libexplain/gethostbyname.h File Reference

explain gethostbyname(3) errors More...

#include <libexplain/gcc_attributes.h>
#include <libexplain/large_file_support.h>

Go to the source code of this file.

Functions
struct hostent *	explain_gethostbyname_or_die (const char *name) LIBEXPLAIN_WARN_UNUSED_RESULT
struct hostent *	explain_gethostbyname_on_error (const char *name) LIBEXPLAIN_WARN_UNUSED_RESULT
const char *	explain_gethostbyname (const char *name) LIBEXPLAIN_WARN_UNUSED_RESULT
const char *	explain_errno_gethostbyname (int errnum, const char *name) LIBEXPLAIN_WARN_UNUSED_RESULT
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)

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Detailed Description

explain gethostbyname(3) errors

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

Definition in file gethostbyname.h.

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Function Documentation

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(errnum), but usually it will do much better, and indicate the underlying cause in more detail.

Parameters:

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 function.

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.

Parameters:

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 function.

struct hostent* explain_gethostbyname_on_error

(

const char *

name

)

[read]

The explain_gethostbyname_on_error function is used to call the gethostbyname(3) system call. On failure an explanation will be printed to stderr, obtained from the explain_gethostbyname(3) function.

Parameters:

name	The name, exactly as to be passed to the gethostbyname(3) system call.

Returns:

The value returned by the wrapped gethostbyname(3) system call.

Example:

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

 struct hostent *result = explain_gethostbyname_on_error(name);
 if (!result)
 {
     ...cope with error
     ...no need to print error message
 }

struct hostent* explain_gethostbyname_or_die

(

const char *

name

)

[read]

The explain_gethostbyname_or_die function is used to call the gethostbyname(3) system call. On failure an explanation will be printed to stderr, obtained from the explain_gethostbyname(3) function, and then the process terminates by calling exit(EXIT_FAILURE).

Parameters:

name	The name, exactly as to be passed to the gethostbyname(3) system call.

Returns:

This function only returns on success, see gethostbyname(3) for more information. On failure, prints an explanation and exits, it does not return.

Example:

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

 struct hostent *result = explain_gethostbyname_or_die(name);

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(errnum), but usually it will do much better, and indicate the underlying cause in more detail.

Parameters:

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 function.

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(errnum), 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.

Parameters:

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 function.