explain_fseeko man page

explain_fseeko — explain fseeko(3) errors

Synopsis

#include <libexplain/fseeko.h>

const char *explain_fseeko(FILE *fp, off_t offset, int whence);
const char *explain_errno_fseeko(int errnum, FILE *fp, off_t offset, int whence);
void explain_message_fseeko(char *message, int message_size, FILE *fp, off_t offset, int whence);
void explain_message_errno_fseeko(char *message, int message_size, int errnum, FILE *fp, off_t offset, int whence);

Description

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

explain_fseeko

const char *explain_fseeko(FILE *fp, off_t offset, int whence);

The explain_fseeko function is used to obtain an explanation of an error returned by the fseeko(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 fseeko(3) system call.
offset
The original offset, exactly as passed to the fseeko(3) system call.
whence
The original whence, exactly as passed to the fseeko(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:

if (fseeko(fp, offset, whence) < 0)

{

fprintf(stderr, "%s\n", explain_fseeko(fp, offset, whence));

    exit(EXIT_FAILURE);
}

The above code example is available pre-packaged as the explain_fseeko_or_die(3) function.

explain_errno_fseeko

const char *explain_errno_fseeko(int errnum, FILE *fp, off_t offset, int whence);

The explain_errno_fseeko function is used to obtain an explanation of an error returned by the fseeko(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 fseeko(3) system call.
offset
The original offset, exactly as passed to the fseeko(3) system call.
whence
The original whence, exactly as passed to the fseeko(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:

if (fseeko(fp, offset, whence) < 0)

{
    int err = errno;

fprintf(stderr, "%s\n", explain_errno_fseeko(err, fp, offset, whence));

    exit(EXIT_FAILURE);
}

The above code example is available pre-packaged as the explain_fseeko_or_die(3) function.

explain_message_fseeko

void explain_message_fseeko(char *message, int message_size, FILE *fp, off_t offset, int whence);

The explain_message_fseeko function is used to obtain an explanation of an error returned by the fseeko(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 fseeko(3) system call.
offset
The original offset, exactly as passed to the fseeko(3) system call.
whence
The original whence, exactly as passed to the fseeko(3) system call.

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

if (fseeko(fp, offset, whence) < 0)

{
    char message[3000];

explain_message_fseeko(message, sizeof(message), fp, offset, whence);

    fprintf(stderr, "%s\n", message);
    exit(EXIT_FAILURE);
}

The above code example is available pre-packaged as the explain_fseeko_or_die(3) function.

explain_message_errno_fseeko

void explain_message_errno_fseeko(char *message, int message_size, int errnum, FILE *fp, off_t offset, int whence);

The explain_message_errno_fseeko function is used to obtain an explanation of an error returned by the fseeko(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 fseeko(3) system call.
offset
The original offset, exactly as passed to the fseeko(3) system call.
whence
The original whence, exactly as passed to the fseeko(3) system call.

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

if (fseeko(fp, offset, whence) < 0)

{
    int err = errno;
    char message[3000];

explain_message_errno_fseeko(message, sizeof(message), err, fp, offset, whence);

    fprintf(stderr, "%s\n", message);
    exit(EXIT_FAILURE);
}

The above code example is available pre-packaged as the explain_fseeko_or_die(3) function.

See Also

fseeko(3)
seek to or report file position
explain_fseeko_or_die(3)
seek to or report file position and report errors

Referenced By

explain(3), explain_fseeko_or_die(3).