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explain_pread(3)	   Library Functions Manual	      explain_pread(3)

NAME
       explain_pread - explain pread(2)	errors

SYNOPSIS
       #include	<libexplain/pread.h>
       const char *explain_pread(int fildes, void *data, size_t	data_size,
       off_t offset);
       const char *explain_errno_pread(int errnum, int fildes, void *data,
       size_t data_size, off_t offset);
       void explain_message_pread(char *message, int message_size, int fildes,
       void *data, size_t data_size, off_t offset);
       void explain_message_errno_pread(char *message, int message_size, int
       errnum, int fildes, void	*data, size_t data_size, off_t offset);

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

   explain_pread
       const char *explain_pread(int fildes, void *data, size_t	data_size,
       off_t offset);

       The explain_pread function is used to obtain an explanation of an error
       returned	by the pread(2)	system call. The least the message  will  con-
       tain  is	the value of strerror(errno), but usually it will do much bet-
       ter, and	indicate the underlying	cause in more detail.

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

       fildes  The  original  fildes, exactly as passed	to the pread(2)	system
	       call.

       data    The original data, exactly as passed  to	 the  pread(2)	system
	       call.

       data_size
	       The  original data_size,	exactly	as passed to the pread(2) sys-
	       tem call.

       offset  The original offset, exactly as passed to the  pread(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 buf-
       fer across all threads, and many	other functions	in this	library.

       Example:	This function is intended to be	used in	a fashion  similar  to
       the following example:
	      ssize_t result = pread(fildes, data, data_size, offset);
	      if (result < 0)
	      {
		  fprintf(stderr, "%s\n", explain_pread(fildes,	data,
		  data_size, offset));
		  exit(EXIT_FAILURE);
	      }

       The  above  code	 example  is  available	 pre-packaged	as   the   ex-
       plain_pread_or_die(3) function.

   explain_errno_pread
       const char *explain_errno_pread(int errnum, int fildes, void *data,
       size_t data_size, off_t offset);

       The explain_errno_pread function	is used	to obtain an explanation of an
       error  returned by the pread(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.

       errnum  The  error value	to be decoded, usually obtained	from the errno
	       global variable just before this	function is  called.  This  is
	       necessary  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.

       fildes  The  original  fildes, exactly as passed	to the pread(2)	system
	       call.

       data    The original data, exactly as passed  to	 the  pread(2)	system
	       call.

       data_size
	       The  original data_size,	exactly	as passed to the pread(2) sys-
	       tem call.

       offset  The original offset, exactly as passed to the  pread(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 buf-
       fer across all threads, and many	other functions	in this	library.

       Example:	This function is intended to be	used in	a fashion  similar  to
       the following example:
	      ssize_t result = pread(fildes, data, data_size, offset);
	      if (result < 0)
	      {
		  int err = errno;
		  fprintf(stderr, "%s\n", explain_errno_pread(err, fildes,
		  data,	data_size, offset));
		  exit(EXIT_FAILURE);
	      }

       The  above  code	 example  is  available	 pre-packaged	as   the   ex-
       plain_pread_or_die(3) function.

   explain_message_pread
       void explain_message_pread(char *message, int message_size, int fildes,
       void *data, size_t data_size, off_t offset);

       The explain_message_pread function is used to obtain an explanation  of
       an  error  returned  by the pread(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.

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

       message_size
	       The size	in bytes of the	location in which  to  store  the  re-
	       turned message.

       fildes  The  original  fildes, exactly as passed	to the pread(2)	system
	       call.

       data    The original data, exactly as passed  to	 the  pread(2)	system
	       call.

       data_size
	       The  original data_size,	exactly	as passed to the pread(2) sys-
	       tem call.

       offset  The original offset, exactly as passed to the  pread(2)	system
	       call.

       Example:	 This  function	is intended to be used in a fashion similar to
       the following example:
	      ssize_t result = pread(fildes, data, data_size, offset);
	      if (result < 0)
	      {
		  char message[3000];
		  explain_message_pread(message, sizeof(message), fildes,
		  data,	data_size, offset);
		  fprintf(stderr, "%s\n", message);
		  exit(EXIT_FAILURE);
	      }

       The   above   code   example  is	 available  pre-packaged  as  the  ex-
       plain_pread_or_die(3) function.

   explain_message_errno_pread
       void explain_message_errno_pread(char *message, int message_size, int
       errnum, int fildes, void	*data, size_t data_size, off_t offset);

       The  explain_message_errno_pread	function is used to obtain an explana-
       tion of an error	returned by the	pread(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.

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

       message_size
	       The size	in bytes of the	location in which  to  store  the  re-
	       turned message.

       errnum  The  error value	to be decoded, usually obtained	from the errno
	       global variable just before this	function is  called.  This  is
	       necessary  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.

       fildes  The  original  fildes, exactly as passed	to the pread(2)	system
	       call.

       data    The original data, exactly as passed  to	 the  pread(2)	system
	       call.

       data_size
	       The  original data_size,	exactly	as passed to the pread(2) sys-
	       tem call.

       offset  The original offset, exactly as passed to the  pread(2)	system
	       call.

       Example:	 This  function	is intended to be used in a fashion similar to
       the following example:
	      ssize_t result = pread(fildes, data, data_size, offset);
	      if (result < 0)
	      {
		  int err = errno;
		  char message[3000];
		  explain_message_errno_pread(message, sizeof(message),	err,
		  fildes, data,	data_size, offset);
		  fprintf(stderr, "%s\n", message);
		  exit(EXIT_FAILURE);
	      }

       The   above   code   example  is	 available  pre-packaged  as  the  ex-
       plain_pread_or_die(3) function.

SEE ALSO
       pread(2)
	       read from or write to a file descriptor at a given offset

       explain_pread_or_die(3)
	       read from or write to a file descriptor at a given  offset  and
	       report errors

COPYRIGHT
       libexplain version 1.3
       Copyright (C) 2009 Peter	Miller

							      explain_pread(3)

NAME | SYNOPSIS | DESCRIPTION | SEE ALSO | COPYRIGHT

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