explain_select(3)					     Library Functions Manual						 explain_select(3)

NAME

       explain_select - explain select(2) errors

SYNOPSIS

       #include <sys/select.h> #include <libexplain/select.h>
       const char *explain_select(int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout);
       const char *explain_errno_select(int errnum, int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout);
       void explain_message_select(char *message, int message_size, int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval
       *timeout);
       void explain_message_errno_select(char *message, int message_size,  int	errnum,  int  nfds,  fd_set  *readfds,	fd_set	*writefds,  fd_set
       *exceptfds, struct timeval *timeout);

DESCRIPTION

       These functions may be used to obtain explanations for errors returned by the select(2) system call.

   explain_select
       const char *explain_select(int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout);

       The explain_select function is used to obtain an explanation of an error returned by the select(2) system call.	The least the message will
       contain is the value of strerror(errno), but usually it will do much better, and indicate the underlying cause in more detail.

       The errno global variable will be used to obtain the error value to be decoded.

       This function is intended to be used in a fashion similar to the following example:
	      if (select(nfds, readfds, writefds, exceptfds, timeout) < 0)
	      {
		  fprintf(stderr, "%s
", explain_select(nfds,
		      readfds, writefds, exceptfds, timeout));
		  exit(EXIT_FAILURE);
	      }

       nfds    The original nfds, exactly as passed to the select(2) system call.

       readfds The original readfds, exactly as passed to the select(2) system call.

       writefds
	       The original writefds, exactly as passed to the select(2) system call.

       exceptfds
	       The original exceptfds, exactly as passed to the select(2) system call.

       timeout The original timeout, exactly as passed to the select(2) system call.

       Returns:
	       The message explaining the error.  This message buffer is shared by all libexplain functions which do not supply a buffer in  their
	       argument  list.	 This  will  be  overwritten by the next call to any libexplain function which shares this buffer, including other
	       threads.

       Note: This function is not thread safe, because it shares a return buffer across all threads, and many other functions in this library.

   explain_errno_select
       const char *explain_errno_select(int errnum, int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout);

       The explain_errno_select function is used to obtain an explanation of an error returned by the select(2) system call.  The least  the  mes-
       sage will contain is the value of strerror(errnum), but usually it will do much better, and indicate the underlying cause in more detail.

       This function is intended to be used in a fashion similar to the following example:
	      if (select(nfds, readfds, writefds, exceptfds, timeout) < 0)
	      {
		  int err = errno;
		  fprintf(stderr, "%s
", explain_errno_select(err,
		      nfds, readfds, writefds, exceptfds, timeout));
		  exit(EXIT_FAILURE);
	      }

       errnum  The error value to be decoded, usually obtained from the errno global variable just before this function is called.  This is neces-
	       sary if you need to call any code between the system call to be explained and this function, because many libc functions will alter
	       the value of errno.

       nfds    The original nfds, exactly as passed to the select(2) system call.

       readfds The original readfds, exactly as passed to the select(2) system call.

       writefds
	       The original writefds, exactly as passed to the select(2) system call.

       exceptfds
	       The original exceptfds, exactly as passed to the select(2) system call.

       timeout The original timeout, exactly as passed to the select(2) system call.

       Returns:
	       The  message explaining the error.  This message buffer is shared by all libexplain functions which do not supply a buffer in their
	       argument list.  This will be overwritten by the next call to any libexplain function which  shares  this  buffer,  including  other
	       threads.

       Note: This function is not thread safe, because it shares a return buffer across all threads, and many other functions in this library.

   explain_message_select
       void explain_message_select(char *message, int message_size, int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval
       *timeout);

       The explain_message_select function may be used to  obtain an explanation of an error returned by the select(2) system call.  The least the
       message will contain is the value of strerror(errno), but usually it will do much better, and indicate the underlying cause in more detail.

       The errno global variable will be used to obtain the error value to be decoded.

       This function is intended to be used in a fashion similar to the following example:
	      if (select(nfds, readfds, writefds, exceptfds, timeout) < 0)
	      {
		  char message[3000];
		  explain_message_select(message, sizeof(message),
		      nfds, readfds, writefds, exceptfds, timeout);
		  fprintf(stderr, "%s
", message);
		  exit(EXIT_FAILURE);
	      }

       message The  location  in  which  to  store the returned message.  If a suitable message return buffer is supplied, this function is thread
	       safe.

       message_size
	       The size in bytes of the location in which to store the returned message.

       nfds    The original nfds, exactly as passed to the select(2) system call.

       readfds The original readfds, exactly as passed to the select(2) system call.

       writefds
	       The original writefds, exactly as passed to the select(2) system call.

       exceptfds
	       The original exceptfds, exactly as passed to the select(2) system call.

       timeout The original timeout, exactly as passed to the select(2) system call.

   explain_message_errno_select
       void explain_message_errno_select(char *message, int message_size,  int	errnum,  int  nfds,  fd_set  *readfds,	fd_set	*writefds,  fd_set
       *exceptfds, struct timeval *timeout);

       The  explain_message_errno_select  function  may  be  used to obtain an explanation of an error returned by the select(2) system call.  The
       least the message will contain is the value of strerror(errnum), but usually it will do much better, and indicate the underlying  cause	in
       more detail.

       This function is intended to be used in a fashion similar to the following example:
	      if (select(nfds, readfds, writefds, exceptfds, timeout) < 0)
	      {
		  int err = errno;
		  char message[3000];
		  explain_message_errno_select(message, sizeof(message), err,
		      nfds, readfds, writefds, exceptfds, timeout);
		  fprintf(stderr, "%s
", message);
		  exit(EXIT_FAILURE);
	      }

       message The  location  in  which  to  store the returned message.  If a suitable message return buffer is supplied, this function is thread
	       safe.

       message_size
	       The size in bytes of the location in which to store the returned message.

       errnum  The error value to be decoded, usually obtained from the errno global variable just before this function is called.  This is neces-
	       sary if you need to call any code between the system call to be explained and this function, because many libc functions will alter
	       the value of errno.

       nfds    The original nfds, exactly as passed to the select(2) system call.

       readfds The original readfds, exactly as passed to the select(2) system call.

       writefds
	       The original writefds, exactly as passed to the select(2) system call.

       exceptfds
	       The original exceptfds, exactly as passed to the select(2) system call.

       timeout The original timeout, exactly as passed to the select(2) system call.

SEE ALSO

       select(2)
	       blah blah

       explain_select_or_die(3)
	       blah blah and report errors

COPYRIGHT

       libexplain version 0.52
       Copyright (C) 2008 Peter Miller

																 explain_select(3)