C++ Primer Plus(StringBad类的改进)

#ifndef STRING1_H#define STRING1_H#include<iostream>using std::ostream;using std::istream;class String{private:    char *str;    int len;    static int num_strings;    static const int CINLIM = 80;//cin input limitpublic:    String(const char *s);    String();    String(const String &);//copy constructor    ~String();    int length() const { return len; }    String & operator=(const String &);    String & operator=(const char*);    char & operator[] (int i);    const char & operator[] (int i) const;    friend bool operator<(const String &st, const String &st2);    friend bool operator>(const String &st, const String &st2);    friend bool operator==(const String &st, const String &st2);    friend ostream & operator<<(ostream & os, const String &st);    friend istream & operator>>(istream & is, String &st);    static int HowMany();};#endif // !STRING1_H

#include"stdafx.h"#include<cstring>#include"string1.h"using std::cin;using std::cout;int String::num_strings = 0;int String::HowMany(){    return num_strings;}String::String(const char *s){    len = std::strlen(s);    str = new char[len + 1];    std::strcpy(str, s);    num_strings++;}String::String(){    len = 4;    str = new char[1];    str[0] = '\0';    num_strings++;}String::String(const String &st){    num_strings++;    len = st.len;    str = new char[len + 1];    std::strcpy(str, st.str);}String::~String(){    --num_strings;    delete[] str;}String & String::operator=(const String &st){    if (this == &st)        return *this;    delete[] str;    len = st.len;    str = new char[len + 1];    std::strcpy(str, st.str);    return *this;}String & String::operator=(const char *s){    delete[] str;    len = std::strlen(s);    str = new char[len + 1];    std::strcpy(str, s);    return *this;}char & String::operator[](int i){    return str[i];}const char & String::operator[](int i)const//make sure thda data won't be changed{    return str[i];}bool operator<(const String &st1, const String &st2){    return (std::strcmp(st1.str, st2.str) < 0);}bool operator>(const String &st1, const String &st2){    return st2 < st1;}ostream & operator<< (ostream & os, const String & st){    os << st.str;    return os;}istream & operator >> (istream &is, String & st){    char temp[String::CINLIM];    is.get(temp, String::CINLIM);    if (is)        st = temp;    while (is && is.get() != '\n')        continue;    return is;}

// String.cpp : 定义控制台应用程序的入口点。//#include "stdafx.h"#include"string1.h"const int ArSize = 10;const int MaxLen = 81;int main(){    using std::cout;    using std::cin;    using std::endl;    String name;    cout << "<<Hi,waht's your name?\n>>";    cin >> name;    cout << name << ",please enter up to " << ArSize << " short sayings <empty line to quit>:\n";    String sayings[ArSize];    char temp[MaxLen];    int i;    for (i = 0; i < ArSize; i++)    {        cout << i + 1 << ": ";        cin.get(temp, MaxLen);        while (cin && cin.get() != '\n')            continue;        if (!cin || temp[0] == '\0')            break;        else            sayings[i] = temp;    }    int total = i;    if (total > 0)    {        cout << "Here are your sayings:\n";        for (i = 0; i < total; i++)            cout << sayings[i][0] << ": " << sayings[i] << endl;        int shortest = 0;        int first = 0;        for (i = 1; i < total; i++)        {            if (sayings[i].length() < sayings[shortest].length())                shortest = i;            if (sayings[i] < sayings[first])                first = i;        }        cout << "Shortest saying:\n" << sayings[shortest] << endl;        cout << "First alphabetically:\n" << sayings[first] << endl;        cout << "This program used " << String::HowMany() << "String objects.Bye!\n";    }    else        cout << "No input! Bye!\n";    return 0;}