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NAME

       explain_popen - explain popen(3) errors

SYNOPSIS

       #include <libexplain/popen.h>
       const char *explain_popen(const char *command, const char *flags);
       const  char *explain_errno_popen(int errnum, const char *command, const
       char *flags);
       void explain_message_popen(char *message, int message_size, const  char
       *command, const char *flags);
       void  explain_message_errno_popen(char  *message, int message_size, int
       errnum, const char *command, const char *flags);

DESCRIPTION

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

   explain_popen
       const char *explain_popen(const char *command, const char *flags);

       The explain_popen function is used to obtain an explanation of an error
       returned by the popen(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:
              FILE *fp = popen(command, flags);
              if (!fp)
              {
                  fprintf(stderr, "%s\n", explain_popen(command, flags));
                  exit(EXIT_FAILURE);
              }

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

       command The  original command, exactly as passed to the popen(3) system
               call.

       flags   The original flags, exactly as passed to  the  popen(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_popen
       const char *explain_errno_popen(int errnum, const char *command,  const
       char *flags);

       The explain_errno_popen function is used to obtain an explanation of an
       error returned by the popen(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:
              FILE *fp = popen(command, flags);
              if (!fp)
              {
                  int err = errno;
                  fprintf(stderr, "%s\n", explain_errno_popen(err, command, flags));
                  exit(EXIT_FAILURE);
              }

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

       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.

       command The original command, exactly as passed to the popen(3)  system
               call.

       flags   The  original  flags,  exactly as passed to the popen(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_popen
       void  explain_message_popen(char *message, int message_size, const char
       *command, const char *flags);

       The  explain_message_popen  function  may  be  used   to    obtain   an
       explanation  of  an  error  returned  by the popen(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:
              FILE *fp = popen(command, flags);
              if (!fp)
              {
                  char message[3000];
                  explain_message_popen(message, sizeof(message), command, flags);
                  fprintf(stderr, "%s\n", message);
                  exit(EXIT_FAILURE);
              }

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

       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.

       command The original command, exactly as passed to the popen(3)  system
               call.

       flags   The  original  flags,  exactly as passed to the popen(3) system
               call.

   explain_message_errno_popen
       void explain_message_errno_popen(char *message, int  message_size,  int
       errnum, const char *command, const char *flags);

       The  explain_message_errno_popen  function  may  be  used  to obtain an
       explanation of an error returned by  the  popen(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:
              FILE *fp = popen(command, flags);
              if (!fp)
              {
                  int err = errno;
                  char message[3000];
                  explain_message_errno_popen(message, sizeof(message),
                      err, command, flags);
                  fprintf(stderr, "%s\n", message);
                  exit(EXIT_FAILURE);
              }

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

       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.

       command The original command, exactly as passed to the popen(3)  system
               call.

       flags   The  original  flags,  exactly as passed to the popen(3) system
               call.

SEE ALSO

       popen(3)
               process I/O

       explain_popen_or_die(3)
               process I/O and report errors

COPYRIGHT

       libexplain version 0.19
       Copyright (C) 2009 Peter Miller

                                                              explain_popen(3)