C++中自己的string类实现与定义

自己的string类（有测试，C++，QT环境下，与其他环境区别不大）：

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由于许多网络博客有错误地方，自己试着写完string类的实现之后，想拿出来与大家分享，欢迎朋友们指正，评论和修改！！！一起进步，这个实现方法中存在的函数已经测试过，有可能提升的地方请大家指出！！！

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1 \ 头文件（ourstring.h）

#ifndef _ourstring_h
#define _ourstring_h

#include <iostream>
#include <cstring>
#include <cassert>

using namespace std;

static const int MAX_LENGTH = 256;

class OurString
{
    friend OurString operator+(OurString& str1, OurString& str2);
    friend void operator+=(OurString& str1, OurString& str2);
    friend ostream& operator<<(ostream& out, 
                                     const OurString& output);
    friend istream& operator>>(istream& in, OurString& input);
public:
    //constuctors and destructors;
    OurString();
    OurString(const char *str);
    OurString(const OurString& dstr);    
     //拷贝构造函数，必须是引用传参，不然来回调用了（传参也是拷贝过程）；
    ~OurString();

    //convert it to string;
    string toString();

    //get a substring;
    OurString substr(int start, int n);
    OurString substr(int start);

    //getlength;
    unsigned int length() const;

    //redifinitions;
    OurString& operator=(const OurString& str);

    bool operator==(const OurString& str);
    bool operator!=(const OurString& str);
    bool operator>=(const OurString& str);
    bool operator<=(const OurString& str);
    bool operator>(const OurString& str);
    bool operator<(const OurString& str);

    char operator[](int index) const;

private:
    bool isinbound(int index) const;
    char *ptr = NULL;
    unsigned int len;
};

OurString operator+(OurString& str1, OurString& str2);
void operator+=(OurString& str1, OurString& str2);
ostream& operator<<(ostream& out, const OurString& output);
istream& operator>>(istream& in, const OurString& input);

#endif

2 \ 实现文件（ourstring.cpp）

#include "ourstring.h"
#include "strlib.h"
using namespace std;

//----------------FRIEND-----------------//
OurString operator+(OurString& str1, OurString& str2)
{
    if(str1.len + str2.len > MAX_LENGTH)
    {
        cout << "Sorry, the string is too large! We can't add them!";
        return str1;
    }
    OurString _Added = str1;
    _Added.ptr = strcat(_Added.ptr, str2.ptr);
    _Added.len = str1.len + str2.len;
    return _Added;
}
void operator+=(OurString& str1, OurString& str2)
{
    if(str1.len + str2.len > MAX_LENGTH)
        cout << "Sorry, the string is too large! We can't add them!";
    strcat(str1.ptr, str2.ptr);
    str1.len = str1.len + str2.len;
}
ostream& operator<<(ostream& out, const OurString& output)
{
    out << output.ptr;
    return out;
}
istream& operator>>(istream& in, OurString& input)
{
    in >> input.ptr;
    input.len = strlen(input.ptr);
    return in;
    //应有一个清空函数（if超过了,清空in），暂时没找到；
}

//------------------constrectors and destructors-------------------//
OurString::OurString()
{
    ptr = new char[1];
    ptr[0] = '\0';
    assert(ptr != 0);
    len = 0;
}

OurString::OurString(const char *str)
{
    if(strlen(str) > MAX_LENGTH)
    {
        cout << "Sorry, the string is too large!";
        return;
    }
    if(ptr != NULL)
    {
        delete [] ptr;
    }
    ptr = new char[strlen(str) + 1];
    assert(ptr != 0);
    ptr = strcpy(ptr, str);
    len = strlen(str);
}

OurString::OurString(const OurString& dstr)
{
    if(ptr != NULL)
    {
        delete [] ptr;
    }
    ptr = new char[dstr.len + 1];
    assert(ptr != 0);
    ptr = strcpy(ptr, dstr.ptr);
    len = dstr.len;
}

OurString::~OurString()
{
    if(ptr != NULL)
        delete [] ptr;
}
//-----------------others--------------//
string OurString::toString()
{
    string Convertion = ptr;
    return Convertion;
}

OurString OurString::substr(int start)
{
    OurString substring;
    if( !isinbound(start) )
    {
        cout << "It is out of the bound!!!";
        return substr(len, 1);
    }
    substring.ptr = new char[len + 1 - start];
    for(int i = 0; i <= len - start; i++)
    {
        substring.ptr[i] = ptr[start + i];
    }
    substring.len = len - start;
    return substring;
}

OurString OurString::substr(int start, int n)
{
    if( !isinbound(start + n - 1) )
    {
        cout << "It is out of the bound!!!";
        return substr(len, 1);
    }
    else
    {
        OurString substring;
        substring.ptr = new char[n + 1];
        int i = 0;
        for(; i < n; i++)
            substring.ptr[i] = ptr[start + i];
        substring.ptr[i] = '\0';
        substring.len = n;
        return substring;
    }
}

unsigned int OurString::length() const
{
    return len;
}

bool OurString::operator==(const OurString& str)
{
    int IF = strcmp(ptr, str.ptr);
    if(IF == 0)
        return true;
    else
        return false;
}

bool OurString::operator!=(const OurString& str)
{
    int IF = strcmp(ptr, str.ptr);
    if(IF == 0)
        return false;
    else
        return true;
}

bool OurString::operator>(const OurString& str)
{
    int IF = strcmp(ptr, str.ptr);
    if(IF > 0)
        return true;
    else
        return false;
}

bool OurString::operator>=(const OurString& str)
{
    int IF = strcmp(ptr, str.ptr);
    if(IF >= 0)
        return true;
    else
        return false;
}

bool OurString::operator<(const OurString& str)
{
    int IF = strcmp(ptr, str.ptr);
    if(IF < 0)
        return true;
    else
        return false;
}

bool OurString::operator<=(const OurString& str)
{
    int IF = strcmp(ptr, str.ptr);
    if(IF <= 0)
        return true;
    else
        return false;
}

char OurString::operator[](int index) const
{
    if(!isinbound(index))
    {
        cout << "The index is not in bound of the string!!!";
        return '\0';
    }
    return ptr[index];
}

OurString& OurString::operator=(const OurString& str)
{
    if (this == &str) return *this;
    if(ptr != NULL)
    {
        delete [] ptr;
    }
    ptr = new char[str.len + 1];
    assert(ptr != 0);
    ptr = strcpy(ptr, str.ptr);
    len = str.len;
    return *this;
}

bool OurString::isinbound(int index) const
{
    if(index <= len && index >= 0)
        return true;
    else
        return false;
}

3 \ 主函数（测试）

#include <iostream>
#include <cstring>
#include "console.h"
#include "ourstring.h"

using namespace std;

/*
 * Main program
 */

int main()
{
    cout<<"Let's test OurString!"<< endl;
    OurString s0;
    OurString s1("qwe");
    OurString s2 = "123456";
    OurString s3;
    s3 = s1 + s2;
    cout << "s0 = " << s0 << "yes!" << endl;
    cout << "s1 = " << s1 << endl;
    cout << "s2 = " << s2 << endl;
    cout << (s1 == s2) << "  " << (s1 < s2) << "  " 
    << (s1 > s2) << "  " << (s1 <= s2) << "  "
    << (s1 >= s2) << "  " << (s1 != s2) << endl;
    cout << "s3 = " << s3 << endl;
    s3 += s2;
    cout << "s3 = " << s3 << endl;
    OurString s4;
    cout << "Please input s4: ";
    cin >> s4;
    cout << "s4 = " << s4 << endl;
    string str = s4.toString();
    cout << "String of s4 = " << s4 << endl;
    cout << s4.substr(4, 5) << endl;
    cout << s4.substr(4) << endl;
    cout << s4.length() << endl;
    cout << s4[5] << endl;
    s4 = s1;
    cout << s4 << endl;
    return 0;
}

这是“in the bound”的情况。

这是“out of bound”的情况。