The <errno.h> header file defines several macros used
for error reporting.
EDOM
ERANGE
errno . They
expand to integral constant expressions with unique nonzero
values.
errno
int , depending on the operating
system.
The errno variable is used for holding
implementation-defined error codes from library routines.
All error codes are positive integers. The value of
errno is 0 at program startup, but is never set to
0 by any library function. Therefore, errno should
be set to 0 before calling a library function and then inspected
afterward.