C++实现String

浅拷贝

深拷贝

总结：浅拷贝只是对指针的拷贝，拷贝后两个指针指向同一个内存空间，深拷贝不但对指针进行拷贝，而且对指针指向的内容进行拷贝，经深拷贝后的指针是指向两个不同地址的指针。

String.h

#pragma once

#include <iostream>
#include <stdio.h>
#include <string.h>

using namespace std;

class String
{
    friend ostream& operator<<(ostream& _cout, const String& s);
    friend istream& operator>>(istream& _cin, String& s);

public:
    String(const char* str = "")
        :_str(new char[strlen(str) + 1])
        , _size(strlen(str))
        , _capacity(strlen(str) + 1)
    {
        strcpy(_str, str);
    }

    // String s2(s1) 
    String(const String& s)
        :_str(new char[strlen(s._str) + 1])
        , _size(strlen(s._str))
        , _capacity(strlen(s._str) + 1)
    {
        _str = s._str;
        _size = s._size;
        _capacity = s._capacity;
    }

    ~String()
    {
        if (_str)
        {
            delete[] _str;
            _str = NULL;
        }
    }

    const char* c_str()
    {
        return _str;
    }

    //增删查改
    void Expand(size_t n);
    void PushBack(char ch);
    void PushBack(const char* str);
    void PopBack();
    void Insert(size_t pos, char ch);
    void Insert(size_t pos, const char* str);
    void Erase(size_t pos, size_t n);

    size_t Find(char ch) const;
    size_t Find(const char* str) const; 

    void Swap(String& s);
    // s1 = s2 
    String& operator=(String s);
    // s1 + 'a' 
    String operator+(char ch);
    String& operator+=(char ch);
    String operator+(const char* str);
    String& operator+=(const char* str);

    bool operator<(const String& s) const;
    bool operator<=(const String& s) const;
    bool operator>(const String& s) const;
    bool operator>=(const String& s) const;
    bool operator==(const String& s) const;
    bool operator!=(const String& s) const;

private:
    char* _str;
    size_t _size;
    size_t _capacity;
};

ostream& operator<<(ostream& _cout, const String& s)
{
    _cout << "str: " <<s._str << "  size:" << s._size << "  capacity:" << s._capacity << endl;
    return _cout;
}

istream& operator>>(istream& _cin, String& s)
{
    _cin >> s._str;
    return _cin;
}

String.c

#define _CRT_SECURE_NO_WARNINGS 1

#include "String.h"
#include <windows.h>
#include <assert.h>

void String::Expand(size_t n)    //扩容
{
    if (n > _capacity)
    {
        _str = (char*)realloc(_str, n + 1);
        _capacity = n + 1;
    }
}

//增删查改
void String::PushBack(char ch)
{
    if (_size >= _capacity - 1)
    {
        Expand(_capacity * 2);
    }
    _str[_size] = ch;
    _size++;
    _str[_size] = '\0';    //最后加上'\0'
}

void String::PushBack(const char* str)
{
    size_t len = strlen(str);
    if (len + _size >= _capacity - 1)
    {
        Expand(len + _size);
    }
    strcpy(_str + _size, str);
    _size = strlen(_str);
}

void String::PopBack()
{
    if (_size > 0)
    {
        _str[_size - 1] = _str[_size];    //将'\0'前移
        --_size;
    }
}

void String::Insert(size_t pos, char ch)
{
    if (_size >= _capacity)
    {
        Expand(_capacity * 2);
    }
    size_t end = _size;
    while (end >= pos)
    {
        _str[end + 1] = _str[end];
        --end;
    }
    _str[pos] = ch;
    ++_size;
}

void String::Insert(size_t pos, const char* str)
{
    size_t len = strlen(str);
    size_t tmp = len;
    if (_size + len > _capacity)
    {
        Expand(_size + len);
    }
    size_t end = _size;
    while (end >= pos)
    {
        _str[end + len] = _str[end];
        --end;
    }
    while (len-- > 0)
    {
        _str[pos++] = *str++;
    }
    _size += tmp;
}

void String::Erase(size_t pos, size_t n)
{
    if (pos + n >= _size - 1)
    {
        _str[pos] = '\0';
        _size = pos;
    }
    else
    {
        strcpy(_str + pos, _str + pos + n);     //相当于直接将'\0'拷到pos处
        _size -= n;
    }
}

size_t String::Find(char ch) const
{
    for (size_t i = 0; i < _size; ++i)
    {
        if (_str[i] == ch)
        {
            return i;
        }
    }
    return -1;
}

size_t String::Find(const char* str) const
{
    assert(str);
    char* start = (char*)_str;
    char* substart = (char*)str;
    char* ret = (char*)_str;
    while (*ret)
    {
        start = ret;
        if (*start && *substart && (*start == *substart))
        {
            ++start;
            ++substart;
        }
        if (*substart == '\0')
        {
            return 1;
        }
        substart = (char*)str;
        ret++;
    }
    return -1;
}

// s1.Swap(s2); 
void String::Swap(String& s)
{
    if (*this != s)
    {
        swap(_str, s._str);
        swap(_size, s._size);
        swap(_capacity, s._capacity);
    }
}

// s1 = s2 (现代写法)
String& String::operator=(String s)
{
    if (this != &s)
    {
        _size = s._size;
        _capacity = s._capacity;
        swap(_str, s._str);
    }
    return *this;
}

//// s1 = s2 (传统写法)
//String& String::operator=(String s)
//{
//  if (this != &s)
//  {
//      int len = strlen(s._str);
//      char* tmp = new char[len + 1];
//      strcpy(tmp, s._str);
//      _str = NULL;
//      _str = tmp;
//  }
//  return *this;
//

String String::operator+(const char* str)
{
    String *s = new String;
    s->_size = _size + strlen(str);
    s->_capacity = _capacity + strlen(str);
    s->_str = new char[s->_size + 1];
    strcpy(s->_str, _str);
    strcat(s->_str, str);
    return *s;
}

String& String::operator+=(const char* str)
{
    _size += strlen(str);
    _capacity += strlen(str);
    char *s = new char[_size + 1];
    strcpy(s, _str);
    strcat(s, str);
    delete[] _str;
    _str = s;
    return *this;
}

bool String::operator<(const String& s) const
{
    size_t i = 0;
    for (; i < _size && i < s._size; ++i)
    {
        if (_str[i] < s._str[i])
        {
            return true;
        }
        else
        {
            return false;
        }
    }
    if (i == _size)
    {
        return true;
    }
    else
    {
        return false;
    }
}

bool String::operator<=(const String& s) const
{
    return *this < s || *this == s;
}

bool String::operator>(const String& s) const
{
    return !(*this <= s);
}

bool String::operator>=(const String& s) const
{
    return !(*this < s);
}

bool String::operator==(const String& s) const
{
    size_t i = 0;
    for (; i < _size && i < s._size; ++i)
    {
        if (_str[i] != s._str[i])
        {
            return false;
        }
    }
    if (i == _size && i == s._size)
    {
        return true;
    }
    return false;
}

bool String::operator!=(const String& s) const
{
    return !(*this == s);
}

int main()
{
    //String s1("hello");
    //String s2(s1);
    //String s3("world!");
    //cout << s1;
    //cout << s2;
    //cout << s3;

    //String s4("HELLO");
    //s3 = s4;
    //cout << s3;
    //cout << s4;

    //printf("s1 == s2:%d", s1==s2);
    //printf("\n");
    //printf("s3 > s1:%d", s3>s1);
    //printf("\n");

    //s1.Swap(s3);
    //cout << s1;
    //cout << s3;

    //printf("s1 < s2:%d", s1< s2);
    //printf("\n");

    //String s1("hello");
    ////s1 += "world";
    ////cout << s1;
    //String s2;
    //s2 = s1 + " world";
    //cout << s1;
    //cout << s2;

    String s1("hello");
    s1.PushBack('w');
    s1.PushBack('o');
    s1.PushBack('r');
    s1.PushBack('l');
    s1.PushBack('d');
    cout << s1;
    s1.PushBack(" hahaha");
    cout << s1;
    s1.PopBack();
    s1.PopBack();
    s1.PopBack();
    s1.PopBack();
    cout << s1;
    s1.Insert(5, ' ');
    s1.Insert(11, '!');
    cout << s1;
    s1.Insert(13, "everyone ");
    cout << s1;
    s1.Erase(13, 9);
    cout << s1;
    size_t tmp = s1.Find('o');
    printf("%lu\n", tmp);
    tmp = s1.Find("hehe");
    printf("%lu\n", tmp);
    system("pause");
    return 0;
}