C/C++学习笔记：String类的构造函数、析构函数和赋值函数

已知：String 类 

class String 
{ 
public: 
      String(const char *str = NULL); // 通用构造函数
     String(const String &another); // 拷贝构造函数
     ~ String(); // 析构函数
     String& operator=(const String &rhs); // 赋值函数
private: 
     char *m_data; // 用于保存字符串
}; 

#include <iostream>class String{public:String (const char *str = NULL); //通用构造函数String (const String &another);  //拷贝构造函数~String();  //析构函数String& operator = (const String &rhs); //赋值函数protected:private:char *m_data; //用于保存字符串};String::String(const char *str){if ( NULL == str){m_data = new char[1];  ////对空字符串自动申请存放结束标志'\0'的空间if ( NULL == m_data )  //内存是否申请成功{std::cout << "Application of memory failure" << std::endl;exit(1);}m_data[0] = '\0';}else{int length = strlen(str);m_data = new char[length + 1];if (NULL == m_data){std::cout << "Application of memory failure" << std::endl;exit(1);}strcpy(m_data, str);}}String::String(const String &another)  //输入参数为const型 {int length = strlen(another.m_data);m_data = new char[length + 1];if (NULL == m_data){std::cout << "Application of memory failure" << std::endl;exit(1);}strcpy(m_data, another.m_data);}//析构函数String::~String(){delete [] m_data;}String& String::operator=(const String &rhs)  //输入参数为const型 {if ( this == &rhs ) //检查自赋值 {  return *this;}int length = strlen(rhs.m_data);delete [] m_data;//释放原来的内存资源m_data = new char[length+1];if (NULL == m_data){std::cout << "Application of memory failure" << std::endl;exit(1);}strcpy(m_data, rhs.m_data);return *this;  //返回本对象的引用}// 测试void main(){String A;String B("CSDN");system("pause");}

引申：用C++实现一个String类，它具有比较，连接，输入，输出功能，并且提供一些测试用例。

//String.h#ifndef STRING_H#define STRING_H#include<iostream>using namespace std;class String{public:String();//默认构造函数String(int n, char c); //普通构造函数String(const char* source); //普通构造函数String(const String& s); //复制构造函数String& operator= (char* s);  //重载=，实现字符串赋值String& operator= (const String& s);  //重载=，实现对象赋值~String();   //析构函数char& operator[] (int i);//重载[]，实现数组运算const char& operator[] (int i) const;//重载[]，实现数组运算（对象为常量）String& operator+= (const String& s); //重载+=，实现与对象相加String& operator+= (const char* s); //重载+=，实现与字符串相加friend ostream& operator<< (ostream& out, String& s);//重载<<，实现输出流friend istream& operator>> (istream& in, String& s);  //重载>>，实现输入流friend bool operator< (const String& left, const String& right);   //重载<friend bool operator> (const String& left, const String& right);//重载>friend bool operator== (const String& left, const String& right); //重载==friend bool operator!= (const String& left, const String& right); //重载!=char* getData();//获取data指针int length();private:int size;  //长度char* data;   //指向字符串数据};#endif

//String.cpp#include "String.h"String::String(){data = new char[1];*data = '\0';size = 0;}String::String(int n, char c){data = new char[n + 1];size = n;char* tmp = data;while( n -- ){*tmp++ = c;}*tmp = '\0';}String::String(const char* source){if( NULL == source){data = new char[1];*data = '\0';size = 0;}else{size = strlen(source);data = new char[size + 1];strcpy(data, source);}}String::String(const String& s){data = new char[s.size + 1];strcpy(data, s.data);size = s.size;}String& String::operator=(char* s){if (NULL != data){delete [] data;}size = strlen(s);data = new char[size + 1];strcpy(data, s);return *this;}String& String::operator=(const String& s){if( this == &s ){return *this;}if(NULL != data){delete[] data;}size = strlen(s.data);data = new char[size + 1];strcpy(data, s.data);return *this;}String::~String(){if( NULL != data){delete[] data;data = NULL;size = 0;}}char& String::operator[](int i){return data[i];}const char& String::operator[](int i) const{return data[i];}String& String::operator+=(const String& s){int len = size + s.size +１;char* temp = data;data = new char[len];size = len - 1;strcpy(data, temp);strcat(data, s.data);delete[] temp;return *this;}String& String::operator+=(const char* s){if( NULL == s){return *this;}int len = size + strlen(s) + 1;char* temp = data;data = new char[len];size = len - 1;strcpy(data, temp);strcat(data, s);delete[] temp;return *this;}int String::length(){return size;}ostream& operator<<(ostream& out, String& s){for( int i = 0; i < s.length(); ++i){ out << s[i] << " ";}return out;}istream& operator>>(istream& in, String& s){char p[50];in.getline(p,50);s = p;return in;}bool operator< (const String& left, const String& right){int i = 0;while(left[i] == right[i] && left[i] != 0 && right[i] != 0){i ++;}return left[i]-right[i] < 0 ? true:false;}bool operator> (const String& left, const String& right){int i = 0;while(left[i] == right[i] && left[i] != 0 && right[i] != 0){i ++;}return left[i]-right[i] > 0 ? true:false;}bool operator== (const String& left, const String& right){int i = 0;while(left[i] == right[i] && left[i] != 0 && right[i] != 0){i ++;}return left[i]-right[i] == 0 ? true:false;}bool operator!= (const String& left, const String& right){int i = 0;while(left[i] == right[i] && left[i] != 0 && right[i] != 0){i ++;}return left[i]-right[i] != 0 ? true:false;}