How I retrieve the LPARAM value of a ctreectrl MFC

Question

0.00/5 (No votes)

See more:

I have a Tree Control where each node is associated with a LPARAM value. On a particular button click event I want to retrieve the LPARAM value. The below given code is executed more than once. so when i trying to retrieve the LPARAM value for the initial values its a garbage value.

What I have tried:

strTemp.Format(_T("%s %f %s %f"), _T("Length: "), fLength, _T("-->"), fCXLength);
m_strParamval = _T("LENG") + CXString::Format(_T("%d"), m_nMatID);
LPCTSTR pszParamVal = m_strParamval;

HTREEITEM hMatChild = m_cTreeCtrl.InsertItem(TVIF_TEXT | TVIF_IMAGE | TVIF_SELECTEDIMAGE | TVIF_PARAM,strTemp, 0, 0, 0, 0, (LPARAM)pszParamVal, m_hMatNode, TVI_LAST);

this is the coed for retrieving:

TVITEMEX item1;
item1.mask = TVIF_PARAM;
item1.hItem = m_hMatTest;


TreeView_GetItem(m_cTreeCtrl, &item1);
CString strPath1 = (LPCTSTR)item1.lParam;

Posted 20-Apr-17 23:12pm

Member 12677926

Updated 21-Apr-17 0:53am

Add a Solution

1 solution

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Jochen Arndt · Accepted Answer · 2017-04-21T00:53:00

This will never work as expected.

You are storing the string in m_strParamval. This string will be updated whenever you insert a new item. So you would always get the string for the last added item.

But more important, the LPARAM values might not point to a valid string anymore. m_strParamval is of type CString which might allocate new memory when assigning a new string that is larger than the existing content. Then the pointer returned by CString::GetString() (which is used when assigning a CString to a LPCTSTR) is not valid anymore.

If you want to store individual strings for each item you have to use allocated memory for each item and free that when items are removed and the tree is destroyed.
Example:

CString strParamval = _T("LENG") + CXString::Format(_T("%d"), m_nMatID);
TCHAR *pszParamVal = new TCHAR[strParamval.GetLength()];
_tcscpy(pszParamVal, strParamval.GetString());

Again: When doing so, don't forget to delete the memory when deleting items or destroying the tree control.