【C++ Primer Plus习题】12.2

本文主要是介绍【C++ Primer Plus习题】12.2，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

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问题:

解答:
main.cpp

#include <iostream>
#include "String.h"
using namespace std;int main()
{String s1(" and I am a C++ student.");String s2 = "Please enter your name: ";String s3;cout << s2;cin >> s3;s2 = "My name is " + s3;cout << s2 << ".\n";s2 = s2 + s1;s2.stringup();cout << "The string\n" << s2 << "\ncontains " << s2.has('A') << " 'A' characters in it.\n";s1 = "red";String rgb[3] = { String(s1),String("green"),String("blue") };cout << "Enter the name of a primary color for mixing light: ";String ans;bool success = false;while (cin >> ans){ans.stringlow();for (int i = 0; i < 3; i++){if (ans == rgb[i]){cout << "That's right!\n";success = true;break;}}if (success)break;else cout << "Try again!\n";}cout << "Bye!" << endl;return 0;return 0;
}

String.h

#pragma once
#include <iostream>
using namespace std;class String
{
private:char* str;int len;static int num_strings;static const int CINLIM = 80;
public:String();String(const char*s);String(const String&s);~String();int lengh()const { return len; }String& operator=(const String&s);String& operator=(const char*s);char& operator[](int i);const char& operator[](int i)const;void stringup();void stringlow();int has(char c);String operator+(const String& s);bool operator==(const String& s);friend bool operator<(const String& st1, const String& st2);friend bool operator>(const String& st1, const String& st2);friend ostream& operator<<(ostream& os, const String& s);friend istream& operator>>(istream& is, String& s);friend String operator+(const char* c, const String& s);static int HowMany();
};

String.cpp

#include "String.h"
#include <cctype>int String::num_strings = 0;int String::HowMany()
{return num_strings;
}String::String()
{//str = NULL;//len = 0;len = 4;str = new char[1];str[0] = '\0';num_strings++;
}
String::String(const char* s)
{len = strlen(s);str = new char[len+1];strcpy_s(str, len+1, s);num_strings++;
}String::String(const String&s)
{len = s.len;str = new char[len + 1];strcpy_s(str, len + 1, s.str);num_strings++;
}String::~String()
{--num_strings;delete[] str;
}String& String::operator=(const String& s)
{if (this == &s)return *this;if (str)delete[] str;len = s.len;str = new char[len + 1];strcpy_s(str, len + 1, s.str);return *this;
}String& String::operator=(const char* s)
{if (str)delete[] str;len = strlen(s);str = new char[len + 1];strcpy_s(str, len + 1, s);return *this;
}char& String::operator[](int i)
{return str[i];
}
const char& String::operator[](int i)const
{return str[i];
}void String::stringup()
{for (int i = 0; i < len;i++){str[i] = toupper(str[i]);}
}
void String::stringlow()
{for (int i = 0; i < len; i++){str[i] = tolower(str[i]);}
}
int String::has(char c)
{int count = 0;for (int i = 0; i < len; i++){if (str[i] == c){count++;}}return count;
}String String::operator+(const String& s)
{/*if (!s.str || !str)return String();int size = strlen(s.str) + strlen(str) + 1;char* result = new char[size];strcpy_s(result, strlen(str) + 1, str);strcat_s(result,size, s.str);return String(result);*/String result;result.len = s.len + len;result.str = new char[result.len + 1];strcpy_s(result.str, result.len+1 ,str);strcat_s(result.str, result.len + 1, s.str);return result;
}bool operator<(const String& st1, const String& st2)
{return strcmp(st1.str, st2.str) < 0;
}
bool operator>(const String& st1, const String& st2)
{return st2 < st1;
}
bool String::operator==(const String& s)
{bool flag = false;for (int i = 0; i < len; i++){if (str[i] == s.str[i]){flag = true;}else{return false;}	}return flag;
}ostream& operator<<(ostream& os, const String& s)
{os << s.str;return os;
}//istream& operator>>(istream& is, String& s)
//{
//	char* str=NULL;
//	is >> str;
//	s.str = new char[strlen(str) + 1];
//	strcpy_s(s.str, strlen(str) + 1, str);
//	return is;
//}istream& operator>>(istream& is, String& s) {char buffer[256]; // 使用一个临时缓冲区  //is >> buffer; // 读取输入到缓冲区 is.getline(buffer, 256);// 释放之前的内存（如果有）  delete[] s.str;// 分配新的内存并复制字符串  s.len = strlen(buffer);s.str = new char[strlen(buffer) + 1];strcpy_s(s.str, strlen(buffer) + 1, buffer); // 使用 strcpy_s 进行安全复制  /*char temp[String::CINLIM];is.get(temp, String::CINLIM);if (is){s = temp;}while (is && is.get() != '\n')continue;*/return is;
}String operator+(const char* c, const String& s)
{/*String temp;int size = strlen(c) + strlen(s.str) + 1;char* result = new char[size];strcpy_s(result, size, c);strcat_s(result,size, s.str);temp.len = size;temp.str = new char(size);strcpy_s(temp.str, size, result);*/String temp;temp.len = s.len + strlen(c);temp.str = new char[temp.len + 1];strcpy_s(temp.str,temp.len+1, c);strcat_s(temp.str, temp.len + 1, s.str);return temp;
}

运行结果:
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