C / C++ / MFC

13-Apr-03 3:49

Hi, everyone!

I have often noticed that someone declares a friend
fucntion inside a class (in the .h file of the class)
and give the definition of the function in the .cpp file
of the same class. I want to know whether this
method is correct? Does it have some weak points? Where should
correct place which we give the definition (Note: not the declaration)
of the function?

Another question is, if I define the function like below, what is the
scope of the function? (i.e. where can compiler find the function?)

Here is the sample codes I noticed:

in A.h
--------

class A {

friend int functionA();
void memberfunction();
}
--------

A.cpp
--------
A::memberfunction()
{
//implemention
}

int functionA()
{
//implemention
}

--------

Thanks in advance,
George

MessageBox variation

J.B.12-Apr-03 22:23

J.B.

12-Apr-03 22:23

Hello guys,
I am looking for a function that is similiar to MessageBox function, however, would have ability to include formatted variable in the pop-up windows box.

Best way to illustrate, is something in combination of printf and MessageBox

int number = 3;
printf("Number is : %d", number);

so, might mean doing that in forms of MessageBox
MessageBox("Number is : %d", number);

Is there funtion MFC that could server that purpose?

Thanks in advance for any help.

Brian Shifrin13-Apr-03 0:29

Brian Shifrin

13-Apr-03 0:29

CString myMessage;
myMessage.Format("Number is : %d", number);
MessageBox(myMessage, ..., MB_OK);

Brian

Neville Franks13-Apr-03 0:46

Neville Franks

13-Apr-03 0:46

There isn't an MFC function for this. I use code like the following in ED (see sig) for it's "Do not ask again" message boxs.

MsgBox( TCHAR* pStr, ... )
{
    va_list marker;
    va_start( marker, pStr );
    const int nMaxMsgSize = 10 * 1024;   // we don't know how to calc required size, so pick something large enough.
    TCHAR substmsg[ nMaxMsgSize+1 ] = {0};
    _vsnprintf( substmsg, nMaxMsgSize, pStr, marker );

    MessageBox( hWnd, substmsg, Caption, uType );

    va_end( marker );
}

You need to fill in the missing bits like hWnd etc,

Hope that helps.

Neville Franks, Author of ED for Windows. www.getsoft.com
Make money with our new Affilate program

Jean-Marc Molina13-Apr-03 1:49

Jean-Marc Molina

13-Apr-03 1:49

Hello,

The solution is to first format your string, then display the message box. The best way is probably to use a varlist and to implement your own function. Here is my own:

int AfxMessageBoxFormat (LPCTSTR lpszFormat, ...)<br />
{<br />
	// Build message from parameters<br />
<br />
CString s;<br />
<br />
va_list args;<br />
va_start (args, lpszFormat);<br />
<br />
	s.FormatV (lpszFormat, args);<br />
<br />
	va_end (args);<br />
<br />
	// Message box<br />
<br />
	return AfxMessageBox (s);<br />
}

Hope that helps,
JM

Web: http://goa.ifrance.com

Question about overloading operator time_t.

J. Dunlap13-Apr-03 7:36

J. Dunlap

13-Apr-03 7:36

I don't think there is, but I'm working on just such a thing in C#.

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"An eye for an eye only makes the whole world blind." - Mahatma Gandhi

George212-Apr-03 20:34

12-Apr-03 20:34

Hi, everyone!

Suppose I have a customer class defines a customer
time presentation structure. It has three int member
variables: year, month and day.

I have noticed someone who overloading time_t operator.
But I do not know how to do it, one of which can be reached
at,

--------
http://www.p2ptoolkit.com/classl2t_1_1base_1_1Date.html#a7
--------

Can anyone tell me how to overload time_t operator? Another
question is I do not know how to use a overloaded time_t
operator. Smile | :)

Here is the code I write myself. I do not know whether it is
correct. I still do not know how to use a overloaded time_t
operator of my class. I just write the operator overload function
from my thought that maybe it should be like this. Smile | :)

Can anyone help?

--------
Class MyTime {

int year;
int month;
int day;

MyTime::operator time_t() const
{
struct tm wn = {0};
wn.tm_mday = day;
wn.tm_mon = month;
wn.tm_year = year;
time_t output = mktime(&wn);
return output;
}
}
--------

Thanks in advance,

markkuk13-Apr-03 0:15

markkuk

13-Apr-03 0:15

time_t isn't an operator, so you can't overload it. It's a standard C typedef for representing time. I guess what you really want is a type conversion operator between MyTime and time_t? That overloads the operator (). Your code is correct for overloading the () operator, but don't use MyTime:: prefix when the function definition is inside the class, and the variable output is redundant.

George213-Apr-03 1:28

13-Apr-03 1:28

Thanks, markkuk buddie!

Why do you say variable output is redundant? I think
my type conversion operator is used to convert MyTime
to time_t. So it must return a time_t type.

Can you give me the correct code of the type conversion
operator function in your opinion?

regards,
George

markkuk13-Apr-03 9:57

markkuk

13-Apr-03 9:57

You can simply return mktime(&wn); without assigning the value in a temporary variable. The code would be:

class MyTime {
private:
    int year;
    int month;
    int day;
public:
    operator time_t() const
    {
        struct tm wn = {0};
        wn.tm_mday = day;
        wn.tm_mon = month;
        wn.tm_year = year;
        return mktime(&wn);
    }
};

George213-Apr-03 17:39

13-Apr-03 17:39

Thanks, markkuk buddie!

George

Michael Dunn13-Apr-03 6:11

Michael Dunn

13-Apr-03 6:11

You use the time_t converter just as you do with built-in conversions:

MyTime mt;
time_t time;
 
  mt.year = 1970;
  mt.month = 8;
  mt.day = 11;
  time = mt;    // calls time_t converter

--Mike--
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George213-Apr-03 17:38