libexplain/vsnprintf.h File Reference

explain vsnprintf(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_vsnprintf_or_die (char *data, size_t data_size, const char *format, va_list ap) LIBEXPLAIN_FORMAT_VPRINTF(3)
int	explain_vsnprintf_on_error (char *data, size_t data_size, const char *format, va_list ap) LIBEXPLAIN_FORMAT_VPRINTF(3)
const char *	explain_vsnprintf (char *data, size_t data_size, const char *format, va_list ap) LIBEXPLAIN_WARN_UNUSED_RESULT
const char *	explain_errno_vsnprintf (int errnum, char *data, size_t data_size, const char *format, va_list ap) LIBEXPLAIN_WARN_UNUSED_RESULT
void	explain_message_vsnprintf (char *message, int message_size, char *data, size_t data_size, const char *format, va_list ap) LIBEXPLAIN_FORMAT_VPRINTF(5)
void	explain_message_errno_vsnprintf (char *message, int message_size, int errnum, char *data, size_t data_size, const char *format, va_list ap) LIBEXPLAIN_FORMAT_VPRINTF(6)

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Detailed Description

explain vsnprintf(3) errors

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

Definition in file vsnprintf.h.

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Function Documentation

const char* explain_errno_vsnprintf	(	int	errnum,
		char *	data,
		size_t	data_size,
		const char *	format,
		va_list	ap
	)

The explain_errno_vsnprintf function is used to obtain an explanation of an error returned by the vsnprintf(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.
data	The original data, exactly as passed to the vsnprintf(3) system call.
data_size	The original data_size, exactly as passed to the vsnprintf(3) system call.
format	The original format, exactly as passed to the vsnprintf(3) system call.
ap	The original ap, exactly as passed to the vsnprintf(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 = 0;
 int result = vsnprintf(data, data_size, format, ap);
 if (result < 0 && errno != 0)
 {
     int err = errno;
     fprintf(stderr, "%s\n", explain_errno_vsnprintf(err, data, data_size,
         format, ap));
     exit(EXIT_FAILURE);
 }

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

void explain_message_errno_vsnprintf	(	char *	message,
		int	message_size,
		int	errnum,
		char *	data,
		size_t	data_size,
		const char *	format,
		va_list	ap
	)

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

Example:

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

 errno = 0;
 int result = vsnprintf(data, data_size, format, ap);
 if (result < 0 && errno != 0)
 {
     int err = errno;
     char message[3000];
     explain_message_errno_vsnprintf(message, sizeof(message), err, data,
         data_size, format, ap);
     fprintf(stderr, "%s\n", message);
     exit(EXIT_FAILURE);
 }

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

void explain_message_vsnprintf	(	char *	message,
		int	message_size,
		char *	data,
		size_t	data_size,
		const char *	format,
		va_list	ap
	)

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

Example:

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

 errno = 0;
 int result = vsnprintf(data, data_size, format, ap);
 if (result < 0 && errno != 0)
 {
     char message[3000];
     explain_message_vsnprintf(message, sizeof(message), data, data_size,
         format, ap);
     fprintf(stderr, "%s\n", message);
     exit(EXIT_FAILURE);
 }

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

const char* explain_vsnprintf	(	char *	data,
		size_t	data_size,
		const char *	format,
		va_list	ap
	)

The explain_vsnprintf function is used to obtain an explanation of an error returned by the vsnprintf(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:

data	The original data, exactly as passed to the vsnprintf(3) system call.
data_size	The original data_size, exactly as passed to the vsnprintf(3) system call.
format	The original format, exactly as passed to the vsnprintf(3) system call.
ap	The original ap, exactly as passed to the vsnprintf(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 = 0;
 int result = vsnprintf(data, data_size, format, ap);
 if (result < 0 && errno != 0)
 {
     fprintf(stderr, "%s\n", explain_vsnprintf(data, data_size, format, ap));
     exit(EXIT_FAILURE);
 }

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

int explain_vsnprintf_on_error	(	char *	data,
		size_t	data_size,
		const char *	format,
		va_list	ap
	)

The explain_vsnprintf_on_error function is used to call the vsnprintf(3) system call. On failure an explanation will be printed to stderr, obtained from the explain_vsnprintf(3) function.

Parameters:

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

Returns:

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

Example:

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

 errno = 0;
 int result = explain_vsnprintf_on_error(data, data_size, format, ap);
 if (result < 0 && errno != 0)
 {
     ...cope with error
     ...no need to print error message
 }

int explain_vsnprintf_or_die	(	char *	data,
		size_t	data_size,
		const char *	format,
		va_list	ap
	)

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

Parameters:

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

Returns:

This function only returns on success, see vsnprintf(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_vsnprintf_or_die(data, data_size, format, ap);