String的增删查改的实现

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String类主要模拟实现string(库)中字符串的增删查改操作。有插入一个字符，插入一个字符串，删除一个特定位置的字符，删除特定位置特定的字符串，头插，头删，尾插，尾删，可以复用Insert()和Erase()函数。字符串比较，字符相同则同时向后走，当字符串相同，或有不同的字符时返回相应的结果。具体操作如下：

#pragma warning(disable:4996)//禁止报strcpy的错误#include<iostream>#include<cassert>using namespace std;class String{public:    String(const char* str ="")    {        size_t len = strlen(str);        _str = new char[len+1];        strcpy(_str,str);        _size = len;        _capacity = len;    }    //s1(s2)    String(const String& s)        :_str(NULL)        ,_size(0)        ,_capacity(0)    {       String tmp(s._str);       Swap(tmp);    }    //d1=d2    String& operator=(String s)//现代写法    {       this->Swap(s);       return *this;    }    void Swap(String& s)    {        swap(_str, s._str);        swap(_size, s._size);        swap(_capacity, s._capacity);    }    ~String()    {       if(_str)       {           delete[] _str;           _str = NULL;           _size = _capacity = 0;       }    }    char* GetStr()    {        return _str;    }    size_t Size()    {       return _size;    }    size_t Capacity()    {       return _capacity;    }    char& operator[](size_t pos)    {        assert(pos < _size);        return _str[pos];    }    void Expand(size_t n)    {       assert(n > _capacity);       _str = (char*)realloc(_str,n+1);       _capacity = n;    }    void PushBack(char ch)//尾插一个字符    {       if(_size == _capacity)       {           Expand(_capacity*2);       }       _str[_size] = ch;       ++_size;       _str[_size] = '\0';    }    void PushBack(const char* str)//尾插一个字符串    {        size_t len = strlen(str);        if(_size+len > _capacity)        {            Expand(_size+len);        }        strcpy(_str+_size,str);    }    void PopBack()    {        if(_size)        {            --_size;            _str[_size] = '\0';        }    }    void PushFront(char ch)    {        Insert(0,ch);    }    void PushFront(const char* str)    {        Insert(0,str);    }    void PopFront()    {        if(_str)        {               strcpy(_str,_str+1);            --_size;        }    }

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    void Insert(size_t pos, char ch)//在pos前面插入一个字符    {        if(_size == _capacity)            Expand(_capacity*2);        //挪动数据        int end = _size;        while(end >= (int)pos)        {            _str[end+1] = _str[end];            --end;        }        _str[pos] = ch;        ++_size;    }    void Insert(size_t pos, const char* str)//在pos前面插入一个字符串    {        size_t len = strlen(str);        if(_size+len > _capacity)            Expand(_size+len);        int end = _size;        while(end >= (int)pos)        {            _str[end+len] = _str[end];            --end;        }        while(*str)            _str[pos++] = *str++;        _size = _size + len;    }    void Erase(size_t pos, size_t count)    {        if(pos+count >= _size-1)        {            _str[pos] = '\0';            _size = pos;        }        else        {            strcpy(_str+pos, _str+pos+count);            //把pos+count之后的内容拷贝到pos后            _size -= count;        }    }

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    int Find(char ch) const    {        for(size_t i=0; i<_size; ++i)        {            if(_str[i] == ch)                return i;        }        return -1;    }    int Find(const char* str) const    {        assert(str);        const char* srcStr = _str;        const char* subStr = str;        size_t subLen = strlen(str);        size_t srcIndex = 0;        size_t subIndex = 0;        while(srcIndex < _size)        {            size_t matchIndex = srcIndex;            while(srcStr[matchIndex] == subStr[subIndex])            {                ++matchIndex;                ++subIndex;                if(subIndex == subLen)                    return srcIndex;            }            subIndex = 0;            srcIndex++;        }    return -1;    }    bool operator<(const String& s)    {        size_t i=0;        for( ;i<_size && i<s._size; ++i)        {            if(_str[i] < s._str[i])                return true;            else if(_str[i] > s._str[i])                return false;        }        if(i == _size && i<s._size)//i是已经for循环过的值            return true;        else            return false;    }    inline bool operator<=(const String& s)     {        return *this<s || *this == s;    }    inline bool operator>(const String& s)     {        return !(*this<=s);    }    bool operator>=(const String& s)     {        return !(*this<=s) || *this == s;    }    bool operator==(const String& s)     {        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;        else            return false;    }    bool operator!=(const String& s)     {        return !(*this == s);    }private:    char* _str;    size_t _size;//字符个数    size_t _capacity;//容量空间};

测试用例：

#include"String.h"void TestString1(){    String s1("hello");    String s2(s1);    //cout<<s1.GetStr()<<endl;    //cout<<s2.GetStr()<<endl;    s1.PushBack(' ');    s1.PushBack('C');    s1.PushBack('h');    s1.PushBack('i');    s1.PushBack('n');    s1.PushBack('a');    cout<<s1.GetStr()<<endl;    /*s2.PushBack(" China");    cout<<s2.GetStr()<<endl;*/    s1.PushFront(' ');    s1.PushFront('m');    cout<<s1.GetStr()<<endl;    /*s2.PopBack();    s2.PopBack();    s2.PopBack();    s2.PopBack();    s2.PopBack();    s2.PopBack();*/   // cout<<s2.GetStr()<<endl;    s2.PopFront();    s2.PopFront();    s2.PopFront();    s2.PopFront();    s2.PopFront();    s2.PopFront();    cout<<s2.GetStr()<<endl;    String s3("world");    s3.Insert(0,"hello ");    s3.Insert(6,'m');    cout<<s3.GetStr()<<endl;    //s3.Erase(7,2);    //cout<<s3.GetStr()<<endl;    cout<<"Pos"<<s3.Find('w')<<endl;    cout<<"Pos"<<s3.Find("wor")<<endl;}void TestString2(){    String s1("computer");    String s2("compare");    String s3("computerly");    String s4("computer");    bool ret;    //ret = s1<s2;    //cout<<"s1<s2 ? "<<ret<<endl;    //ret = s1<s3;    //cout<<"s1<s3 ? "<<ret<<endl;    /*ret = s1>s2;    cout<<"s1 >s42? "<<ret<<endl;*/    /*ret = s1>=s2;    cout<<"s1 >= s2 ? "<<ret<<endl;*/    ret = s1<=s2;    cout<<"s1 <= s2 ? "<<ret<<endl;}int main(){    //TestString1();    TestString2();    return 0;}

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