Provided by: libexplain-dev_1.4.D001-13_amd64 
NAME
explain_ftell - explain ftell(3) errors
SYNOPSIS
#include <libexplain/ftell.h>
const char *explain_ftell(FILE *fp);
const char *explain_errno_ftell(int errnum, FILE *fp);
void explain_message_ftell(char *message, int message_size, FILE *fp);
void explain_message_errno_ftell(char *message, int message_size, int errnum, FILE *fp);
DESCRIPTION
These functions may be used to obtain explanations for errors returned by the ftell(3) system call.
explain_ftell
const char *explain_ftell(FILE *fp);
The explain_ftell function is used to obtain an explanation of an error returned by the ftell(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 ftell(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:
long result = ftell(fp);
if (result < 0)
{
fprintf(stderr, "%s\n", explain_ftell(fp));
exit(EXIT_FAILURE);
}
The above code example is available pre‐packaged as the explain_ftell_or_die(3) function.
explain_errno_ftell
const char *explain_errno_ftell(int errnum, FILE *fp);
The explain_errno_ftell function is used to obtain an explanation of an error returned by the ftell(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 ftell(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:
long result = ftell(fp);
if (result < 0)
{
int err = errno;
fprintf(stderr, "%s\n", explain_errno_ftell(err, fp));
exit(EXIT_FAILURE);
}
The above code example is available pre‐packaged as the explain_ftell_or_die(3) function.
explain_message_ftell
void explain_message_ftell(char *message, int message_size, FILE *fp);
The explain_message_ftell function is used to obtain an explanation of an error returned by the ftell(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 ftell(3) system call.
Example: This function is intended to be used in a fashion similar to the following example:
long result = ftell(fp);
if (result < 0)
{
char message[3000];
explain_message_ftell(message, sizeof(message), fp);
fprintf(stderr, "%s\n", message);
exit(EXIT_FAILURE);
}
The above code example is available pre‐packaged as the explain_ftell_or_die(3) function.
explain_message_errno_ftell
void explain_message_errno_ftell(char *message, int message_size, int errnum, FILE *fp);
The explain_message_errno_ftell function is used to obtain an explanation of an error returned by the
ftell(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 ftell(3) system call.
Example: This function is intended to be used in a fashion similar to the following example:
long result = ftell(fp);
if (result < 0)
{
int err = errno;
char message[3000];
explain_message_errno_ftell(message, sizeof(message), err, fp);
fprintf(stderr, "%s\n", message);
exit(EXIT_FAILURE);
}
The above code example is available pre‐packaged as the explain_ftell_or_die(3) function.
SEE ALSO
ftell(3)
reposition a stream
explain_ftell_or_die(3)
reposition a stream and report errors
COPYRIGHT
libexplain version 1.4
Copyright (C) 2010 Peter Miller
explain_ftell(3)