C++(2) 函数(strrev, strcpy, sort)

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strrev自定义实现

char *strrev(char *s)
{
    if (s == NULL || s[0] == '\0')
        return s;
    for (char t, *p = s, *q = s + strlen(s) - 1; p < q; p++, q--)
        t = *p, *p = *q, *q = t;
    return s;
}

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strcpy

char * strcpy(char * strDest,const char * strSrc)
{ 
    if ((NULL==strDest)||(NULL==strSrc)) //[1]
        throw "Invalid argument(s)"; //[2]
    char * strDestCopy = strDest; //[3]
    while ((*strDest++=*strSrc++)!='\0'); //[4]
    return strDestCopy;
}                

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sort

//struct
struct struct_char
{
    char* pAlpha;
    int nPriority;
};
bool struct_comp(const struct_char &struct_a, const struct_char &struct_b)
{
    return struct_a.nPriority<struct_b.nPriority;
}
struct_char arrStruct[] = 
　　　　{{"abc",1}, {"yz", 9}, {"ghi", 3}, {"mno", 5}, 
　　　　{"jkl", 4}, {"pqr", 6}, {"def", 2}, {"stu", 7}, 
　　　　{"vwx", 8}};
sort(arrStruct, arrStruct+9, struct_comp);
for(int i=0;i<=8;i++)
    cout<<arrStruct[i].pAlpha << " ";
cout<<endl;

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string(STL)

#include <iostream>
class String
{
public:
    String(const char *str=NULL);//普通构造函数
    String(const String &str);//拷贝构造函数
    String & operator =(const String &str);//赋值函数
    ~String();//析构函数
protected:
private:
    char* m_data;//用于保存字符串
};

//普通构造函数
String::String(const char *str)
{
    if (str==NULL)
    {
        m_data=new char[1]; //对空字符串自动申请存放结束标志'\0'的空间
    　　if (m_data==NULL)//内存是否申请成功
        {
        std::cout<<"申请内存失败！"<<std::endl;
        exit(1);
    　　}
    　　m_data[0]='\0';
    }
    else
    {
        int length=strlen(str);
        m_data=new char[length+1];
        if (m_data==NULL)//内存是否申请成功
        {
            std::cout<<"申请内存失败！"<<std::endl;
            exit(1);
        }
        strcpy(m_data,str);
    }
}
//拷贝构造函数
String::String(const String &str) //输入参数为const型
{
    int length=strlen(str.m_data);
    m_data=new char[length+1];
    if (m_data==NULL)//内存是否申请成功
    {
        std::cout<<"申请内存失败！"<<std::endl;
        exit(1);
    }
    strcpy(m_data,str.m_data);
}
//赋值函数
String& String::operator =(const String &str)//输入参数为const型
{
    if (this==&str) //检查自赋值
        return *this;
    int length=strlen(str.m_data);
    delete [] m_data;//释放原来的内存资源
    m_data= new char[length+1];
    if (m_data==NULL)//内存是否申请成功
    {
        std::cout<<"申请内存失败！"<<std::endl;
        exit(1);
    }
    strcpy(m_data,str.m_data);
    return *this;//返回本对象的引用
}
//析构函数
String::~String()
{
    delete [] m_data;
}

void main()
{
    String a;
    String b("abc");
    system("pause");
}