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Manual Reference Pages  -  EXPLAIN_SELECT (3)

NAME

explain_select - explain select(2) errors

CONTENTS

Synopsis
Description
See Also
Copyright

SYNOPSIS

#include <sys/select.h> #include <libexplain/select.h>

const char *explain_select(int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout);
const char *explain_errno_select(int errnum, int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout);
void explain_message_select(char *message, int message_size, int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout);
void explain_message_errno_select(char *message, int message_size, int errnum, int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout);

DESCRIPTION

These functions may be used to obtain explanations for errors returned by the I]select(2) system call.

    explain_select

const char *explain_select(int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout);

The B]explain_select function is used to obtain an explanation of an error returned by the I]select(2) system call. The least the message will contain is the value of CW]strerror(errno), but usually it will do much better, and indicate the underlying cause in more detail.

The I]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:

if (select(nfds, readfds, writefds, exceptfds, timeout) < 0)
{
    fprintf(stderr, "%s\n", explain_select(nfds,
        readfds, writefds, exceptfds, timeout));
    exit(EXIT_FAILURE);
}

I]nfds The original nfds, exactly as passed to the I]select(2) system call.
I]readfds
  The original readfds, exactly as passed to the I]select(2) system call.
I]writefds
  The original writefds, exactly as passed to the I]select(2) system call.
I]exceptfds
  The original exceptfds, exactly as passed to the I]select(2) system call.
I]timeout
  The original timeout, exactly as passed to the I]select(2) 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.
B]Note: This function is B]not thread safe, because it shares a return buffer across all threads, and many other functions in this library.

    explain_errno_select

const char *explain_errno_select(int errnum, int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout);

The B]explain_errno_select function is used to obtain an explanation of an error returned by the I]select(2) system call. The least the message will contain is the value of CW]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:

if (select(nfds, readfds, writefds, exceptfds, timeout) < 0)
{
    int err = errno;
    fprintf(stderr, "%s\n", explain_errno_select(err,
        nfds, readfds, writefds, exceptfds, timeout));
    exit(EXIT_FAILURE);
}

I]errnum The error value to be decoded, usually obtained from the I]errno global variable just before this function is called. This is necessary if you need to call B]any code between the system call to be explained and this function, because many libc functions will alter the value of I]errno.
I]nfds The original nfds, exactly as passed to the I]select(2) system call.
I]readfds
  The original readfds, exactly as passed to the I]select(2) system call.
I]writefds
  The original writefds, exactly as passed to the I]select(2) system call.
I]exceptfds
  The original exceptfds, exactly as passed to the I]select(2) system call.
I]timeout
  The original timeout, exactly as passed to the I]select(2) 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.
B]Note: This function is B]not thread safe, because it shares a return buffer across all threads, and many other functions in this library.

    explain_message_select

void explain_message_select(char *message, int message_size, int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout);

The B]explain_message_select function may be used to obtain an explanation of an error returned by the I]select(2) system call. The least the message will contain is the value of CW]strerror(errno), but usually it will do much better, and indicate the underlying cause in more detail.

The I]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:

if (select(nfds, readfds, writefds, exceptfds, timeout) < 0)
{
    char message[3000];
    explain_message_select(message, sizeof(message),
        nfds, readfds, writefds, exceptfds, timeout);
    fprintf(stderr, "%s\n", message);
    exit(EXIT_FAILURE);
}

I]message
  The location in which to store the returned message. If a suitable message return buffer is supplied, this function is thread safe.
I]message_size
  The size in bytes of the location in which to store the returned message.
I]nfds The original nfds, exactly as passed to the I]select(2) system call.
I]readfds
  The original readfds, exactly as passed to the I]select(2) system call.
I]writefds
  The original writefds, exactly as passed to the I]select(2) system call.
I]exceptfds
  The original exceptfds, exactly as passed to the I]select(2) system call.
I]timeout
  The original timeout, exactly as passed to the I]select(2) system call.

    explain_message_errno_select

void explain_message_errno_select(char *message, int message_size, int errnum, int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout);

The B]explain_message_errno_select function may be used to obtain an explanation of an error returned by the I]select(2) system call. The least the message will contain is the value of CW]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:

if (select(nfds, readfds, writefds, exceptfds, timeout) < 0)
{
    int err = errno;
    char message[3000];
    explain_message_errno_select(message, sizeof(message), err,
        nfds, readfds, writefds, exceptfds, timeout);
    fprintf(stderr, "%s\n", message);
    exit(EXIT_FAILURE);
}

I]message
  The location in which to store the returned message. If a suitable message return buffer is supplied, this function is thread safe.
I]message_size
  The size in bytes of the location in which to store the returned message.
I]errnum The error value to be decoded, usually obtained from the I]errno global variable just before this function is called. This is necessary if you need to call B]any code between the system call to be explained and this function, because many libc functions will alter the value of I]errno.
I]nfds The original nfds, exactly as passed to the I]select(2) system call.
I]readfds
  The original readfds, exactly as passed to the I]select(2) system call.
I]writefds
  The original writefds, exactly as passed to the I]select(2) system call.
I]exceptfds
  The original exceptfds, exactly as passed to the I]select(2) system call.
I]timeout
  The original timeout, exactly as passed to the I]select(2) system call.

SEE ALSO

I]select(2)
  blah blah
I]explain_select_or_die(3)
  blah blah and report errors

COPYRIGHT

libexplain version 1.3
Copyright © 2008 Peter Miller
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