C / C++ / MFC Discussion Boards

Divyang Mithaiwala6-May-09 23:27

6-May-09 23:27

A code you have past here is the exact code that is in your system?

But if you have taken temp as array (char temp[XX]) then you might get error which you told. But a code that we are sawing has no that kind of error.

Do not trust a computer...
Always check what computer is doing

regards,
Divyang Mithaiwala
Software Engineer

modified on Thursday, May 7, 2009 5:38 AM

Re: string concatenation using pointer

CPallini6-May-09 23:33

CPallini

6-May-09 23:33

Sure?

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: string concatenation using pointer

_AnsHUMAN_ 6-May-09 23:39

_AnsHUMAN_

6-May-09 23:39

Divyang Mithaiwala wrote:
Because if you have taken temp as array (char temp[XX]) then you might get error

Why so?

Divyang Mithaiwala wrote:
But a code that we are sawing has no that kind of error.

Did you trust your computer to check if there was a runtime error? Smile | :)

You need to google first, if you have "It's urgent please" mentioned in your question.
Wink | ;-)

_AnShUmAn_

Re: string concatenation using pointer

hrishiS6-May-09 23:41

hrishiS

6-May-09 23:41

sorry, But I really didnot get that

-----------------------------
I am a beginner

Re: string concatenation using pointer

Divyang Mithaiwala6-May-09 23:45

Divyang Mithaiwala

6-May-09 23:45

When I was posted I haven't seen your clarification that you are facing run time error (due to no refresh page).

So, If you have taken variable as char temp[10]; and try to execute
*temp++ = *a++;
it will give you compile time error.

Do not trust a computer...
Always check what computer is doing

regards,
Divyang Mithaiwala
Software Engineer

Re: string concatenation using pointer

Fatbuddha 17-May-09 0:00

Fatbuddha 1

7-May-09 0:00

I haven't tested that nor tried something similar, but I think that the hole think wont give you the right result anyway.
By incrementing the char * temp it jumps to the next position and you will lose the previous position, don't you?
So if you really want to do something like that you should have a pointer to the first position of temp (I guess).
So why not simply allocate mem for temp and then do a memcpy with a and b? Given memcpy temp and for b &temp[2] for example.

I hope this will do the trick, but I am just guessing.

Cheers

You have the thought that modern physics just relay on assumptions, that somehow depends on a smile of a cat, which isn’t there.( Albert Einstein)

convert delphi to c++ builder

raj15766-May-09 22:49

raj1576

6-May-09 22:49

I have delphi application .I am trying to convert it into c++ builder

this is my delphi function
function TClipCollection.GetItem(Index: Integer): TClipItem;
begin
Result := inherited Items[Index] as TClipItem;
end;

and this is my builder function
TClipItem TClipCollection::*GetItem(int Index)
{
// Result := inherited Items[Index] as TClipItem;
how i convert this line
}

Re: convert delphi to c++ builder

Stuart Dootson6-May-09 23:53

Stuart Dootson

6-May-09 23:53

Probably something like

TClipItem* TClipCollection::GetItem(int Index)
{
// Result := inherited Items[Index] as TClipItem;
   return (TClipItem*)Items[Index];
}

You need to be sure that the array indices are consistent between Delphi and C++ (C++ array indices start at zero - do Delphi array indices do the same?).

Java, Basic, who cares - it's all a bunch of tree-hugging hippy cr*p

Re: convert delphi to c++ builder

raj15767-May-09 0:45

raj1576

7-May-09 0:45

thanks Stuart Dootson

but i am now getting error

E2451 Undefined symbol 'Items'

where as i defined the property in the TClipCollection class

__property TClipItem *Items[int Index] = { read=GetItem, write=SetItem};

for more details my class like this

class TClipCollection : public TCollection
{
private:
TClipItem *GetItem(int Index);
void SetItem(int Index,TClipItem *Value);

public:

TClipCollection();
__property TClipItem *Items[int Index] = { read=GetItem, write=SetItem};
TClipItem Add();
TClipCollectionEnumerator GetEnumerator();

};

Re: convert delphi to c++ builder

Stuart Dootson7-May-09 1:06

Stuart Dootson

7-May-09 1:06

How are you using Items? It looks to me like the compiler and linker are seeing Items as a global symbol (i.e. not a class member).

Java, Basic, who cares - it's all a bunch of tree-hugging hippy cr*p

Re: convert delphi to c++ builder

raj15767-May-09 1:12

raj1576

7-May-09 1:12

but in delphi it is used

delphi code is this

TClipCollection = class(TCollection)
private
function GetItem(Index: Integer): TClipItem;
procedure SetItem(Index: Integer; const Value: TClipItem);
public
constructor Create;
property Items[Index: Integer]: TClipItem read GetItem write SetItem; default;
function Add: TClipItem;
function GetEnumerator: TClipCollectionEnumerator;
end;

you r right and when i mke the constructor of this class then i got also error
E2251 Cannot find default constructor to initialize base class 'TCollection'

then what i do for this

Re: convert delphi to c++ builder

Stuart Dootson7-May-09 1:37

Stuart Dootson

7-May-09 1:37

rajeshkumarrajput wrote:
but in delphi it is used

Delphi is a different language than C++ - it has different rules - and anyway, I asked you how Items was used in your code - it's the use of something called Items, not the definition that's causing that error.

I suspect your GetItem/SetItem code is overriding the relevant property accessors from TCollection, so you probably need something like:

TClipItem* TClipCollection::GetItem(int index)
{
   return (TClipItem*)(((TCollection*)this)->Items[index]);
}

rajeshkumarrajput wrote:
E2251 Cannot find default constructor to initialize base class 'TCollection'

That'll be because TCollection has no default constructors - look at the documentation (C++ Builder has documentation, I presume?) and work out which constructor you should be using.

Java, Basic, who cares - it's all a bunch of tree-hugging hippy cr*p

Re: convert delphi to c++ builder

raj15767-May-09 1:47

raj1576

7-May-09 1:47

now i am getting the error

E2297 'this' can only be used within a member function

can i send my code to solve the problem ?

Re: convert delphi to c++ builder

Stuart Dootson7-May-09 1:53

Stuart Dootson

7-May-09 1:53

I'd suggest you might want to learn C++ instead - that'll be more use in the long run.

Java, Basic, who cares - it's all a bunch of tree-hugging hippy cr*p

Re: convert delphi to c++ builder

raj15767-May-09 1:56

raj1576

7-May-09 1:56

thanks Stuart Dootson
for help

C++ Template question

rrrado6-May-09 22:48

rrrado

6-May-09 22:48

I need to crate template class which will be generic parent of more classes containing data. Each child class defines something like item ID (different name in each class, but always int) and I need to let parent class know it's name to be able to make some operations on that.

This is pseudocode:

template <class T, ???XXX > class DRecord
{
    void DoReset() {  ((T*)this) ->   XXX = 0; }  // accessing the ID
}


class A : public DRecord<A, ???A_XXX >
{
   int A_XXX;
}

XXX is template param I need to define and use some way. I've tried to use member pointers but it didn't compile. Is it possible to define member of child class as parameter into parent class? In moment of parsing the template the member variable is not declared yet, so I'm not sure whether is it possible.
Thank you.

Re: C++ Template question

CPallini6-May-09 22:55

CPallini

6-May-09 22:55

Why do you want to do that?
Could just use polimorphism, couldn't you?
Smile | :)

Re: C++ Template question

rrrado6-May-09 23:13

rrrado

6-May-09 23:13

I'm creating some database wrapper, it maps tables to classes (or structures). There are some common operations I need to do on primary keys, but each table is using different PK names. I want to code common operations only once (using templates, not preprocessor macros unless necessary) and don't want to use virtual functions (it should be theoretically possible, but I don't know whether C++ templates are powerful enough for this).
It is also interesting problem for me since I'm not template expert and I'd like to learn Smile | :)

Re: C++ Template question

CPallini6-May-09 23:19

CPallini

6-May-09 23:19

rrrado wrote:
and don't want to use virtual functions

Why don't you (you know base classes practically imply this... Roll eyes | :rolleyes:

Re: C++ Template question

rrrado6-May-09 23:37

rrrado

6-May-09 23:37

Because it is not necessary to use virtual tables just to make simple job Smile | :)

Just for one function <pre>virtual int& GetID();</pre> There are more ways how to do this but I'd like to use clean solution.
I have solution with templates for this but it is using extra class and multiple inheritance so I don't like it.
This could be useful for me also in future for different purposes so I'd like to know Smile | :)

Re: C++ Template question

CPallini6-May-09 23:49

CPallini

6-May-09 23:49

rrrado wrote:
Because it is not necessary to use virtual tables just to make simple job Smile Just for one function
virtual int& GetID();

Since this is your point of view, why do you ask for a 'clean solution'? Roll eyes | :rolleyes:

Re: C++ Template question

Stuart Dootson6-May-09 23:49

Stuart Dootson

6-May-09 23:49

How about just presuming the existence of accessor functions in the parent - I've defined a macro to help reduce the amount of typing:

template <class T> class DRecord
{
    void DoReset() {  static_cast<T*>(this)->SetID(0); }  // accessing the ID
};

#define DEFINE_ID_FIELD(ID_NAME) \
   int NAME;
   void SetID(int value) { NAME = value; }
   int GetID(int value) const { return NAME; }

class A : public DRecord<A>
{
   DEFINE_ID_FIELD(A_XXX)
};

As an aside - are you aware of the OLE DB consumer templates[^] - they're templated database wrappers...

Java, Basic, who cares - it's all a bunch of tree-hugging hippy cr*p

Re: C++ Template question

rrrado7-May-09 0:42

rrrado

7-May-09 0:42

Thank you for idea, I was thinking about it and haven't realized that I don't need virtual accessors for this unless I saw your code.
I don't know OLE DB templates, thank you for tip. I'm using sqlite so I guess I cannot use them but maybe there will be some good point in their architecture.

Re: C++ Template question

Stuart Dootson7-May-09 0:46

Stuart Dootson

7-May-09 0:46

rrrado wrote:
I don't know OLE DB templates, thank you for tip. I'm using sqlite so I guess I cannot use them...

I wouldn't bet on it - OLE DB Provider for SQLite[^]

Java, Basic, who cares - it's all a bunch of tree-hugging hippy cr*p

Please help me!! it's urgent!!

erenakman6-May-09 21:29

erenakman

6-May-09 21:29

i'm in an exam. and that's the question. i'vw 2 hours to answer it. thank you.

1. Write a class shape with a constructor that takes no parameters and outputs the message created a shape. The class should have two data members, area and perimeter. Write a main function to test the class by creating an object of the class shape.

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