第三十九课 字符串类的创建（上）

 

c++中用STL封装了字符串类，但是这是不通用的。

 

 

 

 实现字符串类，就是用面向对象的方式封装C语言对字符串的操作。

添加DTString.h文件：

#ifndef DTSTRING_H
#define DTSTRING_H

#include "Object.h"

namespace DTLib
{

class String : Object
{
protected:
    char* m_str;
    int m_length;

    void init(const char* s);
public:
    String();
    String(char c);
    String(const char* s);
    String(const String& s);

    int length() const;
    const char* str() const;

    bool operator == (const String& s) const;
    bool operator == (const char* s) const;

    bool operator != (const String& s) const;
    bool operator != (const char* s) const;

    bool operator > (const String& s) const;
    bool operator > (const char* s) const;

    bool operator < (const String& s) const;
    bool operator < (const char* s) const;

    bool operator >= (const String& s) const;
    bool operator >= (const char* s) const;

    bool operator <= (const String& s) const;
    bool operator <= (const char* s) const;

    String operator + (const String& s) const;
    String operator + (const char* s) const;
    String operator += (const String& s);
    String operator += (const char* s);

    String& operator = (const String& s);
    String& operator = (const char* s);
    String& operator = (char c);

    ~String();
};

}


#endif // DTSTRING_H

 

添加DTString.cpp文件：

#include <cstring>
#include <cstdlib>
#include "DTString.h"
#include "Exception.h"

using namespace std;

namespace DTLib
{

void String::init(const char* s)
{
    m_str = strdup(s);

    if( m_str )
    {
        m_length = strlen(m_str);
    }
    else
    {
        THROW_EXCEPTION(NoEnoughMemoryException, "No memory to create string object ...");
    }
}

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

String::String(const char* s)
{
    init(s ? s : "");   //空指针就转换成空字符串
}

String::String(const String& s)
{
    init(s.m_str);
}

String::String(char c)
{
    char s[] = {c, '\0'};

    init(s);
}

int String::length() const
{
    return m_length;
}

const char* String::str() const
{
    return m_str;
}

bool String::operator == (const String& s) const
{
    return ( strcmp(m_str, s.m_str) == 0 );
}

bool String::operator == (const char* s) const
{
    return ( strcmp(m_str, s ? s : "") == 0 );
}

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

bool String::operator != (const char* s) const
{
    return !(*this == s);
}

bool String::operator > (const String& s) const
{
    return (strcmp(m_str, s.m_str) > 0);
}

bool String::operator > (const char* s) const
{
    return (strcmp(m_str, s ? s : "") > 0);
}

bool String::operator < (const String& s) const
{
    return (strcmp(m_str, s.m_str) < 0);
}

bool String::operator < (const char* s) const
{
    return (strcmp(m_str, s ? s : "") < 0);
}

bool String::operator >= (const String& s) const
{
    return (strcmp(m_str, s.m_str) >= 0);
}

bool String::operator >= (const char* s) const
{
    return (strcmp(m_str, s ? s : "") >= 0);
}

bool String::operator <= (const String& s) const
{
    return (strcmp(m_str, s.m_str) <= 0);
}

bool String::operator <= (const char* s) const
{
    return (strcmp(m_str, s ? s : "") <= 0);
}

String String::operator + (const String& s) const
{
    return (*this + s.m_str);
}

String String::operator + (const char* s) const
{
    String ret;

    int len = m_length + strlen(s ? s : "");

    char* str = reinterpret_cast<char*>(malloc(len + 1));

    if( str )
    {
        strcpy(str, m_str);
        strcat(str, s ? s : "");

        free(ret.m_str);

        ret.m_str = str;
        ret.m_length = len;
    }
    else
    {
        THROW_EXCEPTION(NoEnoughMemoryException, "No memory to create str object...");
    }

    return ret;
}
String String::operator += (const String& s)
{
    return (*this = *this + s.m_str);
}

String String::operator += (const char* s)
{
    return (*this = *this + s);
}

String& String::operator = (const String& s)
{
    return (*this = s.m_str);
}

String& String::operator = (const char* s)
{
    if( m_str != s )
    {
        char* str = strdup(s ? s: "");

        if( str )
        {
            free(m_str);

            m_str = str;
            m_length = strlen(m_str);
        }
        else
        {
            THROW_EXCEPTION(NoEnoughMemoryException, "No memory to create str object...");
        }
    }

    return *this;
}

String& String::operator = (char c)
{
    char s[] = {c, '\0'};

    return (*this = s);
}

String::~String()
{
    free(m_str);
}

}

 

测试程序如下：

#include <iostream>
#include "DTString.h"

using namespace std;
using namespace DTLib;

void test_1()
{
    cout << "test_1() begin ... " << endl;

    String s;

    s = 'D';

    cout << s.str() << endl;
    cout << s.length() << endl;
    cout << (s == "D") << endl;
    cout << (s > "CCC") << endl;

    s += " Zhang ";

    cout << s.str() << endl;
    cout << s.length() << endl;
    cout << (s == "D Zhang ") << endl;

    cout << "test_1() end ... " << endl;
}

void test_2()
{
    cout << "test_2() begin ... " << endl;

    String a[] = {"E", "D", "C", "B", "A"};
    String min = a[0];

    for(int i = 0; i < 5; i++)
    {
        if( min > a[i] )
        {
            min = a[i];
        }
    }

    cout << "min = " << min.str() << endl;

    cout << "test_2() end ... " << endl;
}

int main()
{
    test_1();

    test_2();

    return 0;
}

运行结果如下：

 

小结：