libexplain/fseek.h File Reference

explain fseek(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
void	explain_fseek_or_die (FILE *fp, long offset, int whence)
int	explain_fseek_on_error (FILE *fp, long offset, int whence)
const char *	explain_fseek (FILE *fp, long offset, int whence) LIBEXPLAIN_WARN_UNUSED_RESULT
const char *	explain_errno_fseek (int errnum, FILE *fp, long offset, int whence) LIBEXPLAIN_WARN_UNUSED_RESULT
void	explain_message_fseek (char *message, int message_size, FILE *fp, long offset, int whence)
void	explain_message_errno_fseek (char *message, int message_size, int errnum, FILE *fp, long offset, int whence)

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Detailed Description

explain fseek(3) errors

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

Definition in file fseek.h.

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Function Documentation

const char* explain_errno_fseek	(	int	errnum,
		FILE *	fp,
		long	offset,
		int	whence
	)

The explain_errno_fseek function is used to obtain an explanation of an error returned by the fseek(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 fseek(3) system call.
offset	The original offset, exactly as passed to the fseek(3) system call.
whence	The original whence, exactly as passed to the fseek(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:

 if (fseek(fp, offset, whence) < 0)
 {
     int err = errno;
     fprintf(stderr, "%s\n", explain_errno_fseek(err, fp, offset, whence));
     exit(EXIT_FAILURE);
 }

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

const char* explain_fseek	(	FILE *	fp,
		long	offset,
		int	whence
	)

The explain_fseek function is used to obtain an explanation of an error returned by the fseek(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 fseek(3) system call.
offset	The original offset, exactly as passed to the fseek(3) system call.
whence	The original whence, exactly as passed to the fseek(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:

 if (fseek(fp, offset, whence) < 0)
 {
     fprintf(stderr, "%s\n", explain_fseek(fp, offset, whence));
     exit(EXIT_FAILURE);
 }

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

int explain_fseek_on_error	(	FILE *	fp,
		long	offset,
		int	whence
	)

The explain_fseek_on_error function is used to call the fseek(3) system call. On failure an explanation will be printed to stderr, obtained from the explain_fseek(3) function.

Parameters:

fp	The fp, exactly as to be passed to the fseek(3) system call.
offset	The offset, exactly as to be passed to the fseek(3) system call.
whence	The whence, exactly as to be passed to the fseek(3) system call.

Returns:

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

Example:

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

 if (explain_fseek_on_error(fp, offset, whence) < 0)
 {
     ...cope with error
     ...no need to print error message
 }

void explain_fseek_or_die	(	FILE *	fp,
		long	offset,
		int	whence
	)

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

Parameters:

fp	The fp, exactly as to be passed to the fseek(3) system call.
offset	The offset, exactly as to be passed to the fseek(3) system call.
whence	The whence, exactly as to be passed to the fseek(3) system call.

Returns:

This function only returns on success, see fseek(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:

 explain_fseek_or_die(fp, offset, whence);

void explain_message_errno_fseek	(	char *	message,
		int	message_size,
		int	errnum,
		FILE *	fp,
		long	offset,
		int	whence
	)

The explain_message_errno_fseek function is used to obtain an explanation of an error returned by the fseek(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 fseek(3) system call.
offset	The original offset, exactly as passed to the fseek(3) system call.
whence	The original whence, exactly as passed to the fseek(3) system call.

Example:

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

 if (fseek(fp, offset, whence) < 0)
 {
     int err = errno;
     char message[3000];
     explain_message_errno_fseek(message, sizeof(message), err, fp, offset,
         whence);
     fprintf(stderr, "%s\n", message);
     exit(EXIT_FAILURE);
 }

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

void explain_message_fseek	(	char *	message,
		int	message_size,
		FILE *	fp,
		long	offset,
		int	whence
	)

The explain_message_fseek function is used to obtain an explanation of an error returned by the fseek(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 fseek(3) system call.
offset	The original offset, exactly as passed to the fseek(3) system call.
whence	The original whence, exactly as passed to the fseek(3) system call.

Example:

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

 if (fseek(fp, offset, whence) < 0)
 {
     char message[3000];
     explain_message_fseek(message, sizeof(message), fp, offset, whence);
     fprintf(stderr, "%s\n", message);
     exit(EXIT_FAILURE);
 }

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