explain_fread(3)

NAME
explain_fread - explain fread(3) errors

SYNOPSIS
#include <libexplain/fread.h>

const char *explain_fread(void *ptr, size_t size, size_t nmemb, FILE *fp);
const char *explain_errno_fread(int errnum, void *ptr, size_t size, size_t nmemb, FILE *fp);
void explain_message_fread(char *message, int message_size, void *ptr, size_t size, size_t nmemb, FILE *fp);
void explain_message_errno_fread(char *message, int message_size, int errnum, void *ptr, size_t size, size_t nmemb, FILE *fp);

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

  explain_fread
const char *explain_fread(void *ptr, size_t size, size_t nmemb, FILE *fp);

The explain_fread function is used to obtain an explanation of an error returned by the fread(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:
    size_t how_many = fread(ptr, size, nmemb, fp);
    if (how_many == 0 && ferror(fp))
    {
        fprintf(stderr, "%s\n", explain_fread(ptr, size, nmemb, fp));
        exit(EXIT_FAILURE);
    }

ptr The original ptr, exactly as passed to the fread(3) system call.

size
    The original size, exactly as passed to the fread(3) system call.

nmemb
    The original nmemb, exactly as passed to the fread(3) system call.

fp  The original fp, exactly as passed to the fread(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_fread
const char *explain_errno_fread(int errnum, void *ptr, size_t size, size_t nmemb, FILE *fp);

The explain_errno_fread function is used to obtain an explanation of an error returned by the fread(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:
    size_t how_many = fread(ptr, size, nmemb, fp);
    if (how_many == 0 && ferror(fp))
    {
        int err = errno;
        fprintf(stderr, "%s\n", explain_errno_fread(err, ptr, size, nmemb, fp));
        exit(EXIT_FAILURE);
    }

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.

ptr The original ptr, exactly as passed to the fread(3) system call.

size
    The original size, exactly as passed to the fread(3) system call.

nmemb
    The original nmemb, exactly as passed to the fread(3) system call.

fp  The original fp, exactly as passed to the fread(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_fread
void explain_message_fread(char *message, int message_size, void *ptr, size_t size, size_t nmemb, FILE *fp);

The explain_message_fread function may be used to obtain an explanation of an error returned by the fread(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:
    size_t how_many = fread(ptr, size, nmemb, fp);
    if (how_many == 0 && ferror(fp))
    {
        char message[3000];
        explain_message_fread(message, sizeof(message), ptr, size, nmemb, fp);
        fprintf(stderr, "%s\n", message);
        exit(EXIT_FAILURE);
    }

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.

ptr The original ptr, exactly as passed to the fread(3) system call.

size
    The original size, exactly as passed to the fread(3) system call.

nmemb
    The original nmemb, exactly as passed to the fread(3) system call.

fp  The original fp, exactly as passed to the fread(3) system call.

  explain_message_errno_fread
void explain_message_errno_fread(char *message, int message_size, int errnum, void *ptr, size_t size, size_t nmemb, FILE *fp);

The explain_message_errno_fread function may be used to obtain an explanation of an error returned by the fread(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:
    size_t how_many = fread(ptr, size, nmemb, fp);
    if (how_many == 0 && ferror(fp))
    {
        int err = errno;
        char message[3000];
        explain_message_errno_fread(message, sizeof(message), err,
            ptr, size, nmemb, fp);
        fprintf(stderr, "%s\n", message);
        exit(EXIT_FAILURE);
    }

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.

ptr The original ptr, exactly as passed to the fread(3) system call.

size
    The original size, exactly as passed to the fread(3) system call.

nmemb
    The original nmemb, exactly as passed to the fread(3) system call.

fp  The original fp, exactly as passed to the fread(3) system call.

SEE ALSO

fread(3)
    binary stream input

explain_fread_or_die(3)
    binary stream input and report errors

COPYRIGHT
libexplain version
Copyright (C) 2008 Peter Miller