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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;
       int errno;

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.   First  (if  s  is  not NULL and *s is not NUL) the
       argument string s is printed, followed by 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

       The function perror() and the external errno (see errno(3)) conform  to
       ANSI  C, 4.3BSD, POSIX, X/OPEN.  The externals sys_nerr and sys_errlist
       conform to BSD.

NOTE

       The externals sys_nerr and sys_errlist are defined  by  glibc,  but  in
       <stdio.h>.

SEE ALSO

       errno(3), strerror(3)

                                  2001-12-14                         PERROR(3)