libexplain/fprintf.h File Reference

explain fprintf(3) errors More...

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

Go to the source code of this file.

Functions
int	explain_fprintf_or_die (FILE *fp, const char *format,...) LIBEXPLAIN_FORMAT_PRINTF(2
int int	explain_fprintf_on_error (FILE *fp, const char *format,...) LIBEXPLAIN_FORMAT_PRINTF(2
int int const char *	explain_fprintf (FILE *fp, const char *format,...) LIBEXPLAIN_FORMAT_PRINTF(2
const char *	explain_errno_fprintf (int errnum, FILE *fp, const char *format,...) LIBEXPLAIN_FORMAT_PRINTF(3
void	explain_message_fprintf (char *message, int message_size, FILE *fp, const char *format,...) LIBEXPLAIN_FORMAT_PRINTF(4
void void	explain_message_errno_fprintf (char *message, int message_size, int errnum, FILE *fp, const char *format,...) LIBEXPLAIN_FORMAT_PRINTF(5
Variables
int int const char	LIBEXPLAIN_WARN_UNUSED_RESULT

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Detailed Description

explain fprintf(3) errors

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

Definition in file fprintf.h.

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Function Documentation

const char* explain_errno_fprintf	(	int	errnum,
		FILE *	fp,
		const char *	format,
			...
	)

The explain_errno_fprintf function is used to obtain an explanation of an error returned by the fprintf(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.
fp	The original fp, exactly as passed to the fprintf(3) system call.
format	The original format, exactly as passed to the fprintf(3) system call.
...	and then the arguments described by the format, exactly as passed to the fprintf(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 = fprintf(fp, format, ...);
 if (result < 0)
 {
     int err = errno;
     fprintf(stderr, "%s\n", explain_errno_fprintf(err, fp, format, ...));
     exit(EXIT_FAILURE);
 }

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

int int const char* explain_fprintf	(	FILE *	fp,
		const char *	format,
			...
	)

The explain_fprintf function is used to obtain an explanation of an error returned by the fprintf(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:

fp	The original fp, exactly as passed to the fprintf(3) system call.
format	The original format, exactly as passed to the fprintf(3) system call.
...	and then the arguments described by the format, exactly as passed to the fprintf(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 = fprintf(fp, format, ...);
 if (result < 0)
 {
     fprintf(stderr, "%s\n", explain_fprintf(fp, format, ...));
     exit(EXIT_FAILURE);
 }

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

int int explain_fprintf_on_error	(	FILE *	fp,
		const char *	format,
			...
	)

The explain_fprintf_on_error function is used to call the fprintf(3) system call. On failure an explanation will be printed to stderr, obtained from the explain_fprintf(3) function.

Parameters:

fp	The fp, exactly as to be passed to the fprintf(3) system call.
format	The format, exactly as to be passed to the fprintf(3) system call.
...	and then the arguments described by the format

Returns:

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

Example:

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

 int result = explain_fprintf_on_error(fp, format, ...);
 if (result < 0)
 {
     ...cope with error
     ...no need to print error message
 }

int explain_fprintf_or_die	(	FILE *	fp,
		const char *	format,
			...
	)

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

Parameters:

fp	The fp, exactly as to be passed to the fprintf(3) system call.
format	The format, exactly as to be passed to the fprintf(3) system call.
...	and then the arguments described by the format

Returns:

This function only returns on success, see fprintf(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_fprintf_or_die(fp, format, ...);

void void explain_message_errno_fprintf	(	char *	message,
		int	message_size,
		int	errnum,
		FILE *	fp,
		const char *	format,
			...
	)

The explain_message_errno_fprintf function is used to obtain an explanation of an error returned by the fprintf(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.
fp	The original fp, exactly as passed to the fprintf(3) system call.
format	The original format, exactly as passed to the fprintf(3) system call.
...	and then the arguments described by the format, exactly as passed to the fprintf(3) system call.

Example:

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

 errno = EINVAL;
 int result = fprintf(fp, format, ...);
 if (result < 0 && errno != 0)
 {
     int err = errno;
     char message[3000];
     explain_message_errno_fprintf(message, sizeof(message), err, fp,
         format, ...);
     fprintf(stderr, "%s\n", message);
     exit(EXIT_FAILURE);
 }

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

void explain_message_fprintf	(	char *	message,
		int	message_size,
		FILE *	fp,
		const char *	format,
			...
	)

The explain_message_fprintf function is used to obtain an explanation of an error returned by the fprintf(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.
fp	The original fp, exactly as passed to the fprintf(3) system call.
format	The original format, exactly as passed to the fprintf(3) system call.
...	and then the arguments described by the format, exactly as passed to the fprintf(3) system call.

Example:

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

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

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

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Variable Documentation

const char LIBEXPLAIN_WARN_UNUSED_RESULT

Definition at line 149 of file fprintf.h.