Provided by: libexplain-dev_1.4.D001-12_amd64 bug

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 buffer 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_unsetenv_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 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.

       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 buffer 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_unsetenv_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 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.

       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_unsetenv_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 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.

       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.

       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_unsetenv_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 1.4
       Copyright (C) 2010 Peter Miller

                                                                              explain_unsetenv(3)