string类中各成员函数的实现

一、string类的定义

class MyString
{
public:
    MyString();
    MyString(char *sz);
    MyString(const MyString &other);
    MyString& operator=(const MyString &rhs);
    MyString& operator=(const char *str);
    char& operator[](unsigned int index);
    const char& operator[](unsigned int index) const;
    friend MyString operator+(const MyString &s1, const MyString &s2);
    friend ostream& operator<<(ostream &os, const MyString &str);
    friend istream& operator>>(istream &is, MyString &str);
    bool isEmpty();

    ~MyString();

    int assign(const char *obj);
    void display() const;
    int replace(const char *from, const char *to);
    int append(const char *obj);
    unsigned int getSize() const;

private:
    char *m_data;
    unsigned int m_len;
};

二、类成员函数的实现

MyString::MyString()
{
    m_data = NULL;
    m_len = 0;
}

MyString::MyString(char *sz)
{
    m_len = strlen(sz);
    m_data = new char[m_len + 1];
    strcpy(m_data, sz);
}

MyString::MyString(const MyString &other)
{
    m_len = other.m_len;
    m_data = new char[m_len];
    strcpy(m_data, other.m_data);
}

MyString& MyString::operator=(const MyString &rhs)
{
    if(this == &rhs)
    {
        return *this;
    }

    if(m_data != NULL)
    {
        delete []m_data;
    }
    m_len = rhs.m_len;
    m_data = new char[m_len + 1];
    strcpy(m_data, rhs.m_data);

    return *this;
}

MyString& MyString::operator=(const char *str)
{
    if(m_data != NULL)
    {
        delete []m_data;
    }
    m_len = strlen(str);
    m_data = new char[m_len + 1];
    strcpy(m_data, str);

    return *this;
}

char& MyString::operator[](unsigned int index)
{
    cout << "char& MyString::operator[](unsigned int index)" << endl;
    return *(m_data + index); //m_data[index]
}

const char& MyString::operator[](unsigned int index) const
{
    cout << "const char& MyString::operator[](unsigned int index) const" << endl;
    return *(m_data + index);
}
bool MyString::isEmpty()
{
   return m_len == 0; //m_len
}

MyString::~MyString()
{
    if(m_data != NULL)
    {
        delete []m_data;
    }
}

int MyString::assign(const char *obj)
{
    if(m_data != NULL)
    {
        delete []m_data;
    }

    m_len = strlen(obj);
    m_data = new char[m_len + 1];
    strcpy(m_data, obj);
}

void MyString::display() const
{
    if(m_data == NULL)
    {
        cout << "str is NULL" <<endl;
    }

    cout << m_data << endl;
}

int MyString::replace(const char *from, const char *to)
{
    char *q,*tmp,*cur;
    tmp = strstr(m_data, from);
    if(strlen(from) < strlen(to) || tmp == NULL)
    {
        return -1;
    }
    char *p = new char[m_len];
    q = p;
    cur = m_data;
    for(int i = 0; i < (tmp - m_data); i++)
    {
        *q = *cur;
        q++;
        cur++;
    }
    *q = '\0';
    strcat(p, to);

    tmp = tmp + strlen(from);
    strcat(p,tmp);

    m_data = p;

    return 0;
}

int MyString::append(const char *obj)
{
    m_len += strlen(obj);
    char *tmp = new char[m_len + 1];
    char *p = tmp, *q = m_data;
    while(*q != '\0')
    {
        *p = *q;
        p++;
        q++;
    }
    if(m_data != NULL)
    {
        delete []m_data;
        m_data = NULL;
    }
    strcat(tmp,obj);

    m_data = tmp;
    return 0;
}

unsigned int MyString::getSize() const
{
    return m_len;
}

三、友元函数的实现

MyString operator+(const MyString &s1, const MyString &s2)
{
    int len = strlen(s1.m_data) + strlen(s2.m_data);
    MyString tmp;
    tmp.m_data = new char[len + 1];
    tmp.m_len = len;
    strcat(tmp.m_data,s1.m_data);
    strcat(tmp.m_data,s2.m_data);

    return tmp;
}

ostream& operator<<(ostream &os, const MyString &str)
{
    os << str.m_data;

    return os;
}

istream& operator>>(istream &is, MyString &str)
{
    if(str.m_data != NULL)
    {
        delete []str.m_data;
        str.m_data = NULL;
        str.m_len = 0;
    }

    char tmp[1024] = {0};
    cin >> tmp;
    str.m_len = strlen(tmp);
    str.m_data = new char[str.m_len + 1];

    strcpy(str.m_data,tmp);

    return is;
}