libexplain/vprintf.h File Reference

explain vprintf(3) errors More...

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

Go to the source code of this file.

Functions
int	explain_vprintf_or_die (const char *format, va_list ap) LIBEXPLAIN_FORMAT_VPRINTF(1)
int	explain_vprintf_on_error (const char *format, va_list ap) LIBEXPLAIN_FORMAT_VPRINTF(1)
const char *	explain_vprintf (const char *format, va_list ap) LIBEXPLAIN_FORMAT_VPRINTF(1) LIBEXPLAIN_WARN_UNUSED_RESULT
const char *	explain_errno_vprintf (int errnum, const char *format, va_list ap) LIBEXPLAIN_FORMAT_VPRINTF(2) LIBEXPLAIN_WARN_UNUSED_RESULT
void	explain_message_vprintf (char *message, int message_size, const char *format, va_list ap) LIBEXPLAIN_FORMAT_VPRINTF(3)
void	explain_message_errno_vprintf (char *message, int message_size, int errnum, const char *format, va_list ap) LIBEXPLAIN_FORMAT_VPRINTF(4)

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Detailed Description

explain vprintf(3) errors

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

Definition in file vprintf.h.

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Function Documentation

const char* explain_errno_vprintf	(	int	errnum,
		const char *	format,
		va_list	ap
	)

The explain_errno_vprintf function is used to obtain an explanation of an error returned by the vprintf(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.
format	The original format, exactly as passed to the vprintf(3) system call.
ap	The original ap, exactly as passed to the vprintf(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:

 errno = EINVAL;
 int result = vprintf(format, ap);
 if (result < 0)
 {
     int err = errno;
     fprintf(stderr, "%s\n", explain_errno_vprintf(err, format, ap));
     exit(EXIT_FAILURE);
 }

The above code example is available pre-packaged as the explain_vprintf_or_die function.

void explain_message_errno_vprintf	(	char *	message,
		int	message_size,
		int	errnum,
		const char *	format,
		va_list	ap
	)

The explain_message_errno_vprintf function is used to obtain an explanation of an error returned by the vprintf(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.
format	The original format, exactly as passed to the vprintf(3) system call.
ap	The original ap, exactly as passed to the vprintf(3) system call.

Example:

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

 errno = EINVAL;
 int result = vprintf(format, ap);
 if (result < 0)
 {
     int err = errno;
     char message[3000];
     explain_message_errno_vprintf(message, sizeof(message), err, format,
         ap);
     fprintf(stderr, "%s\n", message);
     exit(EXIT_FAILURE);
 }

The above code example is available pre-packaged as the explain_vprintf_or_die function.

void explain_message_vprintf	(	char *	message,
		int	message_size,
		const char *	format,
		va_list	ap
	)

The explain_message_vprintf function is used to obtain an explanation of an error returned by the vprintf(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.
format	The original format, exactly as passed to the vprintf(3) system call.
ap	The original ap, exactly as passed to the vprintf(3) system call.

Example:

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

 errno = EINVAL;
 int result = vprintf(format, ap);
 if (result < 0)
 {
     char message[3000];
     explain_message_vprintf(message, sizeof(message), format, ap);
     fprintf(stderr, "%s\n", message);
     exit(EXIT_FAILURE);
 }

The above code example is available pre-packaged as the explain_vprintf_or_die function.

const char* explain_vprintf	(	const char *	format,
		va_list	ap
	)

The explain_vprintf function is used to obtain an explanation of an error returned by the vprintf(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:

format	The original format, exactly as passed to the vprintf(3) system call.
ap	The original ap, exactly as passed to the vprintf(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:

 errno = EINVAL;
 int result = vprintf(format, ap);
 if (result < 0)
 {
     fprintf(stderr, "%s\n", explain_vprintf(format, ap));
     exit(EXIT_FAILURE);
 }

The above code example is available pre-packaged as the explain_vprintf_or_die function.

int explain_vprintf_on_error	(	const char *	format,
		va_list	ap
	)

The explain_vprintf_on_error function is used to call the vprintf(3) system call. On failure an explanation will be printed to stderr, obtained from the explain_vprintf(3) function.

Parameters:

format	The format, exactly as to be passed to the vprintf(3) system call.
ap	The ap, exactly as to be passed to the vprintf(3) system call.

Returns:

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

Example:

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

 errno = EINVAL;
 int result = explain_vprintf_on_error(format, ap);
 if (result < 0)
 {
     ...cope with error
     ...no need to print error message
 }

int explain_vprintf_or_die	(	const char *	format,
		va_list	ap
	)

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

Parameters:

format	The format, exactly as to be passed to the vprintf(3) system call.
ap	The ap, exactly as to be passed to the vprintf(3) system call.

Returns:

This function only returns on success, see vprintf(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:

 int result = explain_vprintf_or_die(format, ap);