libexplain/fread.h File Reference

explain fread(3) errors More...

#include <libexplain/gcc_attributes.h>
#include <libexplain/large_file_support.h>
#include <stdio.h>

Go to the source code of this file.

Functions
size_t	explain_fread_or_die (void *ptr, size_t size, size_t nmemb, FILE *fp)
size_t	explain_fread_on_error (void *ptr, size_t size, size_t nmemb, FILE *fp) LIBEXPLAIN_WARN_UNUSED_RESULT
const char *	explain_fread (void *ptr, size_t size, size_t nmemb, FILE *fp) LIBEXPLAIN_WARN_UNUSED_RESULT
const char *	explain_errno_fread (int errnum, void *ptr, size_t size, size_t nmemb, FILE *fp) LIBEXPLAIN_WARN_UNUSED_RESULT
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)

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Detailed Description

explain fread(3) errors

Definition in file fread.h.

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Function Documentation

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:

 if (fread(ptr, size, nmemb, fp) == 0 && ferror(fp))
 {
     int err = errno;
     fprintf(stderr, "%s\n", explain_errno_fread(err, ptr, size, nmemb, fp));
     exit(EXIT_FAILURE);
 }

The above code example is available pre-packaged as the explain_fread_or_die function.

Parameters:

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.

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:

 if (fread(ptr, size, nmemb, fp) == 0 && ferror(fp))
 {
     fprintf(stderr, "%s\n", explain_fread(ptr, size, nmemb, fp));
     exit(EXIT_FAILURE);
 }

The above code example is available pre-packaged as the explain_fread_or_die function.

Parameters:

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.

size_t explain_fread_on_error	(	void *	ptr,
		size_t	size,
		size_t	nmemb,
		FILE *	fp
	)

The explain_fread_on_error function is used to call the fread(3) system call. On failure an explanation will be printed to stderr, obtained from the explain_fread(3) function.

This function is intended to be used in a fashion similar to the following example:

 if (explain_fread_on_error(ptr, size, nmemb, fp) == 0 && ferror(fp))
 {
     ...cope with error
     ...no need to print error message
 }

Parameters:

ptr	The ptr, exactly as to be passed to the fread(3) system call.
size	The size, exactly as to be passed to the fread(3) system call.
nmemb	The nmemb, exactly as to be passed to the fread(3) system call.
fp	The fp, exactly as to be passed to the fread(3) system call.

Returns:

The value returned by the wrapped fread(3) system call.

size_t explain_fread_or_die	(	void *	ptr,
		size_t	size,
		size_t	nmemb,
		FILE *	fp
	)

The explain_fread_or_die function is used to call the fread(3) system call. On failure an explanation will be printed to stderr, obtained from the explain_fread(3) function, and then the process terminates by calling exit(EXIT_FAILURE).

This function is intended to be used in a fashion similar to the following example:

 explain_fread_or_die(ptr, size, nmemb, fp);

Parameters:

ptr	The ptr, exactly as to be passed to the fread(3) system call.
size	The size, exactly as to be passed to the fread(3) system call.
nmemb	The nmemb, exactly as to be passed to the fread(3) system call.
fp	The fp, exactly as to be passed to the fread(3) system call.

Returns:

This function only returns on success. On failure, prints an explanation and exits, it does not return.

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 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:

 if (fread(ptr, size, nmemb, fp) == 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);
 }

The above code example is available pre-packaged as the explain_fread_or_die function.

Parameters:

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.

void explain_message_fread	(	char *	message,
		int	message_size,
		void *	ptr,
		size_t	size,
		size_t	nmemb,
		FILE *	fp
	)

The explain_message_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.

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 (fread(ptr, size, nmemb, fp) == 0 && ferror(fp))
 {
     char message[3000];
     explain_message_fread(message, sizeof(message), ptr, size, nmemb, fp);
     fprintf(stderr, "%s\n", message);
     exit(EXIT_FAILURE);
 }

The above code example is available pre-packaged as the explain_fread_or_die function.

Parameters:

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.