Re: how can i switch between programs - C / C++ / MFC Discussion Boards

Re: newbie question about strcpy and pointers

SanShou24-Jul-02 6:35

24-Jul-02 6:35

Function scope would be a good place to start.

You wrote the following function...

ns wrote:
MyFunc(char* abc)
{
char* val = "aaa";
abc = val;
}

It has to do with both pointers and with memory allocation.

First by reassigning pointers such as:
ns wrote:
abc = val

you are now pointing the incoming character pointer to the same memory as 'val'. Remember though, there are two things going on here.

First: Function scope does not allow the changes to abc to be reflected to the caller. The actual value that is passed in as 'abc' is not stored at the same location as the orginal 'abc'. The following code trys to demonstrate the timing and values of the pointers.

Main
{
char* abc = "Home";
// abc = memory addr = 0x00000a, *abc (contents of abc or memory 0x0000a is "H")
MyFunc(abc);
// FUNCTION EMBEDDED TO DEMOSTRATE TIMING
MyFunc(char* abc)
{
char* val = "aaa";
// val = memory addr = 0x01000, *val (contents of val) is "a"
// abc = memory addr = 0x0000a, *val (contes of abc) is "H"
abc = val;
// val = memory addr = 0x01000, *val (contents of val) is "a"
// abc = memory addr = 0x01000, *val (contes of abc) is "a"
}
// abc is reset by the stack back to the original. This is function scope.
// abc = memory addr = 0x00000a, *abc (contents of abc or memory 0x0000a is "H")
}

Second even if you corrected this to pass a pointer to a pointer:
(pass in a pointer to the pointer where the memory for the string is)
pabc->abc->"The string"
pabc = 0x02000 which is the memory addr of abc
abc = 0x0000a which is the memory where the string resides.

MyFunc(char** pabc)
{
char* val = "aaa";
*pabc = val;
}

It changes to pabc->val->"aaa" and pabc->abc->"aaa" while still in the function call. However remember that the function releases its stack values when it exits so we cannot guarantee that someone else will not write to that memory. So the memory that was at the orginal abc pointer is still allocated, but the memory at val or the new abc is released and can be unexpected garbage.

When you use:
ns wrote:
strcpy(abc,val)
you are physically reassigning memory from one place to another. You are retaining the orginal area in memory for each string and moving the contents. A very simple rewrite of strcpy is this:

strcpy(char* a, char* b)
{
// look for an ending null termination
while (*b != '0')
{
*a++ = *b++;
}
}

Notice it is changing the value of what it is pointing to and not where it is pointing. This allows it to move or copy the string in to memory that exists and across the stack reset from functions. Also notice I can increment the pointers and not affect the values that were passed in because of function scope.

Just to let you know I hate text and wish I could draw some pictures, but I tried my best to illustrate the point in English. Let me know if you need more clarification or maybe someone else can clarify what I said.

Brian

If you start a fire for a man, he will be warm for a day. If you start that same man on fire, he will be warm for the rest of his life.

Re: newbie question about strcpy and pointers

Philippe Mori24-Jul-02 8:03

Philippe Mori

24-Jul-02 8:03

Generally, it is better to uses std::string class instead of using raw pointers. Far more easier to uses and less error-prone.

And for the rest, many people have already answer the question.

Philippe Mori

TROLL QUESTION

troll-124-Jul-02 5:32

troll-1

24-Jul-02 5:32

Even though MS is the most resourceful software comapny in the world and hires the most accadmecally qualified and supposedly the most intelligent developerers, it does not produce innovative ,imaginative or quality software on a consistant basis. Instesd it produces buggy software tested on it's smug users through a a number of versions. Not that MS software isn't good or the company is evil, but with its awesome financial resources, though the company could do better,it doesnt. Why?

Re: TROLL QUESTION

Tomasz Sowinski24-Jul-02 5:46

Tomasz Sowinski

24-Jul-02 5:46

troll-1 wrote:
Why?

Because they didn't hire you? Anyway, VC board isn't a place to ask this kind of question. Go to lounge or soapbox instead.

Tomasz Sowinski -- http://www.shooltz.com

- It's for protection
- Protection from what? Zee Germans?

Dialog Bar Docking

BishGada24-Jul-02 5:30

BishGada

24-Jul-02 5:30

Hello,
I'm here to ask what message is sent when the dialog bar is moved to a position where it can be docked, because I want to change its appearance and size depending on the side it gonna be docked.

thanks,
Guy.

how can i switch between programs

f.o.b24-Jul-02 5:30

f.o.b

24-Jul-02 5:30

Hi,

i want to write two programs, which are able to switch to the other program (if they are running). Both programs have a button. If you press this button:

1. The other program is launching if it is not running.
2. If the other program is running (multiple instance possible), the window of one of these instances should be pop to the front of the desktop.

Has anybody an idea?

Ciao

f.o.b

Re: how can i switch between programs

Paul M Watt24-Jul-02 7:06

Paul M Watt

24-Jul-02 7:06

The most important thing is to get a handle to teh window in the other application. You can do this with GetWindow. You may have to do some searching through all of the windows, but you will be able to find the window in the other app with this API.

Next you can call SetForegroundWindow on that window handle. This will bring that window to teh foreground and give it keyborad access.

Build a man a fire, and he will be warm for a day
Light a man on fire, and he will be warm for the rest of his life!

Re: how can i switch between programs

Scott H. Settlemier24-Jul-02 8:56

Scott H. Settlemier

24-Jul-02 8:56

Do a search for AttachThreadInput in here over the last weeks or so.
There are issues with SetForegroundWindow that must be worked around
for your plan to succeed. (unless you still run Win95 Smile | :)

)

I'm doing something silly - help!

ns24-Jul-02 5:18

24-Jul-02 5:18

I want to get the keyvalue out:

void DLLGetValue(int imageIndex,CString key,char* keyvalue)
{

if (imageIndex == 0)
{
if (key=="abc") value="aa";
if(key=="def")value = "ss";
if (key == "aaa")value = "dd";
}
strcpy(keyvalue, value);
}
and its called like:
std::set<cstring>::iterator it = pDoc->m_keySet.begin();

for (; it != pDoc->m_keySet.end() Wink | ;)

{
char* p = new char[2]; p[0] = p[1] = '\0';

int size=30;

if (size)
{
delete[] p;

p = new char[size + 1];

DLLGetValue(imageIndex,*it,p);
}
When p comes back, its full of garbage. WHat did I do wrong?

Thanks,
ns

Re: I'm doing something silly - help!

Tomasz Sowinski24-Jul-02 5:25

Tomasz Sowinski

24-Jul-02 5:25

From the top of my head - you should have at least three character buffer for "aa", "ss" or "dd" - don't forget about trailing null character. However, why on Earth would one mix these manual, low-level, stinky character operations with STL? Can't you just use string& as keyvalue?

Tomasz Sowinski -- http://www.shooltz.com

- It's for protection
- Protection from what? Zee Germans?

Re: I'm doing something silly - help!

ns24-Jul-02 5:54

24-Jul-02 5:54

Thanks. You are quite right about CString being a better choice, but I'm simulating a DLL that pre-exists and returns a char *, so I had to venture into the not-so-friendly world of char. Eventaully it replaces my fake function.

Thanks again,
ns

- I meant it didnt compile-got it now!!

ns24-Jul-02 5:24

24-Jul-02 5:24

OOps,I meant it didnt run at all, didnt compile errors were like:

C:\Trainer\Train\Train1\Train1View.cpp(796) : error C2440: '=' : cannot convert from 'char [7]' to 'int'
which didnt clue me in to the fact that I had not declared "value" . I'm sure that error was there too, but I didnt see it buried in all the compiler warnings for STL.

It works now.
Thanks,
ns

Re: I'm doing something silly - help!

Ravi Bhavnani24-Jul-02 7:00

Ravi Bhavnani

24-Jul-02 7:00

(I know I'm not answering your question, but...) You should bracket your code within <pre> and </pre> tags in order to preserve the indentation so that it's easy to read. The new formatting buttons that Chris introduced makes it easy to do this.

Thanks,

/ravi

Let's put "civil" back into "civilization"
http://www.ravib.com
ravib@ravib.com

Re: - I meant it didnt compile-got it now!!

Christian Graus24-Jul-02 12:38

Christian Graus

24-Jul-02 12:38

ns wrote:
I'm sure that error was there too, but I didnt see it buried in all the compiler warnings for STL.

You can get rid of those warnings with a pragma.

Christian

come on all you MS suckups, defend your sugar-daddy now. - Chris Losinger - 11/07/2002

Re: - pragma warning.

ns25-Jul-02 1:34

25-Jul-02 1:34

I found this:

#pragma warning(disable:4786)

I included it in every file that had #include <set> in it. I still got warnings - a ton- and all are 4786. I am reading http://www.codeproject.com/vcpp/stl/stl_without_warnings.asp now. Thanks very much for your response,
ns

How to Integrate a version for DLL

Raphael Kindt24-Jul-02 3:26

Raphael Kindt

24-Jul-02 3:26

I want to integrate a version for my DLL... How to do that???
Thanks in advances

Hello World!!! Smile | :)

from Raphaël

Re: How to Integrate a version for DLL

Ravi Bhavnani24-Jul-02 4:50

Ravi Bhavnani

24-Jul-02 4:50

Add a resource script (.rc) file to the project, then select the "Resources" tab within VC++ and add a version resource.

/ravi

Let's put "civil" back into "civilization"
http://www.ravib.com
ravib@ravib.com

need help in c program

Henry soon24-Jul-02 3:14

Henry soon

24-Jul-02 3:14

I was the beginner of the learner c language now meet some proble instead donot how to apply the colour source in my program so hope can u help me? The project that want to apply in the background text and text that hv the colour.
Thank you.

Re: need help in c program

benjymous24-Jul-02 3:56

benjymous

24-Jul-02 3:56

I'm sorry, but I can't understand what you're trying to ask Frown | :(

--
Help me! I'm turning into a grapefruit!

Re: need help in c program

henry soon24-Jul-02 4:02

henry soon

24-Jul-02 4:02

i want ask how to apply the colour in the c language program while we execute the program that colour will appear at the MS-DOS Prompt

Re: need help in c program

henrysoon24-Jul-02 4:04

henrysoon

24-Jul-02 4:04

i need the colour source code and that function how to use i hv try before that with using the #include <graphics.h> to apply the color for my text and text background color but cannot work

Re: need help in c program

benjymous24-Jul-02 4:35

benjymous

24-Jul-02 4:35

To change colours in a console window use SetConsoleTextAttribute

--
Help me! I'm turning into a grapefruit!

Constructors throwing exceptions cont.

tom7624-Jul-02 3:13

tom76

24-Jul-02 3:13

My current code is this

AddPrinterDialog::AddPrinterDialog()
{
try
{
mAddPrinterDialogPointer = new AddPrinterDialog;
}
catch(...)
{
PostMessage( WM_QUIT, 0, 0 );

}
}

BUT what happens if I have an overloaded constructor that initialises data members during construction? My try block won't work will it, as I am using 'new' to implicitly call the default constructor.

How could I change my code so I can construct an object with all data members initialised to ArgumentA that is passed in?

Daniel

Obseve everything, remember more...

Re: Constructors throwing exceptions cont.

Tomasz Sowinski24-Jul-02 3:21

Tomasz Sowinski

24-Jul-02 3:21

I'm not sure what you're after now. Can't you just use right constructor with new?

m_addPrinterDialogPtr = new AddPrinterDialog("doopa", "zoopa", "koopa", NULL, 3.14);

Tomasz Sowinski -- http://www.shooltz.com

- It's for protection
- Protection from what? Zee Germans?

Re: Constructors throwing exceptions cont.

tom7624-Jul-02 4:02

tom76

24-Jul-02 4:02

I've just found that the following puts the aplication into an assertion loop.

// Default constructor<br />
AddPrinterDialog::AddPrinterDialog()<br />
{<br />
    try<br />
    {<br />
        mAddPrinterDialogPointer = new AddPrinterDialog;<br />
    }<br />
    catch(...)<br />
    {<br />
<br />
    }<br />
<br />
}

All I want is some code that has a constructor throwing an exception if it fails. It seems I can't use the current code.

That webpage was interesting, but the code was v.confusing. For example

<br />
// Example 1(a): Constructor function-try-block<br />
//<br />
C::C()<br />
try<br />
  : A ( /*...*/ ) // optional initialization list<br />
  , b_( /*...*/ )<br />
{<br />
}<br />
catch( ... )<br />
{<br />
  // We get here if either A::A() or B::B() throws.<br />
<br />
  // If A::A() succeeds and then B::B() throws, the<br />
  // language guarantees that A::~A() will be called<br />
  // to destroy the already-created A base subobject<br />
  // before control reaches this catch block.<br />
}<br />
<br />

is all very well but what if you're NOT inheriting? Or you don't care about parent classes (say you derived from an MFC class).

All I want is a default constructor throwing an exception. But I have no idea how you test for an object's existence, especially inside the default constructor's body as the object won't have been created yet.

Obseve everything, remember more...

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