string的简单实现

创造一个string的对象，含有char*str和一下基本成员函数

class String
{ //友原重载<<和>>
	friend ostream& operator<<(ostream& out, const String& s);
	friend istream& operator>>(istream& in, String& s);
public:
	String() {
		str = new char[100];
		str[0] = '\0';
	}//string的默认构造
	String(const char* other)
	{
		str = new char[strlen(other) + 1];
		strcpy(str, other);
	}//有参构造
	~String()
	{
		delete[]str;
	}//析构
	String(const String& other);//复制构造
	int Length();//字符串的长度
	String& operator=(const String& other);
	String& operator=(const char* ch);//重载=
	String operator+(const String& other);//重载+
	String& operator+=(const String& other);//重载+=
	char& operator[](int x);//重载[]
	bool operator==(const String& other);//重载==
	bool operator<(const String& other);//重载<
private:
	char* str;
};

下面逐步写出每个成员函数

friend ostream& operator<<(ostream& out, const String& s);
friend istream& operator>>(istream& in, String& s);

ostream& operator<<(ostream& out, const String& s)
{
	out << s.str;
	return out;
}
istream& operator>>(istream& in, String& s)
{
	char ch[1000];//临时创造一个数组储存输入值
	in >> ch;
	delete[]s.str;//释放s的空间
	s.str = new char[strlen(ch) + 1];//为s重新分配新的空间
	strcpy(s.str, ch);//赋值给s
	return in;
}

String(const String& other);

String::String(const String& other)
{
	str = new char[strlen(other.str) + 1];
	strcpy(str, other.str);
}

int Length();

int String::Length()
{
	return strlen(str);//返回str的长度
}

String& operator=(const String& other);
String& operator=(const char* ch);

String& operator=(const String& other)
	{
		if (this != &other)//判断是否和原来一样，一样直接返回原值
		{
			delete[]str;
			str = new char[strlen(other.str) + 1];
			strcpy(str, other.str);
		}
		return *this;
	}//重载与string的=
	String& operator=(const char* ch)
	{
		delete[]str;
		str = new char[strlen(ch) + 1];
		strcpy(str, ch);
		return *this;
	}//重载与字符串的=

String operator+(const String& other);

String operator+(const String& other)
	{
		int len = strlen(str) + strlen(other.str) + 1;
		//求出需要开辟空间的大小
		char* newstr = new char[len];//用一个新指针去接收
		strcpy(newstr, str);
		strcat(newstr, other.str);
		return String(newstr);
	}//重载+

String& operator+=(const String& other);

String& operator+=(const String& other)
	{
		*this = *this + other;
		return *this;
	}//使用重载后的=和+完成+=的重载

char& operator[](int x);
bool operator==(const String& other);
bool operator<(const String& other);

	char& operator[](int x)
	{
		assert(x >= 0 && x <= strlen(str));
		//使用断言判断是否在范围内
		return str[x];
	}//重载[]
	bool operator==(const String& other)
	{
		return !strcmp(str, other.str);
	}//重载==
	bool operator<(const String& other)
	{
		return strcmp(str, other.str) < 0;
	}//重载<

完整代码及样例的使用

#define _CRT_SECURE_NO_WARNINGS
#include 
#include 
#include 
using namespace std;
class String
{ //友原重载<<和>>
	friend ostream& operator<<(ostream& out, const String& s);
	friend istream& operator>>(istream& in, String& s);
public:
	String() {
		str = new char[100];
		str[0] = '\0';
	}//string的默认构造
	String(const char* other)
	{
		str = new char[strlen(other) + 1];
		strcpy(str, other);
	}//有参构造
	~String()
	{
		delete[]str;
	}//析构
	String(const String& other);//复制构造
	int Length();//字符串的长度
	String& operator=(const String& other)
	{
		if (this != &other)
		{
			delete[]str;
			str = new char[strlen(other.str) + 1];
			strcpy(str, other.str);
		}
		return *this;
	}//重载与string的=
	String& operator=(const char* ch)
	{
		delete[]str;
		str = new char[strlen(ch) + 1];
		strcpy(str, ch);
		return *this;
	}//重载与字符串的=
	String operator+(const String& other)
	{
		int len = strlen(str) + strlen(other.str) + 1;
		char* newstr = new char[len];
		strcpy(newstr, str);
		strcat(newstr, other.str);
		return String(newstr);
	}//重载+
	String& operator+=(const String& other)
	{
		*this = *this + other;
		return *this;
	}//使用重载后的=和+完成+=的重载
	char& operator[](int x)
	{
		assert(x >= 0 && x <= strlen(str));
		return str[x];
	}//重载[]
	bool operator==(const String& other)
	{
		return !strcmp(str, other.str);
	}//重载==
	bool operator<(const String& other)
	{
		return strcmp(str, other.str) < 0;
	}//重载<
private:
	char* str;
};
String::String(const String& other)
{
	str = new char[strlen(other.str) + 1];
	strcpy(str, other.str);
}
ostream& operator<<(ostream& out, const String& s)
{
	out << s.str;
	return out;
}
istream& operator>>(istream& in, String& s)
{
	char ch[1000];
	in >> ch;
	delete[]s.str;
	s.str = new char[strlen(ch) + 1];
	strcpy(s.str, ch);
	return in;
}
int String::Length()
{
	return strlen(str);
}
int main()
{
	String s1("Help!"), s2("Good!"), s3(s2), s4, s5;
	cout << "s1=" << s1 << endl;
	s3 = "Hello!";
	cout << "s3=" << s3 << endl;
	s3 = s2;
	cout << "s3=" << s3 << endl;
	s3 += s2;
	cout << "s3=" << s3 << endl;
	cin >> s4;
	cout << "s4=" << s4 << endl;
	s5 = s3 + s4;
	cout << "s5=" << s5 << endl;
	s5[0] = 'g';
	cout << "s5=" << s5 << endl;
	cout << "strlen(s5)=" << s5.Length() << endl;
	cout << boolalpha << (s3 == s1) << endl;
	//利用boolalpha来断真假
	cout << boolalpha << (s3 < s1) << endl;
}

运行结构