explain_gethostbyname man page

explain_gethostbyname — explain gethostbyname(3) errors

Synopsis

#include <libexplain/gethostbyname.h>

const char *explain_gethostbyname(const char *name);
const char *explain_errno_gethostbyname(int errnum, const char *name);
void explain_message_gethostbyname(char *message, int message_size, const char *name);
void explain_message_errno_gethostbyname(char *message, int message_size, int errnum, const char *name);

Description

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

explain_gethostbyname

const char *explain_gethostbyname(const char *name);

The explain_gethostbyname function is used to obtain an explanation of an error returned by the gethostbyname(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 gethostbyname(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:

struct hostent *result = gethostbyname(name);
if (!result)

{

fprintf(stderr, "%s\n", explain_gethostbyname(name));

    exit(EXIT_FAILURE);
}

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

explain_errno_gethostbyname

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

The explain_errno_gethostbyname function is used to obtain an explanation of an error returned by the gethostbyname(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 gethostbyname(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:

struct hostent *result = gethostbyname(name);
if (!result)

{
    int err = errno;

fprintf(stderr, "%s\n", explain_errno_gethostbyname(err, name));

    exit(EXIT_FAILURE);
}

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

explain_message_gethostbyname

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

The explain_message_gethostbyname function is used to obtain an explanation of an error returned by the gethostbyname(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 gethostbyname(3) system call.

Example: This function is intended to be used in a fashion similar to the following example:

struct hostent *result = gethostbyname(name);
if (!result)

{
    char message[3000];

explain_message_gethostbyname(message, sizeof(message), name);

    fprintf(stderr, "%s\n", message);
    exit(EXIT_FAILURE);
}

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

explain_message_errno_gethostbyname

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

The explain_message_errno_gethostbyname function is used to obtain an explanation of an error returned by the gethostbyname(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 gethostbyname(3) system call.

Example: This function is intended to be used in a fashion similar to the following example:

struct hostent *result = gethostbyname(name);
if (!result)

{
    int err = errno;
    char message[3000];

explain_message_errno_gethostbyname(message, sizeof(message), err, name);

    fprintf(stderr, "%s\n", message);
    exit(EXIT_FAILURE);
}

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

See Also

gethostbyname(3)
get host address given host name
explain_gethostbyname_or_die(3)
get host address given host name and report errors

Referenced By

explain(3), explain_gethostbyname_or_die(3).