man NJB_Discover (Fonctions bibliothèques) - Locate NJB devices on available USB busses
NAME
NJB_Discover - Locate NJB devices on available USB busses
LIBRARY
libnjb
SYNOPSIS
#include <libnjb.h>
extern int njb_error;
int NJB_Discover (njb_t *njbs, int limit, int *n)
DESCRIPTION
This function searches all configured USB busses for attached NJB devices.
The number of NJB devices found is placed into n, and the njb_t array *njbs is populated with n elements, describing the NJB's in the order in which they are found. It is the user's responsibility to ensure that the *njbs array is of sufficient size. A good practice is to declare an array with NJB_MAX_DEVICES elements: while this is slightly wasteful in terms of memory, it will always guarantee that sufficient storage is available.
The limit parameter can be used to restrict the search to limit busses (starting with /dev/usb0, and counting up). If set to 0, then no limit is enforced, and all busses will be queried.
RETURN VALUES
NJB_Discover returns 0 if no errors occurred. If any errors were encountered during the search, then -1 is returned. njb_error will not be set to a meaningful value, but the njb_error(3) functions can still be used to obtain error messages corresponding to the problems found.
It is extremely important to note that an error does not automatically imply a failure. You should always check the value stored in n to determine how many NJB devices were discovered, if any, regardless of the return value of NJB_Discover. Because multiple USB controllers can be present on a system, it is entirely possible, for example, that /dev/usb1 could not be opened while an NJB device on /dev/usb0 was located successfully. In this case, NJB_Discover would still return -1, but n would be set to 1, and the njbs array would have a valid NJB device in described in njbs[0].
Conversely, NJB_Discover can return 0 even if no NJB devices are found. In this case, there were no errors opening the available USB busses, but no NJB devices were attached and/or ready for communication.
SEE ALSO
BUGS
The author is aware that the term "USB busses" is redundant (like "ATM machine"). It would be more correct to say "USBs", but that doesn't flow as well.