PERROR(III)                  11/5/73                  PERROR(III)


     perror, sys_errlist, sys_nerr, errno - system error messages



     char *s;

     int sys_nerr;

     char *sys_errlist[];

     int errno;


     Perror produces a short error message  describing  the  last

     error  encountered  during  a  call  to  the system from a C

     program.  First the argument string s  is  printed,  then  a

     colon,  then the message and a new-line.  Most usefully, the

     argument string is the name of the  program  which  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.

     To simplify variant formatting of messages,  the  vector  of

     message  strings  sys_errlist is provided; errno can be used

     as an index in this table to get the message string  without

     the   newline.   Sys_nerr  is  the  largest  message  number

     provided for in the table; it should be checked because  new

     error codes may be added to the system before they are added

     to the table.


     Introduction to System Calls