实现简单的string类

摘要

实现了一个string类，包括基本的构造、赋值、判断、大小写等。

String API

Constructors

string();
string(const char& ch);
string(const char* str);
string(const string& str);

Informational Methods

unsigned Length() const;
int Index(char c) const;

Case Methods

void UpCase(unsigned first, unsigned last);
void LowCase(unsigned first, unsigned last);

Stream Operators

friend std::ostream& operator<<(std::ostream& os, const string& str);
friend std::istream& operator>>(std::istream& is, string& str);

Accessor Operators

const char& operator[](unsigned i) const;
char& operator[](unsigned i);

Assignment Operators

String&  operator= (const String&)
String& operator+= (const String&)

String Concatenation

friend string operator+(const string& lhs, const string& rhs);
friend string operator+(const string& lhs, const char* rhs);
friend string operator+(const char* lhs, const string& rhs);

Logical Operators

friend bool operator==(const string& lhs, const string& rhs);
friend bool operator!=(const string& lhs, const string& rhs);
friend bool operator<(const string& lhs, const string& rhs);
friend bool operator>(const string& lhs, const string& rhs);

#include "string.h"

using namespace vlyf;

inline
vlyf::string::string()
{
    length = 0;
    data = new char[0];
}

inline
string::string(const char* str)
{
    if (str)
    {
        unsigned n = 0;
        while (str[n] != '\0') n++;
        data = new char[n];
        length = n;
        for (unsigned i = 0; i < n; i++)
        {
            data[i] = str[i];
        }
    }
    else
    {
        length = 0;
        data = new char[0];
    }
}

inline
string::string(const string& str)
{
    unsigned len = str.Length();
    length = len;
    data = new char[len];
    for (unsigned i = 0; i < len; i++)
    {
        data[i] = str[i];
    }
}

inline
string::~string()
{
    delete[]data;
}

inline
unsigned string::Length() const
{
    return length;
}

int string::Index(char c) const
{
    for (unsigned i = 0; i < Length(); i++)
    {
        if (c == data[i]) return i;
    }
    return -1;
}

inline
void string::UpCase(unsigned first, unsigned last)
{
    while (first++ < last)
    {
        if ('a' <= data[first] && data[first] <= 'z')
            data[first] -= ('a' - 'A');
    }
}

inline
void string::LowCase(unsigned first, unsigned last)
{
    while (first++ < last)
    {
        if ('A' <= data[first] && data[first] <= 'Z')
            data[first] += ('a' - 'A');
    }
}

const char& vlyf::string::operator[](unsigned i) const
{
    return data[i];
}

char& vlyf::string::operator[](unsigned i)
{
    return data[i];
}

string& vlyf::string::operator=(const char* s)
{
    char* temp = data;                  //保存原本数据，确保异常安全性
    unsigned n = 0;
    while (s[n] != '\0')
        n++;
    length = n;
    data = new char[n];
    for (unsigned i = 0; i < n; i++)
        data[i] = s[i];
    delete[] temp;
    return *this;
}

inline
string& vlyf::string::operator=(const string& str)
{
    if (this == &str) return *this;
    char* temp = str.data;              //保存原本数据，确保异常安全性

    unsigned len = str.Length();
    data = new char[len];
    for (unsigned i = 0; i < len; i++)
        data[i] = str[i];
    length = len;
    delete[] temp;
    return *this;
}

inline
string& string::operator+=(const string& str)
{
    unsigned len = length + str.Length();
    char* ss = new char[len];
    for (unsigned i = 0; i < Length(); i++)
        ss[i] = data[i];
    for (unsigned i = 0; i < str.Length(); i++)
        ss[i + length] = str[i];
    delete[]data;
    data = ss;
    length = len;
    return *this;
}

std::ostream& vlyf::operator<<(std::ostream& os, const string& str)
{
    if (str.Length() > 0)
    {
        for (unsigned i = 0; i < str.Length(); i++)
            os << str[i];
    }
    else
    {
        os << "";
    }
    return os;
}

std::istream& vlyf::operator>>(std::istream& is,string& str)
{
    char* ss = new char[1000];
    is >> ss;
    str = string(ss);
    return is;
}

string vlyf::operator+(const string& lhs, const string& rhs)
{
    return string(lhs) += rhs;
}

string vlyf::operator+(const string& lhs, const char* rhs)
{
    return string(lhs) += string(rhs);
}

string vlyf::operator+(const char* lhs, const string& rhs)
{
    return string(lhs) += string(rhs);
}

bool vlyf::operator==(const string& lhs, const string& rhs)
{
    if (lhs.Length() != rhs.Length())
        return false;
    unsigned n = 0;
    unsigned len = lhs.Length();
    while (lhs[n] == rhs[n] && len != n)
        n++;
    return n == len;
}

bool vlyf::operator!=(const string& lhs, const string& rhs)
{
    if (lhs.Length() != rhs.Length())
        return true;
    unsigned n = 0;
    unsigned len = lhs.Length();
    while (lhs[n] == rhs[n] && len != n)
        n++;
    return n != len;
}

bool vlyf::operator<(const string& lhs, const string& rhs)
{
    unsigned min = (lhs.Length() < rhs.Length()) ? lhs.Length() : rhs.Length();
    unsigned n = 0;
    while (lhs[n] == rhs[n] && n != min)
        n++;
    if (n == min) return lhs.Length() < rhs.Length();
    else
    {
        if (lhs[n] < rhs[n])
            return lhs.Length() < rhs.Length();
        else
            return lhs.Length() > rhs.Length();
    }
}

bool vlyf::operator>(const string& lhs, const string& rhs)
{
    return lhs < rhs;
}

int main()
{
    string s1 = "123";
    std::cout << "s1:" << s1 << "       length: " << s1.Length() << std::endl;

    string s2("456");
    std::cout << "s2:" << s2 << "       length: " << s2.Length() << std::endl;

    string s3(s1);
    std::cout << "s3:" << s3 << "       length: " << s3.Length() << std::endl;

    string s4 = s3;
    std::cout << "s4:" << s4 << "       length: " << s4.Length() << std::endl;

    string s5(s1);
    s5 += s2;
    std::cout << "s5:" << s5 << "       length: " << s5.Length() << std::endl;

    string s6(s5);
    std::cout << "s6:" << s6 << "       length: " << s6.Length() << std::endl;

    if (s5 == s6) std::cout << "s5 == s6:       true" << std::endl;

    string s7 = s1 + "456";
    std::cout << "s7:" << s7 << "       length: " << s7.Length() << std::endl;

    string s8 = "456" + s1;
    std::cout << "s8:" << s8 << "       length: " << s8.Length() << std::endl;

    string s9 = s7 + s8;
    std::cout << "s9:" << s9 << "       length: " << s9.Length() << std::endl;

    return 0;
}

原文地址：https://www.cnblogs.com/vlyf/p/11929279.html