explain_unsetenv - explain
unsetenv(3) errors
#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);
These functions may be used to obtain explanations for errors returned by the
unsetenv(3) system call.
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.
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.
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.
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.
- unsetenv(3)
- change or add an environment variable
- explain_unsetenv_or_die(3)
- change or add an environment variable and report errors
libexplain version 1.3
Copyright (C) 2010 Peter Miller