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explain_unsetenv(3)	   Library Functions Manual	   explain_unsetenv(3)

NAME
       explain_unsetenv	- explain unsetenv(3) errors

SYNOPSIS
       #include	<libexplain/unsetenv.h>
       const char *explain_unsetenv(const char *name);
       const char *explain_errno_unsetenv(int errnum, const char *name);
       void explain_message_unsetenv(char *message, int	message_size, const
       char *name);
       void explain_message_errno_unsetenv(char	*message, int message_size,
       int errnum, const char *name);

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

   explain_unsetenv
       const char *explain_unsetenv(const char *name);

       The explain_unsetenv function is	used to	obtain an  explanation	of  an
       error  returned	by  the	unsetenv(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.

       name    The original name, exactly as passed to the unsetenv(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 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:
	      if (unsetenv(name) < 0)
	      {
		  fprintf(stderr, "%s\n", explain_unsetenv(name));
		  exit(EXIT_FAILURE);
	      }

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

   explain_errno_unsetenv
       const char *explain_errno_unsetenv(int errnum, const char *name);

       The explain_errno_unsetenv function is used to obtain an	explanation of
       an  error  returned by the unsetenv(3) system call.  The	least the mes-
       sage 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.

       name    The  original name, exactly as passed to	the unsetenv(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 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:
	      if (unsetenv(name) < 0)
	      {
		  int err = errno;
		  fprintf(stderr, "%s\n", explain_errno_unsetenv(err, name));
		  exit(EXIT_FAILURE);
	      }

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

   explain_message_unsetenv
       void explain_message_unsetenv(char *message, int	message_size, const
       char *name);

       The explain_message_unsetenv function is	used to	obtain an  explanation
       of  an  error  returned	by the unsetenv(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.

       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.

       name    The  original name, exactly as passed to	the unsetenv(3)	system
	       call.

       Example:	This function is intended to be	used in	a fashion  similar  to
       the following example:
	      if (unsetenv(name) < 0)
	      {
		  char message[3000];
		  explain_message_unsetenv(message, sizeof(message), name);
		  fprintf(stderr, "%s\n", message);
		  exit(EXIT_FAILURE);
	      }

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

   explain_message_errno_unsetenv
       void explain_message_errno_unsetenv(char	*message, int message_size,
       int errnum, const char *name);

       The explain_message_errno_unsetenv function is used to obtain an	expla-
       nation of an error returned by the unsetenv(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  de-
       tail.

       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.

       name    The original name, exactly as passed to the unsetenv(3)	system
	       call.

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

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

SEE ALSO
       unsetenv(3)
	       change or add an	environment variable

       explain_unsetenv_or_die(3)
	       change or add an	environment variable and report	errors

COPYRIGHT
       libexplain version 1.3
       Copyright (C) 2010 Peter	Miller

							   explain_unsetenv(3)

NAME | SYNOPSIS | DESCRIPTION | SEE ALSO | COPYRIGHT

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