C / C++ / MFC

Re: Difference between visual c++ and visual c++.net

8-Sep-05 7:29

Ming Luo wrote:
Somebody told me that application developed in .net framework is compiled in-time. So it's slow. But application developed in c++ is compiled, it's quicker.

This is only partly correct. Once the .Net framework has been loaded, the differences in speed are negligible.

Ming Luo wrote:
So could anybody give me an idea what's the difference between v++ and c++.net please???

See here, here, and here.

Ming Luo wrote:
Another question is that if I make an application in c++ using mysql as my database. How can I make a connection to the source database please???

If you are using MFC, check out the CRecordset and CDatabase classes. Otherwise, you can use the ODBC API directly.

"One must learn from the bite of the fire to leave it alone." - Native American Proverb

Christian Graus8-Sep-05 12:27

Christian Graus

8-Sep-05 12:27

A C++ app is only 'slower' if you use managed c++, otherwise, it's the same as any C++ compiler.

Ming Luo wrote:
And what's the exactly meaning of the win32 project? What's the difference between win32 project and the windows form application project???

Windows Forms is managed C++, it's slower, and more complex to use in C++. Win32 is a console app, or a non MFC C++ app. An MFC app is probably what you want.

Christian Graus - Microsoft MVP - C++

Re: Difference between visual c++ and visual c++.net

Ming Luo8-Sep-05 21:45

Ming Luo

8-Sep-05 21:45

I am a quite new C++ learner. Could you tell me what's the exactly meaning of managed C++ please? And how can I avoid using managed C++???
Thanks

Asura

Re: Difference between visual c++ and visual c++.net

Christian Graus11-Sep-05 11:15

Christian Graus

11-Sep-05 11:15

Managed c++ is c++ with added keywords to use the .NET framework. If you create MFC applications with the form wizard, they should be unmanaged by default. In any case, if you don't use the .NET framework, I doubt that having a MC++ app will hurt, it will just sit there, unused.

Christian Graus - Microsoft MVP - C++

MS Hierarchical FlexGrid

pjhenry12168-Sep-05 5:31

pjhenry1216

8-Sep-05 5:31

I'm using MS Hierarchical FlexGrid to display hierarchical data from a database in a grid. As of now, I can't find out how to do that. I'm using Microsoft Visual C++ .NET 2003. I want to display data from two tables. One table has primary information, and the second table has multiple records for each record in the primary table. I'd like to display just the primary information and just let the user highlight a record to see what records in the second table belong to it. If anybody knows how to use the MSHFlexGrid (mshflxgrd.ocx... as opposed to the non-hierarchical one msflxgrd.ocx) and could offer any help, that'd be appreciated. Or if anybody knows how to solve this problem without mshflexgrid, that'd be great as well.

how to accessing std:map (index)th element

yccheok8-Sep-05 4:42

yccheok

8-Sep-05 4:42

May I know how I can access map by index just like I access vector by index?

cout<< "This is the 10th element (0 based) in my vector = "<< myVector[10];

For map, when I wish to access the 10th element (0 based), I would do the following:

map<char *,="" int="">::iterator curr, end;

end = myMap.end();

curr = myMap.begin();

for(int i=0; i<10; i++) {

curr++;

}

cout<< "This is the 10th element (0 based) in my map = "<< myMap->second;

I was wondering whether is there any better way other than having to loop through all the items? For example:

/* The following code is just a wish, it is not valid. */
cout<< "This is the 10th element (0 based) in my vector = "<< myMap.getItemByIndex(10);

Thank you.

cheok

Re: how to accessing std:map (index)th element

Maximilien8-Sep-05 5:54

Maximilien

8-Sep-05 5:54

std::map is not a random access container, you cannot access a item directly like you can do for std::vector.

Me think that accessing an indexed element of a map ( i.e. the 10th element ) is not usefull.

AFAIK, looping maps like you do will work.

Maximilien Lincourt
Your Head A Splode - Strong Bad

Re: how to accessing std:map (index)th element

garbash8-Sep-05 7:06

garbash

8-Sep-05 7:06

You can but there could be a high price to pay performance-wise depending our the std::map implementation you are using:

#include <map>
#include <string>
#include <iostream>
void main( )
{
typedef std::map<int, std::string> Numbers;
Numbers n;
n.insert(Numbers::value_type(1,"one"));
n.insert(Numbers::value_type(2,"two"));
n.insert(Numbers::value_type(3,"three"));

Numbers::iterator iCurrent = n.begin();
// You can use the 0-based index of the element to access
// This is not an efficient way to access element of map
// and there is no out-of-boundary validation. You have
// been warned!
std::advance(iCurrent, 1);

std::cout << (iCurrent->second).c_str() << std::endl;
}

A better approach would probably be to store your data in a std::vector, the sort it with std::sort. This way you can use std::find to achieve logarithmic access time as per std::map or instant access time with std::vector's operator[].

Good luck,

g.

Re: how to accessing std:map (index)th element

Bob Stanneveld8-Sep-05 10:42

Bob Stanneveld

8-Sep-05 10:42

Hello,

the std::map container is not designed for array indexed access. If you need this, you probably chose the wrong container.

You can however copy the contents of the map to a vector and access it from there:

std::vector<int> vec;
vec.insert(yourmap.begin(), yourmap.end());
int i = vec[1];

Behind every great black man...
... is the police. - Conspiracy brother

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Edit a record in a DB table opened with ODBC

sirtimid8-Sep-05 4:32

sirtimid

8-Sep-05 4:32

Itr to edit a record of a table which it has fields of type float.
When these fields have decimals the update cannot be done. But when they are without decimals the update is successful.
Does anyone know how can I update the record even if it has fields with decimals?

Thanks in Advance

Re: Edit a record in a DB table opened with ODBC

David Crow8-Sep-05 4:35

Re: Edit a record in a DB table opened with ODBC

8-Sep-05 4:35

Without seeing a relevant code snippet, it's hard to say what you are doing wrong.

"One must learn from the bite of the fire to leave it alone." - Native American Proverb

sirtimid8-Sep-05 4:51

sirtimid

8-Sep-05 4:51

double value=15.1

TableSet->Open();
TableSet->MoveFirst();
while(!TableSet->IsEOF()) {
if(TableSet->m_field1 == id) {
TableSet->Edit();
TableSet->m_field2 += value;
TableSet->Update();
} else {
TableSet->MoveNext();
}
}

When TableSet->m_field2, which is of type float, has decimals the update return error.
When it does not have decimals no error occurs.
Any idea?

Re: Edit a record in a DB table opened with ODBC

David Crow8-Sep-05 5:53

8-Sep-05 5:53

sirtimid wrote:
...the update return error.

And what would that error be?

What does the DoFieldExchange() method look like for the CRecordset-derived class?

Is the corresponding field in the database table a floating-point type?

"One must learn from the bite of the fire to leave it alone." - Native American Proverb

Redefinition

Babto8-Sep-05 4:13

Babto

8-Sep-05 4:13

Is it correct in anyway to declare a same variable (variable type and name same) multiple times in Visual C++ code of single block ?

For example,

void Function( int i, int j )
{

HRESULT hr = E_FAIL;
.
.
.
HRESULT hr = CComObject::GetInterface(...);
.
.
}

Appreciate answers and suggestions. Thanks in advance.

Cedric Moonen8-Sep-05 4:17

Cedric Moonen

8-Sep-05 4:17

No you can't. Otherwise the compiler has no clue of which instance you are working with.

-- modified at 10:19 Thursday 8th September, 2005

Seing your post, a thing what you can do is simply not redifine your variable:

HRESULT hRes = E_FAIL;<br />
....<br />
<br />
hRes = ...<br />

Babto8-Sep-05 5:41

Babto

8-Sep-05 5:41

Is there any facility in Visual C++ to satisfy the compiler by specifying compile (or build) options or MACRO definitions to accept redeclaration of variable of similar type in same block ?

Maximilien8-Sep-05 5:59

Maximilien

8-Sep-05 5:59

Why would you want ot redeclare the same variable in the same logical code block ?

can't you declare it at the top of the block, and assign ( and re-assign ) values as needed ?

...
int iValue;
...
iValue = 4;

...
iValue = 10;
...

maybe your variable type does not support an = operator ( if it's a class ), you should define one, or do something like :

MyClass* pMyClass; // class with a constructor that accept an int value.

pMyClass = new MyClass( 5 );
...

delete pMyClass;

pMyClass = new MyClass( 10 );
...

delete pMyClass;

Maximilien Lincourt
Your Head A Splode - Strong Bad

David Crow8-Sep-05 4:32

Problem with worker thread

8-Sep-05 4:32

It would only be syntactically correct if you did it thusly:

void Function( int i, int j )
{
    HRESULT hr = E_FAIL;
    .
    .
    {
        HRESULT hr = CComObject::GetInterface(...);
    }
    .
    .
}

"One must learn from the bite of the fire to leave it alone." - Native American Proverb

ashtwin8-Sep-05 4:06

ashtwin

8-Sep-05 4:06

Hi, i am using multithreading in my application. I want to use MFC object(view and MainFrame object) in my worker thread. Can anybody tell how to do this.
Thanks.

David Crow8-Sep-05 4:34

8-Sep-05 4:34

What do you mean by "use?" Worker threads (i.e., those without a message pump) should not interact with UI components other than to post a message to the component's owner. The owner is therefore responsible for updating the UI component.

"One must learn from the bite of the fire to leave it alone." - Native American Proverb

Marc Soleda8-Sep-05 4:37

Marc Soleda

8-Sep-05 4:37

From within your worker thread you have a handle to its parent. Using this handle you'll be able to use/interact with this MFC object.

Marc Soleda.

... she said you are the perfect stranger she said baby let's keep it like this... Tunnel of Love, Dire Straits.

-- modified at 10:46 Thursday 8th September, 2005

Jim Howard8-Sep-05 12:54

Jim Howard

8-Sep-05 12:54

No, you don't want to use your view and mainframe objects in a worker thread. That will cause a disaster of biblical proportions. Those objects belong to the GUI thread.

The way your work thread will interact with the GUI is by passing the thread a pointer to the view or mainframe window, and then posting messages to this window.

Go to flounder.com and read Dr Newcomber's articles on threading.