comedi_errno

Description

When a Comedilib function fails, it usually returns -1 or NULL, depending on the return type. An internal library variable stores an error number, which can be retrieved with comedi_errno(). This error number can be converted to a human-readable form by the functions comedi_perror() and comedi_strerror().

These functions are intended to mimic the behavior of the standard C library functions perror(), strerror(), and errno. In particular, Comedilib functions sometimes return an error that is generated inside the C library; the comedi error message in this case is the same as the C library.

The function comedi_errno() returns an integer describing the most recent comedilib error. This integer may be used as the errnum parameter for comedi_strerror().

Note that comedi_errno() is deliberately different than the variable errno. This is to overcome difficulties in making errno thread-safe.