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 0.52
Copyright (C) 2008 Peter Miller