Thread: Somethings wrong...

Hey, wondered if someone could give me a bit of wisdom as to why my program compiles fine but crashes during use.

Its just a simple program with two edit controls. I enter text into edit control A and press the "submit" button and it reappears in edit control B. This works fine for string lengths up to 10 characters...why doesn't it work for longer strings?

It either stops responding, or just closes.

Code:

 
         switch (wParam)                      
             {                          
                  case SUBMIT:
                              {
                              LPSTR text;
                              DWORD nochars =GetWindowTextLength(EntryBoxA);
                              if (nochars != NULL) 
                                 {
                                      GetWindowText(EntryBoxA, text,nochars+1);
                                      SetWindowText(EntryBoxB, text);                                  }
                              else
                                 {
                                      MessageBox(hwnd, "No Window Text Length!", "None", MB_OK | MB_ICONINFORMATION);
                                 }
                             } 
                             break;
                   default:
                             break;
                      }

You are creating a pointer to where you want the text to go, but not the actual storage space.

When you say DWORD nochars you are creating a 4 byte entity that can hold a value. When you say LPSTR text, you are creating a 4 byte pointer that points to what? Nothing!

You need to create a char array and pass that to Get/Set WindowText().

>>LPSTR text;<<

Allocate memory with malloc or new (and free or delete[] it after use, of course) for the string pointer before using it . Alternatively, if you know that the string will not exceed a certain length then just declare a string (TCHAR) array of that size (+1 to include '\0' ).For example, using new

Code:

TCHAR *text;
DWORD nochars =GetWindowTextLength(EntryBoxA);
if (nochars != NULL) 
  {
  text=new TCHAR[nochars+1];
  GetWindowText(EntryBoxA, text,nochars); 
  SetWindowText(EntryBoxB, text);     
  delete[] text;
  }

edit: biffed by adrianxw.