Provided by: libexplain-dev_1.4.D001-2_amd64 
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)