This macro fills the buffer with the text of the indexed item. It returns the length of the text.

#define INCL_WINWINDOWMGR /* Or use INCL_WIN, INCL_PM, */
#include <os2.h>

HWND     hwndLbox;  /*  List box handle. */
SHORT    index;     /*  Index of the listbox item. */
PSZ      psz;       /*  Pointer to a null terminated string. */
SHORT    cchMax;    /*  Maximum number of characters allocated to the string. */
LONG     lRetTxtL;  /*  Actual text length copied. */

lRetTxtL = WinQueryLboxItemText(hwndLbox,
             index, psz, cchMax);