【C++】模拟实现string

一、mystring

#include
#include

using namespace std;


namespace mystring
{

    class string
    {
    public:

        typedef char* iterator;

    public:

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

            strcpy(_str, str);
        }

        string(const string& s)
        {
            _capacity = s._capacity;
            _size = s._size;
            _str = new char[_capacity + 1];

            strcpy(_str, s._str);
        }

        string& operator=(const string& s)
        {

            if (this != &s)
            {
                char* tmp = new char[s._capacity + 1];
                strcpy(tmp, s._str);

                delete[] _str;
                _str = tmp;

                _size = s._size;
                _capacity = s._capacity;
            }

            return *this;
        }

        ~string()
        {
            delete[] _str;
            _size = _capacity = 0;
        }

        // iterator
        const iterator begin() const
        {
            return _str;
        }

        const iterator end() const
        {
            return _str + _size;
        }

        iterator begin()
        {
            return _str;
        }

        iterator end()
        {
            return _str + _size;
        }

        // modify
        void push_back(char c)
        {
            if (_size == _capacity)
            {
                size_t newcapacity = _capacity == 0 ? 4 : _capacity * 2;
                reserve(newcapacity);
            }
            _str[_size] = c;
            _size++;
            _str[_size] = '\0';
        }

        string& operator+=(char c)
        {
            push_back(c);
            return *this;
        }

        void append(const char* str)
        {
            int len = strlen(str);
            if (_size + len > _capacity)
            {
                reserve(_size + len);
            }

            strcpy(_str + _size, str);
            _size += len;
        }

        string& operator+=(const char* str)
        {
            append(str);
            return *this;
        }

        void clear()
        {
            _str[0] = '\0';
            _size = 0;
        }

        void swap(string& s)
        {
            char* tmp = _str;
            _str = s._str;
            s._str = tmp;

            int itmp = _size;
            _size = s._size;
            s._size = itmp;

            itmp = _capacity;
            _capacity = s._capacity;
            s._capacity = itmp;
        }

        const char* c_str()const
        {
            return _str;
        }


        // capacity

        size_t size()const
        {
            return _size;
        }

        size_t capacity()const
        {
            return _capacity;
        }

        bool empty()const
        {
            return _size == 0;
        }

        void resize(size_t n, char c = '\0')
        {
            if (n <= _size)
            {
                _str[n] = '\0';
                _size = n;
            }
            else
            {
                if (n <= _capacity)
                {
                    while (_size < n)
                    {
                        _str[_size] = c;
                        _size++;
                    }

                    _str[_size] = '\0';
                }
                else
                {
                    size_t newcapacity = _capacity == 0 ? n + 1 : _capacity + n + 1;
                    reserve(newcapacity);

                    while (_size < n)
                    {
                        _str[_size] = c;
                        _size++;
                    }

                    _str[_size] = '\0';

                }
            }
        }

        void reserve(size_t n)
        {
            if (n > _capacity)
            {
                char* tmp = new char[n + 1];

                strcpy(tmp, _str);

                delete[] _str;
                _str = tmp;
                _capacity = n;
            }
        }

        // access
        char& operator[](size_t index)
        {
            return _str[index];
        }

        const char& operator[](size_t index)const
        {
            return _str[index];
        }

        //relational operators
        bool operator<(const string& s)
        {
            return strcmp(_str, s._str) < 0;
        }

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

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

        bool operator>=(const string& s)
        {
            return *this > s || *this == s;
        }

        bool operator==(const string& s)
        {
            return strcmp(_str, s._str) == 0;
        }

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

        // 返回c在string中第一次出现的位置
        size_t find(char c, size_t pos = 0) const
        {
            for (int i = pos; i < _size; i++)
            {
                if (_str[i] == c)
                {
                    return i;
                }
            }

            return -1;
        }

        // 返回子串s在string中第一次出现的位置
        size_t find(const char* s, size_t pos = 0) const
        {
            //int len = strlen(s);
            //for (int i = 0; i <= _size - len; i++)
            //{
            //    if (strncmp(s, _str + i, len) == 0)
            //    {
            //        return i;
            //    }
            //}
            //return -1;

            const char* p = strstr(_str + pos, s);
            if (p)
            {
                return p - _str;//指针相减得到下标
            }
            else
            {
                return npos;
            }
        }

        // 在pos位置上插入字符c/字符串str
        string& insert(size_t pos, char c)
        {
            assert(pos <= _size);
            if (_size == _capacity)
            {
                size_t newcapacity = _capacity == 0 ? 4 : _capacity * 2;
                reserve(newcapacity);


            }

            size_t end = _size + 1;
            while (end > pos)
            {
                _str[end] = _str[end - 1];
                end--;
            }

            _str[pos] = c;
            _size++;

            return *this;
        }

        string& insert(size_t pos, const char* str)
        {
            assert(pos <= _size);
            int len = strlen(str);
            if (_size + len >= _capacity)
            {
                size_t newcapacity = _capacity == 0 ? len + 1 : _size + len + 1;
                reserve(newcapacity);
            }

            size_t end = _size + len;
            while (end > pos + len - 1)
            {
                _str[end] = _str[end - len];
                end--;
            }

            for (int i = 0; i < len; i++)
            {
                _str[pos + i] = str[i];
            }
            _size += len;

            return *this;
        }

        // 删除pos位置上的元素，并返回该元素的下一个位置
        string& erase(size_t pos, size_t len = npos)
        {
            assert(pos < _size);

            if (len == npos || pos + len >= _size)
            {
                _str[pos] = '\0';
                _size = pos;
            }
            else
            {
                size_t begin = pos;
                while (begin <= _size - len)
                {
                    _str[begin] = _str[begin + len];

                    begin++;
                }

                _size -= len;
            }
            return *this;
        }

    private:

        char* _str;
        size_t _capacity;
        size_t _size;
        const static size_t npos;
    };

    const size_t string::npos = -1;


    ostream& operator<<(ostream& out, const string& s)
    {
        //for (size_t i = 0; i < s.size(); i++)
        //{
        //	out << s[i];
        //}

        for (auto ch : s)
        {
            out << ch;
        }
        return out;
    }

    istream& operator>>(istream& in, string& s)
    {
        s.clear();
        char ch;
        ch = in.get();//一个字符一个字符取
        while (ch != ' ' && ch != '\n')
        {
            s += ch;
            ch = in.get();

        }

        return in;
    }
}

二、测试

 void Test1()
    {
        string s1("Hello World");

        cout << s1.c_str() << endl;

        for (int i = 0; i < s1.size(); i++)
        {
            cout << s1[i] << " ";
        }
        cout << endl;

        string::iterator it = s1.begin();

        while (it != s1.end())
        {
            cout << *it << " ";
            it++;
        }
        cout << endl;

        s1.append("hello world");
        s1.push_back('a');

        for (int i = 0; i < s1.size(); i++)
        {
            cout << s1[i] << " ";
        }
        cout << endl;

        cout << "---------------------------------------------" << endl;

    }

    void Test2()
    {
        string s1;
        s1 += '!';
        s1 += " hello world ";
        s1 += '!';
        s1.insert(0, '#');
        s1.insert(s1.size(), '*');

        cout << s1.c_str() << endl;

        s1.insert(0, "abcdefg");

        cout << s1.c_str() << endl;

        s1.insert(s1.size(), " xxxxxx");

        cout << s1.c_str() << endl;

        cout << "---------------------------------------------" << endl;

    }


    void Test3()
    {
        string s1;
        s1.insert(0, "abcdefg");

        s1.erase(6, 1);
        cout << s1.c_str() << endl;

        cout << "---------------------------------------------" << endl;

    }

    void Test4()
    {
        string s1("Hello World");
        string s2("Hello World");

        cout << s1 << " " << s2 << endl;

        cout << (s1 <= s2) << endl;
        cout << (s1 >= s2) << endl;
        cout << (s1 < s2) << endl;
        cout << (s1 < s2) << endl;

        cout << "---------------------------------------------" << endl;


    }

    void Test5()
    {
        string s1("aaabbb");
        string s2(s1);

        cout << s1 << endl;
        cout << s2 << endl;

        s1[0] = '#';

        swap(s1, s2);
        cout << s1 << endl;
        cout << s2 << endl;

        s1.resize(2);
        s2.resize(20);

        cout << s1 << endl;
        cout << s2 << endl;

        cout << "---------------------------------------------" << endl;

    }

    void Test6()
    {
        string s1 = " abcdefg";
        cout << s1.find("de") << endl;
        cout << s1.find("ccc") << endl;
        cout << s1.find("g") << endl;

        s1.resize(2);
        cout << s1 << endl;

        s1.resize(20,'x');

        cout << s1 << endl;

        cout << "---------------------------------------------" << endl;
    }