why does the static member function work like that?

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hello,erveryone,recently I meeted a question:

#include <iostream.h>
#include <string.h>

class MyTime
{
public:
      char m_MyName[100];
     static int m_count
      MyTime(char *p1,char *p2,int i,int j,int k);
      ~MyTime();
      void ShowTime();
     static void GetCount();
     static void GetTime(MyTime); 
protected:
       char m_MyGender[5];
private
       int m_Hour;
      int m_Minute;
      int m_Second;
};
int MyTime::m_count=0;
MyTime::MyTime(char *p1,char *p2,int i,int j,int k)
{
    strcpy(m_MyName,p1);
    strcpy(m_MyGender,p2);
    m_Hour=i;
    m_Minute=j;
    m_Second=k; 
}
void MyTime::ShowTime()
{
     cout<<m_MyName<<" tell:it is:"<<m_Hour<<":"<<m_Minute<<":"<<m_Second<<endl;
}
MyTime::~MyTime()
{
     m_Hour=m_Hour+1;
     m_Minute=m_Minute+1;
     m_Second=m_Second+1;
     ShowTime();
}
void MyTime::GetCount()
{
    cout<<"m_count="<<m_count<<endl;
}
void MyTime::GetTime(MyTime t)
{
     cout<<"time: "<<t.m_Hour<<":"<<t.m_Minute<<":"<<t.m_Second<<endl;
}

 
void main()
{
   char *p1="sunshine";
   char *p2="man";  
   MyTime mytime(p1,p2,10,10,10);
   MyTime::m_count++;
   mytime.GetCount();
   MyTime::GetTime(mytime);
 }
The result is:
m_count=1
time: 10:10:10
sunshine  tell:it is:11:11:11
sunshine  tell:it is:11:11:11
Press any key to continue</string.h></iostream.h>

Just now,I was confused that why "sunshine tell:it is:11:11:11" appeared twice.After checking the code,I found it was the reason of ~MyTime(),which worked twice.And when I deleted the "MyTime::GetTime(mytime)",it worked correctly.
Now I don't know why it works like that,And you? I'm looking forward to your answer! ^_^^_^^_^

Posted 2-Aug-11 0:06am

Rslboy

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2 solutions

Solution 1

This is because the object is destroyed. Check out what happens in the destructor ~MyTime() ;-) It looks like the destructor is already called and destruction and copying gets somewhat tangled up. You could output some extra information to the screen (like from the destructor) to see what is happening when.

Good luck!

Posted 2-Aug-11 0:53am

E.F. Nijboer

Updated 2-Aug-11 1:02am

v2

Comments

Rslboy 2-Aug-11 9:00am

Thanks for your answer!it is the reason of the way the static member function(GetTime)is defined.As Cpallini said,I got the resolution!:-):-)

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CPallini · Accepted Answer · 2011-08-02T01:31:00

Solution 2

It happens because GetTime method gets its parameter by value, hence a temporary object is created (and then destroyed when such method terminates).
Change GetTime signature (updated as per Philippe Mori suggestion)

(prototype in class)

C++

static void GetTime(const MyTime & t);

(implementation)

C++

void MyTime::GetTime(const MyTime & t)
{
  //...
}

if you don't like such a behaviour.

Posted 2-Aug-11 1:31am

CPallini

Updated 2-Aug-11 21:09pm

v8

Comments

Rslboy 2-Aug-11 8:56am

Thanks very much!the resolution you said is right for that,谢谢！:-):-)

CPallini 2-Aug-11 9:00am

So you gave me 1?
:-)

_Zorro_ 2-Aug-11 9:04am

+5, there you go :)

CPallini 2-Aug-11 9:05am

Thank you, masked hero!

Philippe Mori 2-Aug-11 22:12pm

Should be static void GetTime(const MyTime & t) since you don't want to modify the time.

CPallini 3-Aug-11 3:07am

Sure, thank you.