String 的构造函数、析构函数和赋值函数

class String
{
public:
String(const char *str=NULL);
String(const String &other);
~String(void);
String & operate =(const String &other);
private:
char *m_data;
}

String::String(cost char *str=NULL)
{
if(str == NULL)
{
m_data = new char(1);
m_data = '/0';
}
else
{
int len = strlen(str);
m_data = new char(len + 1);
strcpy(m_data, str);
}
}

String::String(const String &other)
{
if(other.m_data == NULL)
{
m_data = new char(1);
m_data = '/0';
}
else
{
int len = strlen(other.m_data);
m_data = new char(len+1);
strcpy(m_data, other.m_data);
}
}

String & String::operate =(const String &other)
{
if(this == &other.m_data)
{
return *this;
}

delete m_data;

int len = strlen(other.m_data);
m_data = new char(len + 1);
strcpy(m_data, other.m_data);

return *this;
}

String::~String(void)
{
delete [] m_data; // 由于m_data 是内部数据类型，也可以写成 delete m_data;
}