PERROR(3C-SysV)     RISC/os Reference Manual      PERROR(3C-SysV)



NAME
     perror, errno, sys_errlist, sys_nerr - system error messages

SYNOPSIS
     #include <bsd/sys/types.h>

     void perror (s)
     char *s;

     extern int errno;

     extern char *syserrlist[ ];

     extern int sysnerr;

     extern char *syserrnolist[ ];

     extern int sysnerrno;

DESCRIPTION
     perror produces a message on the standard error output,
     describing the last error encountered during a call to a
     system or library function.

     By default, the message printed consists of the text given
     by the argument to perror, followed by a colon and a space
     if the text is non-empty, followed by the system message
     corresponding to the error number.  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.  All error messages end with a newline.

     The environment variable PERROR_FMT can be set to a non-
     empty string containing the format of the error message.
     Text from the string is copied as-is except for a set of %-
     specifiers described below:

     %p    The standard message as described above.

     %t    The argument to perror.

     %c    A colon (:) if the argument to perror is nonempty;
           otherwise an empty string.

     %s    A colon (:) followed by a space if the argument to
           perror is nonempty; otherwise an empty string.

     %m    The system message that corresponds to the error
           number.

     %e    The symbolic name for the error number.




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PERROR(3C-SysV)     RISC/os Reference Manual      PERROR(3C-SysV)



     %n    The error number.

     %%    The character %.

     A % followed by any other character causes the % and the
     character to be printed.

     As an example, assume that perror is called after a failed
     call to open(2) that sets the error number to 2, and that
     the argument to perror is ``myfile''.  If PERROR_FMT is ``%t
     %s%m - (%e)'', the resulting message will be

          myfile : No such file or directory - (ENOENT)

     To simplify variant formatting of messages, the array of
     message strings syserrlist and the array is provided; errno
     can be used as an index into these tables to get the strings
     without the new-line.  sysnerr and sysnerrno are the
     number of messages in the tables; they should be checked
     because new error codes may be added to the system before
     they are added to the tables.  Note that in future releases
     of this system, a routine will be provided to return the
     formatted message without the newline, so that programs that
     need to format messages can do so.

SEE ALSO
     intro(2).

ERRORS
     Many programs do not use perror so the formatting is not
     always useful.  These programs should be fixed.
























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