Chapter 9. Handling Errors

The ToolTalk service returns error status in the function's return value rather than in a global variable. ToolTalk functions return one of these error values:

Each return type is handled differently to determine if an error occurred. For example, the return value for tt_default_session_set() is a Tt_status code. If the ToolTalk service sets the default session to the specified sessid:

Retrieving ToolTalk Error Status

You can use the ToolTalk error handling functions shown in Table 9-1 to retrieve error values.

Table 9-1. Retrieving ToolTalk Error Status

Return Type

Tool Talk Functions

char *

tt_status_message(Tt_status ttrc)


tt_int_error(int return_val)

Checking ToolTalk Error Status

You can use the ToolTalk error macros shown in Table 9-2 to check error values

Table 9-2. ToolTalk Error Macros

Return Type

ToolTalk Macros





Returned Value Status

Functions with Natural Return Values

If a ToolTalk function has a natural return value such as a pointer or an integer, a special error value is returned instead of the real value.

Functions with No Natural Return Values

If a ToolTalk function does not have a natural return value, the return value is an element of Tt_status enum. To see if there is an error, use the ToolTalk macro tt_is_err(), which returns an integer.

  • If the return value is 0, the Tt_status enum is either TT_OK or a warning.

  • If the return value is 1, the Tt_status enum is an error.

If there is an error, you can use the tt_status_message() function to obtain the character string that explains the Tt_status code, as shown in the following code example.

   char *spec_id, my_application_name;
   Tt_status tterr;
   tterr = tt_spec_write(spec_id);
   if (tt_is_err(tterr)) {
      fprintf(stderr, “%s: %s\n”, my_application_name,

Returned Pointer Status

If an error occurs during a ToolTalk function that returns a pointer, the ToolTalk service provides an address within the ToolTalk API library that contains the appropriate Tt_status code. To check whether the pointer is valid, you can use the ToolTalk macro tt_ptr_error(). If the pointer is an error value, you can use tt_status_message() to get the Tt_status character string.

The following sample code checks the pointer and retrieves and prints the Tt_status character string if an error value is found.

char *old_spec_id, new_file, new_spec_id, my_application_name;
Tt_status tterr;

new_spec_id = tt_spec_move(old_spec_id, new_file);
tterr = tt_ptr_error(new_spec_id);
switch (tterr) {
    case TT_OK:
    * Replace old_spec_id with new_spec_id in my internal
    * data structures.
   update_my_spec_ids(old_spec_id, new_spec_id);
    * The spec must have stayed in the same filesystem,
    * since ToolTalk is reusing the spec id. Do nothing.
    case TT_ERR_FILE:
    case TT_ERR_ACCESS:
   fprintf(stderr, “%s: %s\n”, my_application_name,

Returned Integer Status

If an error occurs during a ToolTalk function that returns an integer, the return value is out-of-bounds values. The tt_int_error() function returns a status of TT_OK if the value is not very out-of-bounds.

If a value is very out-of-bounds, you can use the tt_is_err() macro to determine if an error or a warning occurred.

To retrieve the character string for a Tt_status code, you can use tt_status_message().

The following sample code checks a returned integer.

Tt_message msg;
int num_args;
Tt_status tterr;
char *my_application_name;

num_args = tt_message_args_count(msg);
tterr = tt_int_error(num_args);
if (tt_is_err(tterr)) {
   fprintf(stderr, “%s: %s\n”, my_application_name,

Error Propagation

ToolTalk functions that accept pointers always check the pointer passed in and return TT_ERR_POINTER if the pointer is an error value. This check allows you to combine calls in reasonable ways without checking the value of the pointer for every single call.

In the following code sample, a message is created, filled in, and sent. If tt_message_create() fails, an error object is assigned to m, and all the tt_message_xxx_set() and tt_message_send() calls fail. To detect the error without checking between each call, you only need to check the return code from tt_message_send().

Tt_message m;
if (tt_rc!=TT_OK)..