需要自己實現C++中的string類。

本文給出的實現包括string類的一些基本操作。

如：構造 拷貝構造 賦值 判斷相等 字串長度 []操作 字串拼接 <<序列化 swap操作等。

程式碼如下：

#include <iostream>
#include <iomanip>
#include <vector>

using namespace std;
class String
{
public:
	// 構造
	String();
	String(const char* str);
	String(const String& other);
public:
	String operator+(const String& other);
	String& operator=(const String& other);
	bool operator==(const String& otehr);

	const char& operator[](unsigned int);
	size_t size() const;
	const char* c_str() const;
	void swap(String& other);
public:
	// 過載
	friend ostream& operator<<(ostream&	out, const String& other);
	friend istream& operator>> (istream&, String&);
	// 析構
	~String(void);

private:
	char *m_data;	// 儲存字串值
};

//1
String::String()
{
	m_data = new char[1];
	*m_data = '\0';
}

//2
String::String(const char* other)
{
	if (other == NULL)
	{
		m_data = new char[1];
		*m_data = '\0';
	}
	else
	{
		m_data = new char[strlen(other) + 1];
		strcpy(m_data, other);
	}
}

//3
String::String(const String& other)
{
	m_data = new char[other.size() + 1];
	strcpy(m_data, other.c_str());
}

//4
String& String::operator=(const String& other)
{
	if (this != &other)
	{
		delete[] m_data;
		m_data = new char[other.size() + 1];
		strcpy(m_data, other.c_str());
	}
	return *this;
}

//5
size_t String::size() const
{
	return strlen(m_data);
}

//6
const char* String::c_str() const
{
	return m_data;
}

//7
void String::swap(String& other)
{
	std::swap(m_data, other.m_data);
}

//8
String::~String()
{
	delete[] m_data;
}

//9
bool String::operator==(const String& other)
{
	if (strlen(m_data) != other.size())
	{
		return false;
	}

	return strcmp(m_data, other.c_str()) ? false : true;
}

//10
String String::operator+(const String& other)
{
	String resString;
	if (!other.m_data)
	{
		resString = *this;
	}
	else if (!m_data)
	{ 
		resString = other;
	}
	else
	{
		resString.m_data = new char[other.size() + this->size() + 1];
		strcpy(resString.m_data, m_data);
		strcat(resString.m_data, other.c_str());
	}

	return resString;
}

//11
const char& String::operator[](unsigned int idx)
{
	if (0 <= idx && idx <= this->size())
	{
		return m_data[idx];
	}
	else
	{
		//return '\0';
		// 這裡可以丟擲異常
	}
}

// 12
ostream& operator<<(ostream& out, const String& other)
{
	out << other.c_str();
	return out;
}

//13
istream& operator>> (istream& in, String& res)
{
	char tmp[255];
	in >> setw(255) >> tmp;
	res = tmp;

	return in;
}

void fun1(String s)
{

}

void fun2(const String& s)
{

}

String fun3()
{
	String tmp("fun3");
	return tmp;
}

int main(void)
{
	String s0;
	String s1("s1");
	cout << "s1 = " << s1 << endl;
	String s2(s0);
	String s3 = s1;
	s2 = s1;
	cout << "s2 = " << s2 << endl;
	cout << "s3 = " << s3 << endl;

	fun1(s1);
	cout << "s1 = " << s1 << endl;
	fun2(s1);
	cout << "s1 = " << s1 << endl;
	fun1("TEST FUN1");
	cout << "s1 = " << s1 << endl;
	fun2("TEST FUN2");
	cout << "s1 = " << s1 << endl;
	String s4 = fun3();
	cout << "s4 = " << s4 << endl;

	std::vector<String> svec;
	svec.push_back(s0);
	svec.push_back(s1);
	svec.push_back(fun3());
	svec.push_back("Last Element");

	for (auto& v: svec)
	{
		cout << v << endl;
	}

	cout << "s1 + s3 = " << (s1 + s3) << endl;

	if (s1 == s3)
	{
		cout << "s1 = s3" << endl;
	}
	else
	{
		cout << "s1 != s3" << endl;
	}

	cout << "s1[2] = " << s1[1] << endl;

	swap(s1, String("s1 swap"));
	cout << "s1 after swap = " << s1<<endl;

	return 0;
}