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NAME

       perror - print a system error message

SYNOPSIS

       #include <stdio.h>

       void perror(const char *s);

       #include <errno.h>

       const char *sys_errlist[];
       int sys_nerr;

DESCRIPTION

       The  routine  perror() produces a message on the standard error output,
       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 new-line.  To be of most  use,  the
       argument  string  should include the name of the function 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.

       The global error list sys_errlist[] indexed by errno  can  be  used  to
       obtain  the  error  message  without  the newline.  The largest message
       number provided in the table is sys_nerr -1.  Be careful when  directly
       accessing this list because new error values may not have been added to
       sys_errlist[].

       When a system call fails, it usually returns -1 and sets  the  variable
       errno to a value describing what went wrong. (These values can be found
       in <errno.h>.)  Many  library  functions  do  likewise.   The  function
       perror()  serves to translate this error code into human-readable form.
       Note that errno is undefined after a successful library call: this call
       may  well  change  this  variable, even though it succeeds, for example
       because it internally used some other  library  function  that  failed.
       Thus,  if  a  failing  call  is  not  immediately followed by a call to
       perror, the value of errno should be saved.

CONFORMING TO

       ANSI C, BSD 4.3, POSIX, X/OPEN

SEE ALSO

       strerror(3)

                                  May 16 1996                        PERROR(3)