自定义String

String.h

#pragma once
#include <iostream>
using namespace std;
#include <string.h>

class String
{
    friend ostream& operator<<(ostream& out, String& obj);
    friend istream& operator>>(istream& in, String& obj);
    friend bool operator <(const String& left, const String& right);
    friend bool operator >(const String& left, const String& right);
    friend bool operator ==(const String& left, const String& right);
    friend bool operator !=(const String& left, const String& right);
public:
    String();
    String(int n, char c);
    String(const char* source);
    
    String(const String& obj);
    
    String& operator=(char* s);
    String& operator=(const String& obj);

    ~String();
    char& operator[](int i);
    const char& operator[](int i)const;
    String& operator+=(const String& obj);
    String& operator+=(const char* s);
    
    char* getData() { return data; }
    int length() { return size; }
private:
    int size;
    char* data;
};

String.cpp

#include "stdafx.h"
#include "String.h"


String::String()
{
    data = new char[1];
    *data = '\0';
    size = 0;
}


String::String(int n, char c)
{
    data = new char[n + 1];
    size = n;
    char *temp = data;
    while (n--)
    {
        *temp = c;
        temp++;
    }
    temp = '\0';
}


String::String(const char* source)
{
    if (source == nullptr)
    {
        data = new char[1];
        *data = '\0';
        size = 0;
    }
    else
    {
        size = strlen(source);
        data = new char[size + 1];
        strcpy(data, source);
    }
}


String::String(const String& obj)
{
    data = new char[obj.size + 1];
    strcpy(data,obj.data);
    size = obj.size;
}


String& String::operator=(char* s)
{
    if (data != nullptr)
    {
        delete[] data;
    }
    size = strlen(s);
    data = new char[size + 1];
    strcpy(data, s);
    return *this;
}


String& String::operator=(const String& obj)
{
    if (this == &obj)
    {
        return *this;
    }
    if (data != nullptr)
    {
        delete[] data;
    }
    size = obj.size;
    data = new char[size + 1];
    strcpy(data, obj.data);
    return *this;
}

String::~String()
{
}

char& String::operator[](int i)
{
    return data[i];
}


const char& String::operator[](int i)const
{
    return data[i];
}


String& String::operator+=(const String& obj)
{
    int len = size + obj.size + 1;
    char * temp = data;
    data = new char[len];
    size = len - 1;
    strcpy(data, temp);
    strcat(data, obj.data);
    delete[] temp;
    return *this;
}


String& String::operator+=(const char* s)
{
    if (s == nullptr)
    {
        return *this;
    }
    int len = size + strlen(s) + 1;
    char* temp = data;
    data = new char[len];
    size = len - 1;
    strcpy(data, temp);
    strcat(data, s);
    delete[] temp;
    return *this;
}


ostream& operator<<(ostream& out, String& obj)
{
    for (int i = 0; i < obj.length(); ++i)
    {
        out << obj[i] << endl;
    }
    return out;
}


istream& operator>>(istream& in, String& obj)
{
    char p[1024];
    in.getline(p, 1024);
    obj = p;
    return in;
}


bool operator <(const String& left, const String& right)
{
    int i = 0;
    while (left[i] == right[i] && left[i] != 0 && right[i] != 0)
    {
        i++;
    }
    return left[i] - right[i] < 0 ? true : false;
}


bool operator >(const String& left, const String& right)
{
    int i = 0;
    while (left[i] == right[i]&&left[i] != 0 && right[i] != 0)
    {
        i++;
    }
    return left[i] - right[i]>0 ? true : false;
}


bool operator ==(const String& left, const String& right)
{
    int i = 0;
    while (left[i] == right[i] && left[i] != 0 && right[i] != 0)
    {
        i++;
    }
    return left[i] - right[i]==0 ? true : false;
}


bool operator !=(const String& left, const String& right)
{
    int i = 0;
    while (left[i] == right[i] && left[i] != 0 && right[i] != 0)
    {
        i++;
    }
    return left[i] - right[i]!=0 ? true : false;
}