Question

A question on ListView_SetItemText macro for setting text of items in ListView Windows control.
Why does the following code works (in a sense that the text is displayed in the ListView)

std::string strNumber = NumberToString(number);
ListView_SetItemText( hListView, iItemIndex, iSubitemIndex, (LPSTR)strNumber.c_str() );

while a direct call doesn’t

ListView_SetItemText( hListView, iItemIndex, iSubitemIndex, (LPSTR)NumberToString(number).c_str() );

where

std::string NumberToString ( double Number ) 
{ 
  std::ostringstream ss; 
  ss << Number; 
  return ss.str(); 
}

Many thanks

Answer 1

Here’s the macro definition (in commctrl.h):

#define ListView_SetItemText(w,i,iS,s) \
{ \
    LV_ITEM _lvi;\
    _lvi.iSubItem=iS;\
    _lvi.pszText=s;\
    SNDMSG((w),LVM_SETITEMTEXT,i,(LPARAM)(LV_ITEM*)&_lvi);\
}

This expands to:

    ...
    _lvi.pszText=(LPSTR)NumberToString(number).c_str();
    SNDMSG((hListView),LVM_SETITEMTEXT,iItemIndex,(LPARAM)(LV_ITEM*)&_lvi);
}

The NumberToString function returns a temporary std::string, which is deleted before the SNDMSG call. So _lvi.pszText points to thin air. (Your code would be perfectly safe if ListView_SetItemText were a genuine function call.)