C++实现String类

// string1.h -- fixed and augmented string class definition

#ifndef STRING1_H_
#define STRING1_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 &st, const String &st2);
    friend bool operator>(const String &st1, 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 function
    static int HowMany();
};

#endif

// string1.cpp -- String class methods
#include <cstring>                 // string.h for some
#include "string1.h"               // includes <iostream>
using std::cin;
using std::cout;

// initializing static class member

int String::num_strings = 0;

// static method
int String::HowMany()
{
    return num_strings;
}

// class methods
String::String(const char * s)     // construct String from C string
{
    len = std::strlen(s);          // set size
    str = new char[len + 1];       // allot storage
    std::strcpy(str, s);           // initialize pointer
    num_strings++;                 // set object count
}

String::String()                   // default constructor
{
    len = 4;
    str = new char[1];
    str[0] = '\0';                 // default string
    num_strings++;
}

String::String(const String & st)
{
    num_strings++;             // handle static member update
    len = st.len;              // same length
    str = new char [len + 1];  // allot space
    std::strcpy(str, st.str);  // copy string to new location
}

String::~String()                     // necessary destructor
{
    --num_strings;                    // required
    delete [] str;                    // required
}

// 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];
    std::strcpy(str, st.str);
    return *this;
}

    // assign a C string to a String
String & String::operator=(const char * s)
{
    delete [] str;
    len = std::strlen(s);
    str = new char[len + 1];
    std::strcpy(str, s);
    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 (std::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 (std::strcmp(st1.str, st2.str) == 0);
}

    // simple String output
ostream & operator<<(ostream & os, const String & st)
{
    os << st.str;
    return os; 
}

    // quick and dirty String input
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; 
}

// sayings1.cpp -- using expanded String class
// compile with string1.cpp
#include <iostream>
#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, what's your name?\n>> ";
    cin >> name;

    cout << name << ", please enter up to " << ArSize
         << " short sayings <empty line to quit>:\n";
    String sayings[ArSize];     // array of objects
    char temp[MaxLen];          // temporary string storage
    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')    // empty line?
            break;              // i not incremented
        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";
// keep window open 
/*    if (!cin)
        cin.clear();
    while (cin.get() != '\n')
        continue; */ 
   return 0; 
}