自己写的简单String类，留作纪念

《C++ Primer Plus》第12章的编程练习2。这一章介绍类和动态内存分配，相当精彩。

编写简单的String类，并测试。

//string1.h -- fixed and augmented string class defination
#include <iostream>
using std::ostream;
using std::istream;

#ifndef STRING1_H_
#define STRING1_H_
class String
{
private:
    char *str;    // pointer to string
    int len;    // length of string
    static int num_strings;    // number of objects
    enum {CINLIM = 90};    // cin input limit
public:
    // constructor and other methods
    String(const char *s);    // constructor
    String();    // default constructor
19     String(const String &);    // copy constructor
    ~String();    // destructor
    int length() const {return len;}
    void stringlow();    // Added Stringlow
    void stringup();    // Added Stringup
    int has(const char);    // Added StringCharNum

    //overloaded operator methods
27     String& operator=(const String &);
28     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);
38     friend String operator+(const String &s1, const String &s2);

    //static function
    static int HowMany();
};
#endif

 

// string1.cpp -- String class methods
#include <cstring>                 // string.h for some
#include "string2.h"               // includes <iostream>
#include <cctype>
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 = strlen(s);          // set size
    str = new char[len + 1];       // allot storage
    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
    strcpy(str, st.str);  // copy string to new location
}

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

void String::stringlow()
{
    int i=0;
    while (str[i])
    {
        str[i]=tolower(str[i]);
        i++;
    }
}
void String::stringup()
{
    int i=0;
    while (str[i])
    {
        str[i]=toupper(str[i]);
        i++;
    }
}

int String::has(const char c)
{
    int i=0,cc=0;
    while(str[i])
    {
        if(str[i]==c)
        {
            cc++;
        }        
        i++;
    }
    return cc;
}
// 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 * s)
{
    delete [] str;
    len =strlen(s);
    str = new char[len + 1];
    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 (strcmp(st1.str, st2.str) < 0);
}

bool operator>(const String &st1, const String &st2)
{
    return st2.str < st1.str;
}

bool operator==(const String &st1, const String &st2)
{
    return (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; 
}
String operator+(const String &s1, const String &s2)//注意友元函数定义时不要friend,而且不要String::
{
    String result;
    result.len = s1.len + s2.len;
    result.str = new char[result.len+1]; 
    strcpy(result.str, s1.str);
    strcat(result.str, s2.str);
    return result;
}

 

#include <iostream>
#include "string2.h"   
int main()
{
    using std::cout;
    using std::cin;
    String s1(" and I am a C++ student.");
    String s2 = "Please enter your name: ";
    String s3;
    cout << s2;                 // overloaded << operator
    cin >> s3;                  // overloaded >> operator
    s2 = "My name is " + s3;    // overloaded =, + operators
    cout << s2 << ".\n";
    s2 = s2 + s1;
    s2.stringup();              // converts string to uppercase
    cout << "The string\n" << s2 << "\ncontains " << s2.has('A')
            << " 'A' characters in it.\n";
    s1 = "red";     // String(const char *),
    // then String & operator=(const String&)
    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();        // converts string to lowercase
        for (int i = 0; i < 3; i++)
        {
            if (ans == rgb[i])  // overloaded == operator
            {
                cout << "That's right!\n";
                success = true;
                break;
            }
        }
        if (success)
            break;
        else
            cout << "Try again!\n";
    }
    cout << "Bye\n";
    return 0;
}