c++---实现mystring

1.string.h

//string.h
#ifndef STRING_H_
#define STRING_H_
#include <iostream>
using std::ostream;
using std::istream;
class String
{
private:
    char *str; //pointer to string
    int len; //length of string
    static int num_strings; //number of objects
    static const int CINLIM = 80; //cin input limit
public:
    //constructors and other methods
    String(const char *s); //constructor
    String();//default constructor
    String(const String &);//copy constructor
    ~String(); //destructor
    int length() const {return len;}
    //overloaded operator methods
    String & operator=(const String &);
    String & operator=(const char *);
    char & operator[](int i);
    const char & operator[](int i) const;
    //overloaded operator friends
    friend bool operator<(const String &st1, const String &st2);
    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 &st);
    friend istream & operator>>(istream &is, String &st);
    //static function
    static int HowMany();
    };
#endif // STRING_H_

           

2.string.cpp

//string.cpp--String class methods
#include <cstring>
#include "string.h"
using namespace std;
//initializing static class member
int String::num_strings = 0;
//static method
int String::HowMany()
{
    return num_strings;
}
//constructors and other methods
String::String(const char *s) //constructor String from C string
{
    len = strlen(s); //set size
    str = new char[len + 1]; //allocate storage
    strcpy(str, s);
    num_strings++; //set object count
}
String::String()//default constructor
{
    len = 0;
    str = new char[1];
    str[0] = '\0';
    num_strings++;
}
String::String(const String &st) //copy constructor
{
    num_strings++;
    len = st.len;
    str = new char[len + 1];
    strcpy(str, st.str);
}

String::~String()
{
    --num_strings;
    delete [] str;
}
//overloaded operator methods
//assign a String to a String
String & String::operator=(const String &st)
{
    if (this == &st)
        return *this;
    delete [] str;
    len = st.len;
    str = new char[len + 1];
    strcpy(str, st.str);
    return *this;
}

//assign a C string to a String
String & String::operator=(const char *st)
{
    delete [] str;
    len = strlen(st);
    str = new char[len + 1];
    strcpy(str, st);
    return *this;

}

//read-write char access for non-const String
char & String::operator[](int i)
{
    return str[i];
}

//read-only char access for const string
const char & String::operator[](int i) const
{
    return str[i];
}

//overloaded operator friends
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 operator==(const String &st1, const String &st2)
{
   return (strcmp(st1.str, st2.str) == 0);
}

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;
}
           

3.using_string.cpp

//using_string.cpp
#include <iostream>
#include "string.h"
using namespace std;

const int ArSize = 10;
const int MaxLen = 81;

int main()
{
    String name;
    cout << "Hi, what'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 = 0;

    for (; i < ArSize; i++)
    {
        cout << i + 1 << ":";
        cin.get(temp, MaxLen);

        while (cin && cin.get() != '\n')
            continue;
        if (!cin || temp[0] == '\0') //empty line?
            break;
        else
            sayings[i] = temp; //overloaded assignment
    }

    int total = i; //total # of lines read

    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;
}
           

运行结果：

Hi, what's your name?
>>Misty Gutz
Misty Gutz, please enter up to 10 short sayings <empty line to quit>:
1:a fool and his money are soon parted
2:penny wise, pound foolish
3:the love of money is the root of much evil
4:out of sight, out of mind
5:absence makes the heart grow fonder
6:absinthe makes the hart grow fonder
7:
Here are your sayings:
a: a fool and his money are soon parted
p: penny wise, pound foolish
t: the love of money is the root of much evil
o: out of sight, out of mind
a: absence makes the heart grow fonder
a: absinthe makes the hart grow fonder
shortest saying:
penny wise, pound foolish
First alphabetically:
a fool and his money are soon parted
This program used 11 String objects. Bye.