explain_ferror(3)

NAME
explain_ferror - explain ferror(3) errors

SYNOPSIS
#include <libexplain/ferror.h>

const char *explain_ferror(FILE *fp);
const char *explain_errno_ferror(int errnum, FILE *fp);
void explain_message_ferror(char *message, int message_size, FILE *fp);
void explain_message_errno_ferror(char *message, int message_size, int errnum, FILE *fp);

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

  explain_ferror
const char *explain_ferror(FILE *fp);

The explain_ferror function is used to obtain an explanation of an error returned by the ferror(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.

This function is intended to be used in a fashion similar to the following example:
    if (ferror(fp) < 0)
    {
        fprintf(stderr, "%s\n", explain_ferror(fp));
        exit(EXIT_FAILURE);
    }

It is essential that this function cal be placed as close as possible to the I/O code that has caused the problem, otherwise intervening code could have altered the errno global variable.

fp  The original fp, exactly as passed to the ferror(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.

  explain_errno_ferror
const char *explain_errno_ferror(int errnum, FILE *fp);

The explain_errno_ferror function is used to obtain an explanation of an error returned by the ferror(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.

This function is intended to be used in a fashion similar to the following example:
    if (ferror(fp) < 0)
    {
        int err = errno;
        fprintf(stderr, "%s\n", explain_errno_ferror(err, fp));
        exit(EXIT_FAILURE);
    }

It is essential that this function cal be placed as close as possible to the I/O code that has caused the problem, otherwise intervening code could have altered the errno global variable.

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 ferror(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.

  explain_message_ferror
void explain_message_ferror(char *message, int message_size, FILE *fp);

The explain_message_ferror function may be used to obtain an explanation of an error returned by the ferror(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.

This function is intended to be used in a fashion similar to the following example:
    if (ferror(fp) < 0)
    {
        char message[3000];
        explain_message_ferror(message, sizeof(message), fp);
        fprintf(stderr, "%s\n", message);
        exit(EXIT_FAILURE);
    }

It is essential that this function cal be placed as close as possible to the I/O code that has caused the problem, otherwise intervening code could have altered the errno global variable.

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 ferror(3) system call.

  explain_message_errno_ferror
void explain_message_errno_ferror(char *message, int message_size, int errnum, FILE *fp);

The explain_message_errno_ferror function may be used to obtain an explanation of an error returned by the ferror(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.

This function is intended to be used in a fashion similar to the following example:
    if (ferror(fp) < 0)
    {
        int err = errno;
        char message[3000];
        explain_message_errno_ferror(message, sizeof(message), err, fp);
        fprintf(stderr, "%s\n", message);
        exit(EXIT_FAILURE);
    }

It is essential that this function cal be placed as close as possible to the I/O code that has caused the problem, otherwise intervening code could have altered the errno global variable.

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 ferror(3) system call.

SEE ALSO

ferror(3)
    check stream status

explain_ferror_or_die(3)
    check stream status and report errors

COPYRIGHT
libexplain version 1.1
Copyright (C) 2008 Peter Miller