other);    size_t size(void) const;    const char *c_str(void);    private:    char *m_str;};String::String(const char *str){    int len = strlen(str);    m_str = new char[len + 1];    strcpy(m_str, str);}String::~String(void){    delete []m_str;}String::String(const String &other){    int len = strlen(other.m_str);    m_str = new char[len + 1];    strcpy(m_str, other.m_str);}String& String::operator=(const String &other){    if (other == *this)        return *this;    delete []m_str;    int len = strlen(other.m_str);    m_str = new char[len + 1];    strcpy(m_str, other.m_str);    return *this;}size_t String::size(void){    return strlen(m_str);}const char* String::c_str(void){    return m_str;}