[RESOLVED] ListBox control

I have a simple diaglog app (MFC) that is calcualting cost based on two listbox controls. However if one or both items are not selected I get an assertion error, "Expression:nLength>=0". I would like to prompt the user if he forgets to select an item in each list but I can't figure out how to do it. I tried to look at the CList member functions but don't know which one

the code below is how I assign the item selected in the listbox to a CEdit control to show the user what he selected.
m_Home.GetText(m_Home.GetCurSel(), m_Hsel);

Any help would be appreciated!

Check the value of GetCurSel before you try to use it for anything. Display an error if its value is LB_ERR (-1).

if (m_Home.GetCurSel()== LB_ERR) {....}

still getting same error but thanks for the advice anyways.

Quote:

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Originally Posted by Zouris

if (m_Home.GetCurSel()== LB_ERR) {....}

still getting same error but thanks for the advice anyways.

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That doesn't really tell anybody anything. What's in the ... ? Based on the very limited information and code you showed, I gave you the correct solution. Any more help will require more input from you.

The assertion error occurrs immediately. There is no cursor to get since I'm not selecting anything from the listBox. It seems like I need to initialize something in the OnInitDiag(Void).

if (m_Home.GetCurSel()== LB_ERR) {AfxMessageBox("error");}

I appreciate your help!

I'm pretty sure I could help you more if you'd post relevant code, but for some reason you seem to be keeping the details to yourself, so good luck.

Did you ever read what that "Assertion failed..." wrote?
Did you press the Retry button?

Really there is not much more code then what I'm showing you?


Bool CHomePrices2011Dlg::OnInitDialog;

I add the following code
... Intialize the Clist selection (there are more selections I'm showing just one)
m_Home.AddString(L"Baltimore");
m_Away.AddString(L"Baltimore");

// I create a simple structure and initialize values

BAL.def=10;BAL.off=13;BAL.tot=BAL.def+BAL.off;

return TRUE; // return TRUE unless you set the focus to a control

;


void CHomePrices2011Dlg::OnBnClickedCompute()
{


double homeT awayT;
homeT =0;
awayT =0;

m_Home.GetText(m_Home.GetCurSel(), m_Hsel);
m_Away.GetText(m_Away.GetCurSel(), m_Asel);

if (m_Hsel=="Baltimore"){homeT=BAL.def+BAL.off+BAL.tot-6;}

if (m_Asel=="Baltimore"){awayT=BAL.def+BAL.off+BAL.tot;}



m_cost = (homeT-awayT)/3000;

UpdateData(FALSE);

}

Dear Zouris,
being in the CG since Mar 2002 and having posted here 36 posts don't still know how to use Code tags? :confused:
Besides, your manner of code writing is very bad for the people who would try to read/understand your code: why do you write more than one command/instruction/assignment in the same line? :confused:
Why don't you provide the minimal necessary info about variable types you use in your code snippets?

And finally: what does your last code snippets have to do with the error (assertion fault) you have? :confused:

Please be professional and keep your negative comments to yourself. I'm not here to get your approval on my programming styles. Also, I did indicate what the assertion error was in my first post.

My inclination is that I'm not initializing something correctly and I thought there was a simple command.

Where are you testing GetCurSel for LB_ERR?

You can't call GetText if GetCurSel is LB_ERR. From what you wrote in the first post that's your problem, and Victor is right. Please use code tags, and it's not in your best interests to get snippy with senior members here if you want continued help.

Quote:

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Originally Posted by Zouris

Please be professional and keep your negative comments to yourself. I'm not here to get your approval on my programming styles

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Well, if you really need help but your "programming styles" prevent people to read/understand your code/probllems then I will recommend you to change your styles. Seriously! :cool:

Quote:

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Originally Posted by Zouris

Also, I did indicate what the assertion error was in my first post.

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So again:
Did you read all the text on the"Assertion failed..." dialog, something like:

Quote:

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Debug Assertion Failed
Program <...>.exe
File <,,,>
Line <,,,>
Expression <...>.
For info on how your program can cause an assertion
failure, see the visual C++ documentation on asserts
Press Retry to debug the application

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Did you press the Retry button?
In what file did the assertion fail?

makes sure you are selecting one of the item in the Listbox before calling :

Code:

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m_Home.GetText(m_Home.GetCurSel(), m_Hsel);

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check if your m_Home.GetCurSel() is returning "-1" ( means none of the items are selected ) then just proceed further.. ; dont call GetText...

Quote:

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if (m_Home.GetCurSel()== LB_ERR) {AfxMessageBox("error");}

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You must merely interrupt button handler in case of violated/unacceptable conditions.

Code:

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void SomeDlgClass::OnSomeButton()
{
    if (m_Home.GetCurSel()== LB_ERR)
    {
        AfxMessageBox("error");
        return;
    }

. . . // normal processing
}

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Thank You Igor!!! That was exactly the problem.

Quote:

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Originally Posted by Zouris

Thank You Igor!!! That was exactly the problem.

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Isn't that what I told you yesterday. Sheesh.:rolleyes:

Almost 100&#37; of functions used return some sort of value...these usually indicate success or failure...these return values should ALWAYS be checked else you are assuming the function was successful...this is not a good thing..

Also you might want to lookup info on Hungarian notation...I'm sure there are many out there that don't use (or agree with) this but when you do programs with 100K++ lines of code it will make things much easier to understand the code after not working with it for a while...plus if you get into a group programming enviroment it will make things easier on all if naming consistency is used.

ed: All of the more senior members here are volunteers helping people with their programming problem(s) and have good intentions to resolve them as fast as possible...sometimes this requires faith on the part of the requestor to give the member the info they have asked for and not what the requesting party thinks they need. There are senior members here that dedicate a good portion of their day helping people here and have well in excess of 10,000 post...most of them being answers to posted questions.

We also understand that you are having a problem that needs to be solved RIGHT NOW and that can/will be stressful...but you should also understand that it might take a little time to get an answer since the member with the solution might not be in the same time zone, country or even hemisphere as you...Of course that is just my opinion, I could be wrong.

Code:

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int iRetValue = LB_ERR;

iRetValue = m_Home.GetCurSel();
//  Hungarian notation for the above
//  iRetValue = m_lbHome.GetCurSel();

if(iRetValue != LB_ERR)
{
  m_Home.GetText(iRetValue, m_Hsel);
  //  Hungarian notation for the above
  //  m_lbHome.GetText(iRetValue, m_csHsel);
  //  m_lbHome is a member variable to a ListBox
  //  m_csHsel is a member variable to a CString
}
else
{
  AfxMessageBox("Item Not Selected for Hsel");
  //  if this is in a function the return your own error code
  //  with something like return(FALSE)/return(TRUE)
  //  and check all return values even from you own functions.
  return;
}

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Its obvious, I'm not an advanced programmer as you guys are so I apologize for my lack of knowledge. I'm primarily a SAS programmer so I tend to program what makes sense to me although I understand when requesting help its difficult for the person trying to help you debug your code.

Again, thanks to everybody's help and I apolgize if I offended anybody due to improper programming etiquette. Code Guru has always been a valuable resource and you guys go out of your way to help people which is pretty cool!!!