GetDlgItemText should always try to NULL terminate the string.

dlls/user/dialog.c

@@ -1295,6 +1295,7 @@ BOOL WINAPI SetDlgItemTextW( HWND hwnd, INT id, LPCWSTR lpString )
  */
 INT WINAPI GetDlgItemTextA( HWND hwnd, INT id, LPSTR str, UINT len )
 {
+    if (str && (len > 0)) str[0] = '\0';
     return (INT)SendDlgItemMessageA( hwnd, id, WM_GETTEXT,
                                          len, (LPARAM)str );
 }
@@ -1305,6 +1306,7 @@ INT WINAPI GetDlgItemTextA( HWND hwnd, INT id, LPSTR str, UINT len )
  */
 INT WINAPI GetDlgItemTextW( HWND hwnd, INT id, LPWSTR str, UINT len )
 {
+    if (str && (len > 0)) str[0] = '\0';
     return (INT)SendDlgItemMessageW( hwnd, id, WM_GETTEXT,
                                          len, (LPARAM)str );
 }

dlls/user/tests/dialog.c

@@ -849,6 +849,18 @@ static void InitialFocusTest (void)
     }
 }
 
+static void test_GetDlgItemText(void)
+{
+    char string[64];
+    BOOL ret;
+
+    strcpy(string, "Overwrite Me");
+    ret = GetDlgItemTextA(NULL, 0, string, sizeof(string)/sizeof(string[0]));
+    ok(!ret, "GetDlgItemText(NULL) shouldn't have succeeded\n");
+
+    ok(string[0] == '\0', "string retrieved using GetDlgItemText should have been NULL terminated\n");
+}
+
 
 START_TEST(dialog)
 {
@@ -860,4 +872,5 @@ START_TEST(dialog)
     IsDialogMessageWTest();
     WM_NEXTDLGCTLTest();
     InitialFocusTest();
+    test_GetDlgItemText();
 }