perror
produces a message on the standard error output (file descriptor 2),
describing the last error encountered
during a call to a system or library function.
The argument string
s
is printed first, then a colon and a blank, then the message and a newline.
(However, if s
is a null pointer or points to a null string,
the colon is not printed.)
To be of most use, the argument string should include the name
of the program that incurred the error.
The error number is taken from the external variable
errno, which is set when errors occur but not cleared when
non-erroneous calls are made.
s);