字符串（string类）

【1】String类基本函数如何实现？

示例代码如下：

#include <iostream>
#include <assert.h>
#include <string>
using namespace std;

class String
{
public:
    String(const char *str = NULL);  // 复合默认构造函数
    String(const String &other);     // 拷贝构造函数
    String & operator=(const String &other);  // 赋值构造函数
    String operator+(const String &s1);       // 双目运算符重载
    ~String();                                // 析构函数
    void PrintData() const;
    
private:
    char *m_data;   //指针成员变量
};

String::String(const char *str)
 {
    cout << "Construction" << endl;
    if (NULL == str)
    {
        m_data = new char[1];
        assert(m_data != NULL);
        *m_data = '\0';
    }
    else
    {
        int length = strlen(str);
        m_data = new char[length + 1];
        assert(m_data != NULL);
        strcpy(m_data, str);
    }
}

 String::String(const String &other)
 {
    cout << "Copy   Construction" << endl;
    int length = strlen(other.m_data);
    m_data = new char[length + 1];
    assert(m_data != NULL);
    strcpy(m_data, other.m_data);
}

String & String::operator=(const String &other)
 {
    cout << "= Construction" << endl;
    if (this == &other)
    {
        return *this;
    }
    delete []m_data;
    int length = strlen(other.m_data);
    m_data = new char[length + 1];
    assert(m_data != NULL);
    strcpy(m_data, other.m_data);
    return  *this;
}

String String::operator+(const String &s1)
{
    cout << "+ operator" << endl;
    String temp;
    delete []temp.m_data;
    temp.m_data = new char[strlen(m_data) + strlen(s1.m_data) + 1];
    strcpy(temp.m_data, m_data);
    strcat(temp.m_data, s1.m_data);
    return temp;
    
}

void String::PrintData() const
{
    cout << m_data << endl;
}

String::~String()
{
    delete []m_data;
}

void  main()
{
    String s1;             // 默认
    s1.PrintData();
    
    String s2("Liuyong");  // 构造函数
    s2.PrintData();
    
    String s3 = "abcde";   // 隐式转换
    s3.PrintData();

    String s4(s3);       // 拷贝构造
    s4.PrintData();

    String s5;
    s5 = s4;               // 赋值构造
    s5.PrintData();

    String s6 = s2 + s3;     //+operator
    s6.PrintData();

    system("pause");
}
 //run out:
 /*
Construction

Construction
Liuyong
Construction
abcde
Copy   Construction
abcde
Construction
= Construction
abcde
+ operator
Construction
Copy   Construction
Liuyongabcde
请按任意键继续. . .
*/

上面是string类的部分函数实现，具体实现了构造函数，拷贝构造函数，赋值构造函数，析构函数，以及实现了深拷贝的示范。

【2】String类详细实现（原旧版本）

#include <cassert>
#include <string>
#include <iostream>
using namespace std;

class String
{
public:
    String();
    String(int n, char c);
    String(const char *source);
    String(const String &s);
    String & operator=(char *s);
    String & operator=(const String &s);
    ~String();
    char &operator[](int i);
    const char &operator[](int i)const;
    String &operator+=(const String &s);
    String &operator+=(const char *s);
    friend ostream & operator<<(ostream &out, String &s);
    friend istream & operator>>(istream &in, String &s);
    friend bool operator<(const String &left, const String &right);
    friend bool operator>(const String &left, const String &right);
    friend bool operator==(const String &left, const String &right);
    friend bool operator!=(const String &left, const String &right);
    int length();
    char *GetData();

private:
    int size;
    char *data;
};

String::String()
{
    data = new char[1];
    assert(data != NULL);
    *data = '\0';
    size = 0;
}

String::String(int n, char c)
{
    data = new char[n + 1];
    assert(data != NULL);
    size = n;
    char *temp = data;
    while (n--)
    {
        *temp++ = c;
    }
    *temp = '\0';
}
String::String(const char *source)
{
    if (NULL == source)
    {
        data = new char[1];
        assert(data != NULL);
        *data = '\0';
        size = 0;
    }
    else
    {
        size = strlen(source);
        data = new char[size + 1];
        assert(data != NULL);
        strcpy(data, source);
    }
}
String::String(const String &s)
{
    data = new char[s.size + 1];
    assert(data != NULL);
    strcpy(data, s.data);
    size = s.size;
}

String & String::operator=(char *s)
{
    if (data != NULL)
    {
        delete []data;
    }
    size = strlen(s);
    data = new char[size + 1];
    assert(data != NULL);
    strcpy(data, s);
    return *this;
}

String &String::operator=(const String &s)
{
    if (this == &s)
    {
        return *this;
    }
    if (data != NULL)
    {
        delete []data;
    }
    size = strlen(s.data);
    data = new char[size + 1];
    assert(data != NULL);
    strcpy(data, s.data);
    return *this;
}

String::~String()
{
    if (data != NULL)
    {
        delete []data;
        data = NULL;
        size = 0;
    }
}

char &String::operator[](int i)
{
    return data[i];
}

const char &String::operator[](int i)const 
{
    return data[i];
}

String &String::operator+=(const String &s)
{
    int len = size + s.size + 1;
    char *pTemp = data;
    data = new char[len];
    assert(data != NULL);
    size = len - 1;
    strcpy(data, pTemp);
    strcat(data, s.data);
    delete []pTemp;
    return *this;
}

String & String::operator+=(const char *s)
{
    if (NULL == s)
    {
        return *this;
    }
    int len = size + strlen(s) + 1;
    char *pTemp = data;
    data = new char[len];
    assert(data != NULL);
    size = len - 1;
    strcpy(data, pTemp);
    strcat(data, s);
    delete []pTemp;
    return  *this;
}

int String::length()
{
    return size;
}

ostream & operator<<(ostream &out, String &s)
{
    for (int i = 0;i < s.length();i++)
    {
        out << s[i] << " ";
    }
    return out;
}

istream & operator>>(istream &in, String &s)
{
    char p[50];
    in.getline(p, 50);
    s = p;
    return in;
}

bool operator<(const String &left, const String &right)
{
    int i = 0;
    while (left[i] == right[i] && left[i] != 0 && right[i] != 0)
    {
        i++;
    }
    return left[i] - right[i] <0 ? true : false;
}

bool operator>(const String &left, const String &right)
{
    int i = 0;
    while (left[i] == right[i] && left[i] != 0 && right[i] != 0)
    {
        i++;
    }
    return left[i] - right[i] > 0 ? true : false;
}

bool operator ==(const String &left, const String &right)
{
    int i = 0;
    while (left[i] == right[i] && left[i] != 0 && right[i] != 0)
    {
        i++;
    }
    return (left[i] == right[i]) ? true : false ;
}

bool operator !=(const String &left, const String &right)
{
    int i = 0;
    while (left[i] == right[i] && left[i] != 0 && right[i] != 0)
    {
        i++;
    }
    return (left[i] == right[i]) ?  false : true;
}

void main()
{
    String str(3,'a');
    String str1(str);
    String str2("asdf");
    String str3;

    cout << "str: " << str << endl;
    cout << "str1: " << str1 << endl;
    cout << "str2: " << str2 << endl;
    cout << "str3: " << str3 << endl;

    str3 = str2;
    cout << "str2: " << str2 << endl;
    cout << "str3: " << str3 << endl;

    str3 = "12awee";
    cout << "str3: " << str3 << endl;

    cout << "str3[2]= " << str3[2] << endl;

    str3 += "1234";
    cout << "str3: " << str3 << endl;

    str3 += str1;
    cout << "str3: " << str3 << endl;

    String t1 = "1234";
    String t2 = "1234";
    String t3 = "12345";
    String t4 = "12335";

    cout << "t1 == t2 ? " << (t1 == t2) << endl;
    cout << "t1 < t3 ? " << (t1 < t3) << endl;
    cout << "t1 > t4 ? " << (t1 > t4) << endl;
    cout << "t1 != t4 ? " << (t1 != t4) << endl;

    system("pause");
}
// run out:
/*
str: a a a
str1: a a a
str2: a s d f
str3:
str2: a s d f
str3: a s d f
str3: 1 2 a w e e
str3[2]= a
str3: 1 2 a w e e 1 2 3 4
str3: 1 2 a w e e 1 2 3 4 a a a
t1 == t2 ? 1
t1 < t3 ? 1
t1 > t4 ? 1
t1 != t4 ? 1
请按任意键继续. . .
*/

【3】String类详细实现（最新版本）（C++11后）

VS2017环境下：

#include <cassert>
#include <string>
#include <iostream>
using namespace std;

class String
{
public:
    String();
    String(int n, char c);
    String(const char *source);
    String(const String &s);
    String(String && s);
    String & operator=(char *s);
    String & operator=(const String &s);
    String & operator=(String &&s);
    ~String();

    char &operator[](int i);
    const char &operator[](int i) const;
    String &operator+=(const String &s);
    String &operator+=(const char *s);
    
    friend ostream & operator<<(ostream &out, String &s);
    friend istream & operator>>(istream &in, String &s);
    friend bool operator<(const String &left, const String &right);
    friend bool operator>(const String &left, const String &right);
    friend bool operator==(const String &left, const String &right);
    friend bool operator!=(const String &left, const String &right);

    int getSize() const;
    void setSize(int nSize);
    char* getData() const;
    void setData(char *pData);

private:
    void init();

private:
    int m_size;
    char *m_data;
};

void String::init()
{
    m_data = new char[1];
    assert(m_data != NULL);
    *m_data = '\0';
    m_size = 0;
}

String::String()
{
    init();
}

String::String(int n, char c)
{
    m_data = new char[n + 1];
    assert(m_data != NULL);
    m_size = n;
    char *temp = m_data;
    while (n--)
    {
        *temp++ = c;
    }
    *temp = '\0';
}

String::String(const char *source)
{
    if (NULL == source)
    {
        init();
    }
    else
    {
        m_size = strlen(source);
        m_data = new char[m_size + 1];
        assert(m_data != NULL);
        strcpy_s(m_data, (m_size + 1), source);
    }
}
String::String(const String &s)
{
    m_data = new char[s.m_size + 1];
    assert(m_data != NULL);
    strcpy_s(m_data, (s.m_size + 1), s.m_data);
    m_size = s.m_size;
}

String::String(String &&s)
{
    cout << "call move ctor" << endl;
    m_data = s.getData();
    m_size = s.getSize();
    s.setData(NULL);
    s.setSize(0);
}

String & String::operator=(char *s)
{
    if (m_data != NULL)
    {
        delete []m_data;
    }
    m_size = strlen(s);
    m_data = new char[m_size + 1];
    assert(m_data != NULL);
    strcpy_s(m_data, (m_size + 1), s);
    return (*this);
}

String &String::operator=(const String &s)
{
    if (this == &s)
    {
        return *this;
    }
    if (m_data != NULL)
    {
        delete []m_data;
    }
    m_size = strlen(s.m_data);
    m_data = new char[m_size + 1];
    assert(m_data != NULL);
    strcpy_s(m_data, (m_size + 1), s.m_data);
    return (*this);
}

String & String::operator=(String &&s)
{
    cout << "call move operator=" << endl;
    if (this == &s)
    {
        return (*this);
    }
    if (m_data != NULL)
    {
        delete []m_data;
    }
    m_data = s.getData();
    m_size = s.getSize();
    s.setData(NULL);
    s.setSize(0);
    return (*this);
}

String::~String()
{
    if (m_data != NULL)
    {
        delete []m_data;
        m_data = NULL;
        m_size = 0;
    }
}

char &String::operator[](int i)
{
    return m_data[i];
}

const char &String::operator[](int i) const
{
    return m_data[i];
}

String &String::operator+=(const String &s)
{
    int len = m_size + s.m_size + 1;
    char *pTemp = m_data;
    m_data = new char[len];
    assert(m_data != NULL);
    strcpy_s(m_data, (m_size + 1), pTemp);
    strcat_s(m_data, len, s.m_data);
    m_size = len - 1;
    delete []pTemp;
    return (*this);
}

String & String::operator+=(const char *s)
{
    if (NULL == s)
    {
        return (*this);
    }
    int len = m_size + strlen(s) + 1;
    char *pTemp = m_data;
    m_data = new char[len];
    assert(m_data != NULL);
    strcpy_s(m_data, (m_size + 1), pTemp);
    strcat_s(m_data, len, s);
    m_size = len - 1;
    delete []pTemp;
    return (*this);
}

int String::getSize() const
{
    return m_size;
}

void String::setSize(int nSize)
{
    this->m_size = nSize;
}

char* String::getData() const
{
    return m_data;
}

void String::setData(char *pData)
{
    if (NULL == pData)
    {
        init();
    }
    else
    {
        m_data = pData;
    }
}

ostream & operator<<(ostream &out, String &s)
{
    for (int i = 0; i < s.getSize(); ++i)
    {
        out << s[i] << " ";
    }
    return out;
}

istream & operator>>(istream &in, String &s)
{
    char p[50];
    in.getline(p, 50);
    s = p;
    return in;
}

bool operator<(const String &left, const String &right)
{
    int i = 0;
    while (left[i] == right[i] && left[i] != 0 && right[i] != 0)
    {
        i++;
    }
    return (left[i] - right[i] < 0);
}

bool operator>(const String &left, const String &right)
{
    int i = 0;
    while (left[i] == right[i] && left[i] != 0 && right[i] != 0)
    {
        i++;
    }
    return (left[i] - right[i] > 0);
}

bool operator==(const String &left, const String &right)
{
    int i = 0;
    while (left[i] == right[i] && left[i] != 0 && right[i] != 0)
    {
        i++;
    }
    return (left[i] == right[i]);
}

bool operator!=(const String &left, const String &right)
{
    int i = 0;
    while (left[i] == right[i] && left[i] != 0 && right[i] != 0)
    {
        i++;
    }
    return (left[i] != right[i]);
}

int main()
{
    String str(3, 'a');
    String str1(str);
    String str2("asdf");
    String str3;
    cout << "str: " << str << endl;
    cout << "str1: " << str1 << endl;
    cout << "str2: " << str2 << endl;
    cout << "str3: " << str3 << endl;

    // 赋值
    str3 = str2;
    cout << "str2: " << str2 << endl;
    cout << "str3: " << str3 << endl;

    // 移动赋值
    str3 = "12awee";  // call move operator=
    cout << "str3: " << str3 << endl;
    cout << "str3[2]= " << str3[2] << endl;

    str3 += "1234";
    cout << "str3: " << str3 << endl;

    str3 += str1;
    cout << "str3: " << str3 << endl;
    
    // 移动构造函数
    String str4(move(str2));  // call move ctor
    cout << "str4: " << str4 << endl;

    // 移动赋值
    String str5;
    str5 = move(str3); // call move operator=
    cout << "str5: " << str5 << endl;

    // 比较
    String t1 = "1234";
    String t2 = "1234";
    String t3 = "12345";
    String t4 = "12335";
    cout << "t1 == t2 ? " << (t1 == t2) << endl;
    cout << "t1 < t3 ? " << (t1 < t3) << endl;
    cout << "t1 > t4 ? " << (t1 > t4) << endl;
    cout << "t1 != t4 ? " << (t1 != t4) << endl;

    // 输入
    String strInput;
    cout << "Please input string " << endl;
    cin >> strInput;
    cout << "strInput: " << strInput << endl;

    system("pause");
}

// run out:
/*
str: a a a
str1: a a a
str2: a s d f
str3:
str2: a s d f
str3: a s d f
call move operator=
str3: 1 2 a w e e
str3[2]= a
str3: 1 2 a w e e 1 2 3 4
str3: 1 2 a w e e 1 2 3 4 a a a
call move ctor
str4: a s d f
call move operator=
str5: 1 2 a w e e 1 2 3 4 a a a
t1 == t2 ? 1
t1 < t3 ? 1
t1 > t4 ? 1
t1 != t4 ? 1
Please input string
kaizen
strInput: k a i z e n
请按任意键继续. . .
*/

Good Good Study，Day Day Up.

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