Most library functions return the integer 0 on success and the integer -1 on failure. The most recent error status is reflected in the global variable cnet_errno. All values of cnet_errno will be instances of the enumerated type CnetError. Errors may be reported to stderr with cnet_perror() and their error message string accessed by indexing *cnet_errstr[] with (int)cnet_errno.
CNET_write_application, CNET_read_application, CNET_enable_application, CNET_disable_application and CNET_set_handler(EV_APPLICATIONLAYER,...) or CNET_set_handler(EV_KEYBOARDREADY,...)
are only valid if called from a node of node type NT_HOST. Function calls to either the Application or Physical Layers are invalid when cnet is not running (this can occur under X-windows when the simulation is paused and a node's debug button is selected).