SYNOPSIS

#include <libexplain/vfprintf.h>

const char *explain_vfprintf(FILE *fp, const char *format, va_list ap);
const char *explain_errno_vfprintf(int errnum, FILE *fp, const char *format, va_list ap);
void explain_message_vfprintf(char *message, int message_size, FILE *fp, const char *format, va_list ap);
void explain_message_errno_vfprintf(char *message, int message_size, int errnum, FILE *fp, const char *format, va_list ap);

DESCRIPTION

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

explain_vfprintf

const char *explain_vfprintf(FILE *fp, const char *format, va_list ap);

The explain_vfprintf function is used to obtain an explanation of an error returned by the vfprintf(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 vfprintf(3) system call.

format

The original format, exactly as passed to the vfprintf(3) system call.

ap

The original ap, exactly as passed to the vfprintf(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:

errno = EINVAL; if (vfprintf(fp, format, ap) < 0)

{

fprintf(stderr, "%s\n", explain_vfprintf(fp, format, ap));

    exit(EXIT_FAILURE);
}

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

explain_errno_vfprintf

const char *explain_errno_vfprintf(int errnum, FILE *fp, const char *format, va_list ap);

The explain_errno_vfprintf function is used to obtain an explanation of an error returned by the vfprintf(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 vfprintf(3) system call.

format

The original format, exactly as passed to the vfprintf(3) system call.

ap

The original ap, exactly as passed to the vfprintf(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:

errno = EINVAL; if (vfprintf(fp, format, ap) < 0)

{
    int err = errno;

fprintf(stderr, "%s\n", explain_errno_vfprintf(err, fp, format, ap));

    exit(EXIT_FAILURE);
}

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

explain_message_vfprintf

void explain_message_vfprintf(char *message, int message_size, FILE *fp, const char *format, va_list ap);

The explain_message_vfprintf function is used to obtain an explanation of an error returned by the vfprintf(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 vfprintf(3) system call.

format

The original format, exactly as passed to the vfprintf(3) system call.

ap

The original ap, exactly as passed to the vfprintf(3) system call.

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

errno = EINVAL; if (vfprintf(fp, format, ap) < 0)

{
    char message[3000];

explain_message_vfprintf(message, sizeof(message), fp, format, ap);

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

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

explain_message_errno_vfprintf

void explain_message_errno_vfprintf(char *message, int message_size, int errnum, FILE *fp, const char *format, va_list ap);

The explain_message_errno_vfprintf function is used to obtain an explanation of an error returned by the vfprintf(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 vfprintf(3) system call.

format

The original format, exactly as passed to the vfprintf(3) system call.

ap

The original ap, exactly as passed to the vfprintf(3) system call.

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

errno = EINVAL; if (vfprintf(fp, format, ap) < 0)

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

explain_message_errno_vfprintf(message, sizeof(message), err, fp, format, ap);

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

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

COPYRIGHT

libexplain version 1.4
Copyright (C) 2010 Peter Miller