diff --git a/src/core/ctlr.c b/src/core/ctlr.c
index e692fac..77abdfd 100644
--- a/src/core/ctlr.c
+++ b/src/core/ctlr.c
@@ -318,7 +318,7 @@ static void ctlr_connect(H3270 *hSession, int GNUC_UNUSED(ignored), void GNUC_UN
 	hSession->crm_nattr = 0;
 }
 
-LIB3270_EXPORT int lib3270_get_is_formatted(H3270 *hSession)
+LIB3270_EXPORT int lib3270_get_is_formatted(const H3270 *hSession)
 {
 	if(check_online_session(hSession))
 		return -1;
@@ -389,7 +389,7 @@ LIB3270_EXPORT int lib3270_get_field_len(H3270 *hSession, int baddr)
 	return -(errno = ENODATA);
 }
 
-LIB3270_EXPORT int lib3270_field_addr(H3270 *hSession, int baddr)
+LIB3270_EXPORT int lib3270_field_addr(const H3270 *hSession, int baddr)
 {
 	int sbaddr;
 
@@ -525,11 +525,11 @@ LIB3270_EXPORT int lib3270_get_next_unprotected(H3270 *hSession, int baddr0)
 	return 0;
 }
 
-LIB3270_EXPORT int lib3270_get_is_protected_at(H3270 *h, unsigned int row, unsigned int col) {
-	return lib3270_get_is_protected(h, ((row-1) * h->view.cols) + (col-1));
+LIB3270_EXPORT int lib3270_get_is_protected_at(const H3270 *h, unsigned int row, unsigned int col) {
+	return lib3270_get_is_protected(h, lib3270_translate_to_address(h,row,col));
 }
 
-LIB3270_EXPORT int lib3270_get_is_protected(H3270 *hSession, int baddr)
+LIB3270_EXPORT int lib3270_get_is_protected(const H3270 *hSession, int baddr)
 {
 	FAIL_IF_NOT_ONLINE(hSession);
 
diff --git a/src/core/keyboard/properties.c b/src/core/keyboard/properties.c
index 1e79740..531a84a 100644
--- a/src/core/keyboard/properties.c
+++ b/src/core/keyboard/properties.c
@@ -31,7 +31,7 @@
 #include <lib3270/keyboard.h>
 #include <lib3270/properties.h>
 
-LIB3270_EXPORT LIB3270_KEYBOARD_LOCK_STATE lib3270_get_keyboard_lock_state(H3270 *hSession)
+LIB3270_EXPORT LIB3270_KEYBOARD_LOCK_STATE lib3270_get_keyboard_lock_state(const H3270 *hSession)
 {
 	if(check_online_session(hSession))
 		return LIB3270_KL_NOT_CONNECTED;
@@ -45,7 +45,7 @@ LIB3270_EXPORT int lib3270_set_lock_on_operator_error(H3270 *hSession, int enabl
 	return 0;
 }
 
-int lib3270_get_lock_on_operator_error(H3270 *hSession)
+int lib3270_get_lock_on_operator_error(const H3270 *hSession)
 {
  	return (int) hSession->oerr_lock;
 }
@@ -57,7 +57,7 @@ LIB3270_EXPORT int lib3270_set_unlock_delay(H3270 *hSession, unsigned int delay)
 	return 0;
 }
 
-LIB3270_EXPORT unsigned int lib3270_get_unlock_delay(H3270 *hSession)
+LIB3270_EXPORT unsigned int lib3270_get_unlock_delay(const H3270 *hSession)
 {
 	return (unsigned int) hSession->unlock_delay_ms;
 }
diff --git a/src/core/model.c b/src/core/model.c
index 1b59ee3..3f9b6e5 100644
--- a/src/core/model.c
+++ b/src/core/model.c
@@ -84,7 +84,7 @@
  * @param hSession selected 3270 session.
  * @return Current model number.
  */
-int lib3270_get_model_number(H3270 *hSession)
+int lib3270_get_model_number(const H3270 *hSession)
 {
 	return hSession->model_num;
 }
diff --git a/src/core/properties/boolean.c b/src/core/properties/boolean.c
index 74028b0..3f6cf52 100644
--- a/src/core/properties/boolean.c
+++ b/src/core/properties/boolean.c
@@ -34,7 +34,7 @@
  #include <lib3270/properties.h>
  #include <lib3270/keyboard.h>
 
- int lib3270_is_starting(H3270 *hSession)
+ int lib3270_is_starting(const H3270 *hSession)
  {
 	return hSession->starting != 0;
  }
diff --git a/src/core/properties/signed.c b/src/core/properties/signed.c
index eb50054..8f7a22f 100644
--- a/src/core/properties/signed.c
+++ b/src/core/properties/signed.c
@@ -34,17 +34,17 @@
  #include <lib3270/properties.h>
  #include <lib3270/keyboard.h>
 
- static int lib3270_get_connection_state_as_int(H3270 *hSession)
+ static int lib3270_get_connection_state_as_int(const H3270 *hSession)
  {
 	return (int) lib3270_get_connection_state(hSession);
  }
 
- static int lib3270_get_program_message_as_int(H3270 *hSession)
+ static int lib3270_get_program_message_as_int(const H3270 *hSession)
  {
 	return (int) lib3270_get_program_message(hSession);
  }
 
- static int lib3270_get_ssl_state_as_int(H3270 * hSession)
+ static int lib3270_get_ssl_state_as_int(const H3270 * hSession)
  {
  	return (int) lib3270_get_ssl_state(hSession);
  }
diff --git a/src/core/properties/unsigned.c b/src/core/properties/unsigned.c
index 2a52a61..573fda0 100644
--- a/src/core/properties/unsigned.c
+++ b/src/core/properties/unsigned.c
@@ -34,7 +34,7 @@
  #include <lib3270/properties.h>
  #include <lib3270/keyboard.h>
 
- unsigned int lib3270_get_kybdlock_as_int(H3270 *hSession)
+ unsigned int lib3270_get_kybdlock_as_int(const H3270 *hSession)
  {
 	return (unsigned int) lib3270_get_keyboard_lock_state(hSession);
  }
diff --git a/src/core/screen.c b/src/core/screen.c
index 40f55c8..205be44 100644
--- a/src/core/screen.c
+++ b/src/core/screen.c
@@ -245,31 +245,24 @@ static unsigned short calc_attrs(H3270 *session, int baddr, int fa_addr, int fa)
 	return a;
 }
 
-LIB3270_EXPORT unsigned int lib3270_get_length(H3270 *h)
+LIB3270_EXPORT unsigned int lib3270_get_length(const H3270 *h)
 {
-	CHECK_SESSION_HANDLE(h);
 	return h->view.rows * h->view.cols;
 }
 
-LIB3270_EXPORT void lib3270_get_screen_size(H3270 *h, unsigned int *r, unsigned int *c)
+LIB3270_EXPORT void lib3270_get_screen_size(const H3270 *h, unsigned int *r, unsigned int *c)
 {
-	CHECK_SESSION_HANDLE(h);
 	*r = h->view.rows;
 	*c = h->view.cols;
-
-//	trace("%s: %d - %d",__FUNCTION__, h->rows, h->cols);
-
 }
 
-LIB3270_EXPORT unsigned int lib3270_get_width(H3270 *h)
+LIB3270_EXPORT unsigned int lib3270_get_width(const H3270 *h)
 {
-	CHECK_SESSION_HANDLE(h);
 	return h->view.cols;
 }
 
-LIB3270_EXPORT unsigned int lib3270_get_height(H3270 *h)
+LIB3270_EXPORT unsigned int lib3270_get_height(const H3270 *h)
 {
-	CHECK_SESSION_HANDLE(h);
 	return h->view.rows;
 }
 
@@ -405,7 +398,7 @@ void screen_update(H3270 *session, int bstart, int bend)
 
 }
 
-LIB3270_EXPORT unsigned int lib3270_get_cursor_address(H3270 *hSession)
+LIB3270_EXPORT unsigned int lib3270_get_cursor_address(const H3270 *hSession)
 {
 	if(check_online_session(hSession))
 		return 0;
@@ -587,9 +580,8 @@ void status_reset(H3270 *session)
  *
  * @see LIB3270_MESSAGE
  */
-LIB3270_EXPORT LIB3270_MESSAGE lib3270_get_program_message(H3270 *session)
+LIB3270_EXPORT LIB3270_MESSAGE lib3270_get_program_message(const H3270 *session)
 {
-	CHECK_SESSION_HANDLE(session);
 	return session->oia.status;
 }
 
diff --git a/src/include/lib3270.h b/src/include/lib3270.h
index 21f21fa..f99ff41 100644
--- a/src/include/lib3270.h
+++ b/src/include/lib3270.h
@@ -425,7 +425,7 @@
 	 * @param c Pointer to screen columns.
 	 *
 	 */
-	LIB3270_EXPORT void lib3270_get_screen_size(H3270 *h, unsigned int *r, unsigned int *c);
+	LIB3270_EXPORT void lib3270_get_screen_size(const H3270 *h, unsigned int *r, unsigned int *c);
 
 	/**
 	 * Get current screen width in columns.
@@ -435,7 +435,7 @@
 	 * @return screen width.
 	 *
 	 */
-	LIB3270_EXPORT unsigned int lib3270_get_width(H3270 *h);
+	LIB3270_EXPORT unsigned int lib3270_get_width(const H3270 *h);
 
 	/**
 	 * Get current screen width in rows.
@@ -445,9 +445,9 @@
 	 * @return screen rows.
 	 *
 	 */
-	LIB3270_EXPORT unsigned int lib3270_get_height(H3270 *h);
+	LIB3270_EXPORT unsigned int lib3270_get_height(const H3270 *h);
 
-	LIB3270_EXPORT unsigned int lib3270_get_length(H3270 *h);
+	LIB3270_EXPORT unsigned int lib3270_get_length(const H3270 *h);
 
 	/**
 	 * @brief Creates an empty TN3270 session.
@@ -800,7 +800,7 @@
 	 * @return Cursor address or 0 if invalid (sets errno).
 	 *
 	 */
-	LIB3270_EXPORT unsigned int lib3270_get_cursor_address(H3270 *hSession);
+	LIB3270_EXPORT unsigned int lib3270_get_cursor_address(const H3270 *hSession);
 
 	/**
 	 * @brief Move cursor
@@ -966,7 +966,7 @@
 	 * @return Latest program message.
 	 *
 	 */
-	LIB3270_EXPORT LIB3270_MESSAGE	  lib3270_get_program_message(H3270 *h);
+	LIB3270_EXPORT LIB3270_MESSAGE	  lib3270_get_program_message(const H3270 *h);
 
 	/**
 	 * Get connected LU name.
@@ -1089,7 +1089,7 @@
 
 	LIB3270_EXPORT char * lib3270_cut_selected(H3270 *hSession);
 
-	LIB3270_EXPORT int	  lib3270_has_selection(H3270 *hSession);
+	LIB3270_EXPORT int	  lib3270_has_selection(const H3270 *hSession);
 
 	/**
 	 * @brief Get all text inside the terminal.
@@ -1174,7 +1174,7 @@
      * @return -1 when failed 1 if the addr is protected and 0 if not.
      *
 	 */
-	LIB3270_EXPORT int lib3270_get_is_protected(H3270 *hSession, int baddr0);
+	LIB3270_EXPORT int lib3270_get_is_protected(const H3270 *hSession, int baddr0);
 
 	LIB3270_EXPORT int LIB3270_DEPRECATED(lib3270_is_protected(H3270 *h, unsigned int baddr));
 
@@ -1185,8 +1185,11 @@
      *
      * @return -1 when failed 1 if the session is formatted and 0 if not.
      *
+     * @retval -1	Failed (check errno for error code).
+     * @retval  0	Screen is not formatted.
+     * @retval  1	Screen is formatted.
 	 */
-	LIB3270_EXPORT int lib3270_get_is_formatted(H3270 *hSession);
+	LIB3270_EXPORT int lib3270_get_is_formatted(const H3270 *hSession);
 
 	/**
 	 * @brief Get Check if the screen position is protected.
@@ -1196,7 +1199,7 @@
 	 * @param col		Desired col.
 	 *
 	 */
-	LIB3270_EXPORT int lib3270_get_is_protected_at(H3270 *h, unsigned int row, unsigned int col);
+	LIB3270_EXPORT int lib3270_get_is_protected_at(const H3270 *h, unsigned int row, unsigned int col);
 
 	/**
 	 * @brief Get address of the first blank.
@@ -1225,7 +1228,7 @@
 	 * @exception -ENODATA		No field at the address.
 	 *
 	 */
-	LIB3270_EXPORT int lib3270_field_addr(H3270 *hSession, int baddr);
+	LIB3270_EXPORT int lib3270_field_addr(const H3270 *hSession, int baddr);
 
 	/**
 	 * @brief Get field attribute for a given buffer address.
@@ -1304,7 +1307,7 @@
 	LIB3270_EXPORT int lib3270_set_model(H3270 *hSession, const char *name);
 
 	LIB3270_EXPORT const char	* lib3270_get_model(const H3270 *session);
-	LIB3270_EXPORT int			  lib3270_get_model_number(H3270 *hSession);
+	LIB3270_EXPORT int			  lib3270_get_model_number(const H3270 *hSession);
 
 	LIB3270_EXPORT int lib3270_action(H3270 *hSession, const char *name);
 
@@ -1328,7 +1331,7 @@
 	 *
 	 */
 	LIB3270_EXPORT int lib3270_set_unlock_delay(H3270 *session, unsigned int delay);
-	LIB3270_EXPORT unsigned int lib3270_get_unlock_delay(H3270 *session);
+	LIB3270_EXPORT unsigned int lib3270_get_unlock_delay(const H3270 *session);
 
 	/**
 	 * @brief Alloc/Realloc memory buffer.
diff --git a/src/include/lib3270/keyboard.h b/src/include/lib3270/keyboard.h
index 059a9f8..fbf4a2c 100644
--- a/src/include/lib3270/keyboard.h
+++ b/src/include/lib3270/keyboard.h
@@ -69,7 +69,7 @@
 	 */
 	LIB3270_EXPORT LIB3270_KEYBOARD_LOCK_STATE lib3270_wait_for_keyboard_unlock(H3270 *hSession, int seconds);
 
-	LIB3270_EXPORT LIB3270_KEYBOARD_LOCK_STATE lib3270_get_keyboard_lock_state(H3270 *hSession);
+	LIB3270_EXPORT LIB3270_KEYBOARD_LOCK_STATE lib3270_get_keyboard_lock_state(const H3270 *hSession);
 
 	/**
 	 * @brief Set te operator error lock.
@@ -83,7 +83,7 @@
 	 *
 	 */
 	LIB3270_EXPORT int lib3270_set_lock_on_operator_error(H3270 *hSession, int enable);
-	LIB3270_EXPORT int lib3270_get_lock_on_operator_error(H3270 *hSession);
+	LIB3270_EXPORT int lib3270_get_lock_on_operator_error(const H3270 *hSession);
 
 #ifdef __cplusplus
 	}
diff --git a/src/include/lib3270/properties.h b/src/include/lib3270/properties.h
index fd5c17d..9d3a965 100644
--- a/src/include/lib3270/properties.h
+++ b/src/include/lib3270/properties.h
@@ -46,7 +46,7 @@
 	{
 		const char		* name;											///< @brief Property name.
 		const char		* description;									///< @brief Property description.
-		int (*get)(H3270 *hSession);									///< @brief Get value.
+		int (*get)(const H3270 *hSession);								///< @brief Get value.
 		int (*set)(H3270 *hSession, int value);							///< @brief Set value.
 
 	} LIB3270_INT_PROPERTY;
@@ -55,7 +55,7 @@
 	{
 		const char		* name;											///< @brief Property name.
 		const char		* description;									///< @brief Property description.
-		unsigned int (*get)(H3270 *hSession);							///< @brief Get value.
+		unsigned int (*get)(const H3270 *hSession);						///< @brief Get value.
 		int (*set)(H3270 *hSession, unsigned int value);				///< @brief Set value.
 
 	} LIB3270_UINT_PROPERTY;
diff --git a/src/selection/selection.c b/src/selection/selection.c
index 961e410..c0c2095 100644
--- a/src/selection/selection.c
+++ b/src/selection/selection.c
@@ -390,7 +390,7 @@ LIB3270_EXPORT char * lib3270_get_field_string_at(H3270 *session, int baddr)
 	return lib3270_get_string_at_address(session,first,lib3270_field_length(session,first)+1,0);
 }
 
-LIB3270_EXPORT int lib3270_has_selection(H3270 *hSession)
+LIB3270_EXPORT int lib3270_has_selection(const H3270 *hSession)
 {
 	if(check_online_session(hSession))
 		return 0;
--
libgit2 0.21.2