Poster of Linux kernelThe best gift for a Linux geek
explain_fseek

explain_fseek

Section: C Library Functions (3)
Local index Up
 

NAME

explain_fseek - explain fseek(3) errors  

SYNOPSIS

#include <libexplain/fseek.h>

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

DESCRIPTION

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

explain_fseek

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.

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(3) function.  

explain_errno_fseek

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

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(3) function.  

explain_message_fseek

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(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.

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(3) function.  

explain_message_errno_fseek

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

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(3) function.  

SEE ALSO

fseek(3)
reposition a stream
explain_fseek_or_die(3)
reposition a stream and report errors
 

COPYRIGHT

libexplain version 0.37
Copyright (C) 2010 Peter Miller


 

Index

NAME
SYNOPSIS
DESCRIPTION
explain_fseek
explain_errno_fseek
explain_message_fseek
explain_message_errno_fseek
SEE ALSO
COPYRIGHT

This document was created by man2html, using the manual pages.
Time: 21:45:48 GMT, April 16, 2011