后台面试经典问题-string类实现

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class String{
public:
	String(const char *str=NULL);
	String(const String &str);

	~String();

	String& operator=(const String &str);

private:
	char* data;
	size_t length;
};


String::String(const char *str)
{
	if(!str)
	{
		length=0;
		data = new char[1];
		*data='\0';
	}

	else
	{
		length=strlen(str);
		data=new char[length+1];
		strcpy(data, str);
	}
}


String::String(const String &str)
{
	length=str.size();
	data=new char[length+1];
	strcpy(data,str.c_str());
}


String::~String()
{
	delete []data;
	length=0;
}


String& String::operator=(const String &str)
{
	if(this==&str)
		return *this;

	delete []data;
	length = str.size();
	data = new char[length+1];
	strcpy(data, str.c_str());

	return *this;
}