Re: C++ syntax: how to init non-default constructor for array? - C / C++ / MFC Discussion Boards

Re: Error in loading accelerator table

Stephen Hewitt20-Jun-10 19:11

Stephen Hewitt

20-Jun-10 19:11

Check the HINSTANCE handle is referring to the correct DLL.

Steve

Re: Error in loading accelerator table

Pryabu20-Jun-10 19:32

Pryabu

20-Jun-10 19:32

thank u. its working.

Visual Studio 2010 Release Candidate to Trial?

Paul Hooper20-Jun-10 16:56

Paul Hooper

20-Jun-10 16:56

I am currently using the Visual Studio 2010 Release Candidate and have ordered a full version ... but ... my order seems to be stuck "On Order". The expected dispatch date is today but I am not holding my breath. I have eight days left on the RC and I am beginning to get a little nervous.

Does anyone know if I can upgrade from the RC to the trial version to cover the gap? Any experiences or pointers worth sharing?

Paul Hooper

If you spend your whole life looking over your shoulder, they will get you from the front instead.

C++ syntax: how to init non-default constructor for array?

includeh1020-Jun-10 13:33

includeh10

20-Jun-10 13:33

Code:

class MyClass
{
public:
     MyClass(int iType);
};

class YourClass
{
public:
     YourClass();
     MyClass mys[2];
};

How to init constructor of MyClass for array mys[2] at:

YourClass::YourClass()
{

}

Impossible?

modified on Sunday, June 20, 2010 7:44 PM

Re: C++ syntax: how to init non-default constructor for array?

«_Superman_»20-Jun-10 15:30

«_Superman_»

20-Jun-10 15:30

You can create an Init method and call it for each element in the array.

«_Superman_»

I love work. It gives me something to do between weekends.

Microsoft MVP (Visual C++)

Polymorphism in C

Re: C++ syntax: how to init non-default constructor for array?

Stephen Hewitt20-Jun-10 17:11

Stephen Hewitt

20-Jun-10 17:11

Good question. I can't believe I've never ran into this before. I don't see any clean way around it.

Steve

Re: C++ syntax: how to init non-default constructor for array?

«_Superman_»20-Jun-10 18:36

«_Superman_»

20-Jun-10 18:36

I've come across this a couple of times before and I didn't find any other method than to assign values separately to each object in the array.

«_Superman_»

I love work. It gives me something to do between weekends.

Microsoft MVP (Visual C++)

Polymorphism in C

Re: C++ syntax: how to init non-default constructor for array?

Emilio Garavaglia20-Jun-10 21:00

Emilio Garavaglia

20-Jun-10 21:00

Unfortunately, the language don't specify any construct to pass parameters to the array constructing elements.

std::vector does this, essentially with a trick (to allow array grow and shrink it doesn't allocate "array" but "bulk buffers".

You can emulate this trick yourself this way:

///Elements requiring explicit initialization
/// \note Elements don't have a default Ctor.
class Element
{
public:
    /// init an element
    Element(ParamType _a)
    { ... }
private:
    //your implementation
};

static const size_t BUFSZ = ...;

/// a class aggragating \c BUFSZ elements
class Aggregate
{
public:
    /// initialize with _a
    Aggregate(ParamType _a) :vector()
    { 
        vector = reinterpret_cast<Element*>(buffer);
        for(size_t i=0; i<BUFSZ; ++i)
            new(vector+i)Element(_a); //< USE PLACEMENT NEW
    }
    /// do proper element copy (not just bulk memory copy)
    Aggregate(const Aggregate& _s)
    {
        vector = reinterpret_cast<Element*>(buffer);
        for(size_t i=0; i<BUFSZ; ++i)
            new(vector+i)Element(_s.vector[i]); //< USE PLACEMENT NEW to construct copies
    }
    /// do proper element destruction
    ~Aggregate()
    {
        for(size_t i=0; i<BUFSZ; ++i)
            vector[i].~Element(); //< DO EXPLICIT DESTRUCTION
    }
private:
    char buffer[BUFSZ*sizeof(Element)];
    Element* vector;    
};

The advantage respect to std::vector is that memory is not allocated dynamically, but - Being BUFZ statically note, it can stay into the aggregate space.

The "other way" is to let Elements to default-construct someway, and than assign them the required values.

It mostly depend on the fact you can -or not- accept a default initialization for Element-s putting them in a sort of invalid state until they are assigned.

2 bugs found.
> recompile ...
65534 bugs found.
D'Oh! | :doh:

Re: C++ syntax: how to init non-default constructor for array?

Aescleal20-Jun-10 22:58

Aescleal

20-Jun-10 22:58

If you don't have to use an array (and generally there's no point), can use a vector and want each element initialised to the same value:

class YourClass
{
    public:
        YourClass() : mys( 2, MyClass( 7 ) )
        {}

        std::vector<MyClass> mys;
};

will do the trick. If you want different values then it's a bit trickier unless they're known at compile time. I won't bother going over that here though, please post if you want to know how to do it.

If you want them to all have different values and have an array set at compile time you're going to have to manage the construction and destruction yourself into a raw memory buffer:

class B
{
	public:
		B( int ) {}
};

class A
{
	public:
		A() : values_( reinterpret_cast<B (&)[2]>( raw_buff_[ 0 ] ) )
		{
		}

	private:
		char raw_buff_[ sizeof( B[2] ) ];
		B (&values_)[2];
};

How you write the body of the constructor for A then depends on whether you want one value or different values. If you want the same value you can use initialized_fill:

A() : values_( reinterpret_cast<B (&)[2]>( raw_buff_[ 0 ] ) )
{
	std::uninitialized_fill( &values_[ 0 ], &values_[ 2 ], B( 7 ) );
}

If you want to have different values you'll have to use something like construct (if your standard library supports it, it was in the SGI STL but not in the standard) or write your own:

template <class T1, class T2> void construct(T1* p, const T2& value)
{
	new( p ) T1( value );
}

and then use it to implement your constructor:

A() : values_( reinterpret_cast<B (&)[2]>( raw_buff_[ 0 ] ) )
{
	construct( &values_[ 0 ], B( 1 ) );
	construct( &values_[ 1 ], B( 2 ) );
}

In either case you're going to want a destructor as you have to manually run the destructor for the elements in the array:

template <class T> void destroy(T* p)
{
    p->~T();
}

~A()
{
    destory( &values_[ 0 ] );
    destroy( &values_[ 1 ] );
}

Generally don't use C-style arrays unless you really have to. There's usually a solution in the standard library that's (almost) as good and far less fiddly to use.

Cheers,

Ash

Edited: Forgot the destructor.

CString::GetAt() problem

ForNow20-Jun-10 8:33

ForNow

20-Jun-10 8:33

Hi,

I am tracing code with the Visual Studio Debugger and when I hit upon CString::GetAt(8) statment

seems like I lose control meaning the statment Following the GetAt is a "if"

statement but when the debugger encounters the GetAt it takes off probably to the codde where the GetAt

ia and never returns

Re: CString::GetAt() problem

«_Superman_»20-Jun-10 15:35

«_Superman_»

20-Jun-10 15:35

You question is not very clear to me.
I'm assuming you're having trouble when stepping into the MFC code.

You can use the following shortcut keys while debugging -
F10 will step over the function.
F11 will step into the function.
Shift + F11 will step out of the function.

Here is a link to the complete list of debugging shortcut keys -
Debugger Shortcut Keys[^]

«_Superman_»

I love work. It gives me something to do between weekends.

Microsoft MVP (Visual C++)

Polymorphism in C

Re: CString::GetAt() problem

ForNow21-Jun-10 1:59

ForNow

21-Jun-10 1:59

when I step thru it

it just goes off somewhere

meaning the yellow arrow disappears and my main window is displayed

seems like it bypassed executing some code

receiving data from serial port into two dialogs in an application

l_d20-Jun-10 6:48

l_d

20-Jun-10 6:48

i am receving data from serial port and i have to display in two dialog boxes,but the data is not being received in second dialog.The first dialog is parent of second dialog.I am using MSComm ActiveX controls. i am closing the port and opening again.

Please help me to solve the problem.
Thanks in advance

Re: receiving data from serial port into two dialogs in an application

«_Superman_»20-Jun-10 15:38

«_Superman_»

20-Jun-10 15:38

There is probably no data available to read.
The serial port by default acts like a pipe.
Data is removed from the port after it is read.
So the parent dialog is probably reading all the data leaving nothing available for the child dialog.
Also, please do all error checking and see if any of the calls are failing.

«_Superman_»

I love work. It gives me something to do between weekends.

Microsoft MVP (Visual C++)

Polymorphism in C

Re: receiving data from serial port into two dialogs in an application

Cedric Moonen20-Jun-10 20:35

Cedric Moonen

20-Jun-10 20:35

If I were you, I would write a wrapper around your serial port (and most probably get rid of MSComm active X). This class would then store the data so that mutliple parts of your application can retrieve the required information.

Cédric Moonen
Software developer

Charting control [v3.0]
OpenGL game tutorial in C++

Can someone give a detail of this sample coder why the result is 9,and not 4??

wbgxx20-Jun-10 4:35

wbgxx

20-Jun-10 4:35

#include <iostream.h>
int main()
{
    int x=1,y;
    y= ++x*++x;
    cout << x << endl;
    cout << y <<endl;
    return 0;
}

Re: Can someone give a detail of this sample coder why the result is 9,and not 4??

CPallini20-Jun-10 4:51

CPallini

20-Jun-10 4:51

Because you shouldn't use the pre-increment operator that way.
Smile | :)

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.

This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong.
-- Iain Clarke

[My articles]

Re: Can someone give a detail of this sample coder why the result is 9,and not 4??

hasani200720-Jun-10 4:51

hasani2007

20-Jun-10 4:51

Hello
It's not very hard. answer of this simple question is :
YOU WRITE ++x TWICE.y=++x[first time]*++x[second time]

don't forget to vote me.
BYE...

Re: Can someone give a detail of this sample coder why the result is 9,and not 4??

Richard MacCutchan20-Jun-10 5:49

Richard MacCutchan

20-Jun-10 5:49

++x                  // x now = 2
    *                // will multiply in a moment
      ++x            // x now = 3
// now multiply x(3) by x(3) = 9

You should not use expressions like this as they may not give the results you expect.

It's time for a new signature.

Re: Can someone give a detail of this sample coder why the result is 9,and not 4??

Rajesh R Subramanian20-Jun-10 6:42

Rajesh R Subramanian

20-Jun-10 6:42

Richard MacCutchan wrote:
You should not use expressions like this as they may not give the results you expect.

I welcome you to take a look at our codebase. Laugh | :laugh:

Workout progress:

Current arm size: 14.4in

Desired arm size: 18in

Next Target: 15.4in by Dec 2010

Current training method: HIT

Re: Can someone give a detail of this sample coder why the result is 9,and not 4??

Hristo-Bojilov20-Jun-10 6:23

Hristo-Bojilov

20-Jun-10 6:23

Note that priority of ++ operation is higher than *.If you have y= ++x*x++ it should be 4.
I would recommend you not to use such features because it makes code very hard to understand and modify.
Keep it simple and you will avoid getting in troubles. Smile | :)

Life is a stage and we are all actors!

Re: Can someone give a detail of this sample coder why the result is 9,and not 4??

Luc Pattyn20-Jun-10 11:04

Luc Pattyn

20-Jun-10 11:04

Hristo Bojilov wrote:
Keep it simple

I agree.

BTW: the exact order of the expression evaluation and the side-effects has been undefined in many languages for a long time. However IMO a compiler should issue a warning whenever you rely on assumptions, i.e. undefined results.

Smile | :)

Luc Pattyn [Forum Guidelines] [Why QA sucks] [My Articles] Nil Volentibus Arduum

Please use < PRE > tags for code snippets, it preserves indentation, and improves readability.

Re: Can someone give a detail of this sample coder why the result is 9,and not 4?? - sorta repost

Iain Clarke, Warrior Programmer21-Jun-10 0:26

Iain Clarke, Warrior Programmer

21-Jun-10 0:26

This is basically the same question as:
http://www.codeproject.com/Messages/3507402/A-Doubt.aspx[^]

Where in your class does your colleague sit? I expect you both to get high marks now!

Iain.

I am one of "those foreigners coming over here and stealing our jobs". Yay me!

How to find the correct coordinate?

hasani200720-Jun-10 4:28

hasani2007

20-Jun-10 4:28

Hello all
this is my maze. when the worm reach to wall it passes the wall and sometime it stops.

#include <stdio.h>
#include <conio.h>

int dir=0;
char wall[40][50]={
   {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1},
   {1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,1,1,1,1},
   {1,1,0,0,0,0,0,0,0,1,1,1,0,0,0,0,0,1,1,1,1,1,1,1,0,1},
   {1,1,0,1,0,0,0,0,0,1,1,1,0,0,0,0,0,1,1,1,1,1,1,1,0,1},
   {1,0,0,0,0,0,1,1,1,1,1,0,0,0,0,0,0,1,0,0,0,0,0,0,1,1},
   {1,1,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,1,1,1,1,0,1,1,0,1},
   {1,0,0,0,0,0,1,1,1,1,1,0,0,0,0,0,0,1,0,0,0,0,0,0,1,1},
   {1,1,1,1,1,0,0,0,1,1,1,0,0,0,0,1,1,1,1,0,0,0,1,1,0,1},
   {1,0,1,0,0,1,1,1,1,1,1,1,1,1,0,0,0,0,0,0,0,0,0,0,1,1},
   {1,1,1,1,1,1,1,1,0,1,0,0,0,1,1,0,0,0,0,0,0,0,0,0,1,1},
   {1,1,0,1,0,0,0,0,0,0,1,1,1,0,0,0,0,0,1,1,1,1,1,1,0,1},
   {1,0,0,0,0,0,1,1,1,1,1,0,0,0,0,0,0,1,0,0,0,0,0,0,1,1},
   {1,1,1,1,1,0,0,0,1,1,1,0,0,0,0,1,1,1,1,0,0,0,1,1,0,1},
   {1,0,1,0,0,1,1,1,1,1,1,1,1,1,0,0,0,0,0,0,0,0,0,0,0,1},
   {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1},
};

/* prototypes */
create_wall();
arrow_keys();
/* end of prototypes */

void main()
{
   int a=3,b=2;
   create_wall();
   lbl : arrow_keys();
   if (dir==72){
   b-=1;
      if (wall[a][b]==0){wall[a][b]='*';gotoxy(a,b); printf("%c",wall[a][b]);goto lbl;}
      else b+=1;goto lbl;
   }
   if (dir==75){
   a-=1;
      if (wall[a][b]==0){wall[a][b]='*';gotoxy(a,b); printf("%c",wall[a][b]);goto lbl;}
      else a+=1;goto lbl;
   }
   if (dir==77){
   a+=1;
      if (wall[a][b]==0){wall[a][b]='*';gotoxy(a,b); printf("%c",wall[a][b]);goto lbl;}
      else a-=1;goto lbl;
   }
   if (dir==80){
   b+=1;
      if (wall[a][b]==0){wall[a][b]='*';gotoxy(a,b); printf("%c",wall[a][b]);goto lbl;}
      else b-=1;goto lbl;
   }
   if (dir==0) {printf("exit");}
}




/* function to create the walls */
create_wall(){
   clrscr();
   int i,j;
   for(i=0;i<15;i++){
      for(j=0;j<26;j++){
      if (wall[i][j]==1) printf("²");
      else printf(" ");
      }
   printf("\n");
   }
   gotoxy(2,2);
   printf("**");
}
/* end of create_wall function */
////////////////////////////////////
/* function to define arrow keys */
int arrow_keys()
   {
   int ch;
   while(1)
      {
      ch=getch();
      if(ch==0)
	 {
	 ch=getch();
	 if(ch==72) {dir=72; break;}
	 if(ch==75) {dir=75; break;}
	 if(ch==77) {dir=77; break;}
	 if(ch==80) {dir=80; break;}
	 }
      else dir=0;
      break;

      }
}

Where is the problem.

Re: How to find the correct coordinate?

Niklas L21-Jun-10 0:44

Niklas L

21-Jun-10 0:44

Here are a few ideas for you to make life easier in the future:

1. Don't use global variables when you don't have to. In your case, wall might be acceptable, but dir should not be global.
2. Don't confuse others by writing wall[40][50] and only initialize 15/26.
3. If wall is global, add globals for the wall bounds as well. You don't want to use hard coded values (like 15 and 26) anywhere else but very close to you wall definition. (you can't trust sizeof() operator either the way you have done it)
4. Be consistent in your naming. Don't use indexes a and b in one place, and i and j in another for the same thing. x and y would do just fine.
5. Do not use labels and goto where a simple loop will be enough. Your code will be hard to follow and maintain, even if it's correct. If you need a label, and it will be a long time before you do, give it a meaningful name.
6. Let arrow_keys return its value instead of changing a global variable. It's defined to return an int, but never does. So is also create_wall() by the way.
7. Use constant identifiers instead of hard coded numbers. An enum type is well suited for your direction variable. Again, think of naming.
8. printf("%c", ...)? Have a look at putc().
9. Indentation looks a bit random, and so does placement of curly brackets. Adopt a consistent style.

That said, finding these kinds of bugs is an easy job if you step through the code in a debugger, inspecting indexes into your wall matrix.

But clean up your code first.

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