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NAME

       explain_ferror - explain ferror(3) errors

SYNOPSIS

       #include <libexplain/ferror.h>
       const char *explain_ferror(FILE *fp);
       const char *explain_errno_ferror(int errnum, FILE *fp);
       void explain_message_ferror(char *message, int message_size, FILE *fp);
       void explain_message_errno_ferror(char *message, int message_size,  int
       errnum, FILE *fp);

DESCRIPTION

       These  functions may be used to obtain explanations for errors returned
       by the ferror(3) system call.

   explain_ferror
       const char *explain_ferror(FILE *fp);

       The explain_ferror function is used to  obtain  an  explanation  of  an
       error  returned  by  the  ferror(3) 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 (ferror(fp) < 0)
              {
                  fprintf(stderr, "%s\n", explain_ferror(fp));
                  exit(EXIT_FAILURE);
              }

       It  is  essential that this function cal be placed as close as possible
       to the I/O code that has caused the problem, otherwise intervening code
       could have altered the errno global variable.

       fp      The  original  fp,  exactly  as  passed to the ferror(3) 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_ferror
       const char *explain_errno_ferror(int errnum, FILE *fp);

       The  explain_errno_ferror  function is used to obtain an explanation of
       an error returned by the ferror(3) 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 (ferror(fp) < 0)
              {
                  int err = errno;
                  fprintf(stderr, "%s\n", explain_errno_ferror(err, fp));
                  exit(EXIT_FAILURE);
              }

       It  is  essential that this function cal be placed as close as possible
       to the I/O code that has caused the problem, otherwise intervening code
       could have altered the errno global variable.

       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.

       fp      The  original  fp,  exactly  as  passed to the ferror(3) 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_ferror
       void explain_message_ferror(char *message, int message_size, FILE *fp);

       The  explain_message_ferror  function  may  be  used  to    obtain   an
       explanation  of  an  error  returned by the ferror(3) 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 (ferror(fp) < 0)
              {
                  char message[3000];
                  explain_message_ferror(message, sizeof(message), fp);
                  fprintf(stderr, "%s\n", message);
                  exit(EXIT_FAILURE);
              }

       It is essential that this function cal be placed as close  as  possible
       to the I/O code that has caused the problem, otherwise intervening code
       could have altered the errno global variable.

       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.

       fp      The  original  fp,  exactly  as  passed to the ferror(3) system
               call.

   explain_message_errno_ferror
       void explain_message_errno_ferror(char *message, int message_size,  int
       errnum, FILE *fp);

       The  explain_message_errno_ferror  function  may  be  used to obtain an
       explanation of an error returned by the  ferror(3)  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 (ferror(fp) < 0)
              {
                  int err = errno;
                  char message[3000];
                  explain_message_errno_ferror(message, sizeof(message), err, fp);
                  fprintf(stderr, "%s\n", message);
                  exit(EXIT_FAILURE);
              }

       It is essential that this function cal be placed as close  as  possible
       to the I/O code that has caused the problem, otherwise intervening code
       could have altered the errno global variable.

       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
               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.

       fp      The  original  fp,  exactly  as  passed to the ferror(3) system
               call.

SEE ALSO

       ferror(3)
               check stream status

       explain_ferror_or_die(3)
               check stream status and report errors

COPYRIGHT

       libexplain version 0.19
       Copyright (C) 2008 Peter Miller

                                                             explain_ferror(3)