explain_vprintf(3) Library Functions Manual explain_vprintf(3)
NAME
explain_vprintf - explain vprintf(3) errors
SYNOPSIS
#include <libexplain/vprintf.h>
const char *explain_vprintf(const char *format, va_list ap);
const char *explain_errno_vprintf(int errnum, const char *format, va_list ap);
void explain_message_vprintf(char *message, int message_size, const char *format, va_list ap);
void explain_message_errno_vprintf(char *message, int message_size, int errnum, const char *format, va_list ap);
DESCRIPTION
These functions may be used to obtain explanations for errors returned by the vprintf(3) system call.
explain_vprintf
const char *explain_vprintf(const char *format, va_list ap);
The explain_vprintf function is used to obtain an explanation of an error returned by the vprintf(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.
format The original format, exactly as passed to the vprintf(3) system call.
ap The original ap, exactly as passed to the vprintf(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;
int result = vprintf(format, ap);
if (result < 0)
{
fprintf(stderr, "%s
", explain_vprintf(format, ap));
exit(EXIT_FAILURE);
}
The above code example is available pre-packaged as the explain_vprintf_or_die(3) function.
explain_errno_vprintf
const char *explain_errno_vprintf(int errnum, const char *format, va_list ap);
The explain_errno_vprintf function is used to obtain an explanation of an error returned by the vprintf(3) system call. The least the mes-
sage 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 neces-
sary 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.
format The original format, exactly as passed to the vprintf(3) system call.
ap The original ap, exactly as passed to the vprintf(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;
int result = vprintf(format, ap);
if (result < 0)
{
int err = errno;
fprintf(stderr, "%s
", explain_errno_vprintf(err, format, ap));
exit(EXIT_FAILURE);
}
The above code example is available pre-packaged as the explain_vprintf_or_die(3) function.
explain_message_vprintf
void explain_message_vprintf(char *message, int message_size, const char *format, va_list ap);
The explain_message_vprintf function is used to obtain an explanation of an error returned by the vprintf(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.
format The original format, exactly as passed to the vprintf(3) system call.
ap The original ap, exactly as passed to the vprintf(3) system call.
Example: This function is intended to be used in a fashion similar to the following example:
errno = EINVAL;
int result = vprintf(format, ap);
if (result < 0)
{
char message[3000];
explain_message_vprintf(message, sizeof(message), format, ap);
fprintf(stderr, "%s
", message);
exit(EXIT_FAILURE);
}
The above code example is available pre-packaged as the explain_vprintf_or_die(3) function.
explain_message_errno_vprintf
void explain_message_errno_vprintf(char *message, int message_size, int errnum, const char *format, va_list ap);
The explain_message_errno_vprintf function is used to obtain an explanation of an error returned by the vprintf(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 neces-
sary 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.
format The original format, exactly as passed to the vprintf(3) system call.
ap The original ap, exactly as passed to the vprintf(3) system call.
Example: This function is intended to be used in a fashion similar to the following example:
errno = EINVAL;
int result = vprintf(format, ap);
if (result < 0)
{
int err = errno;
char message[3000];
explain_message_errno_vprintf(message, sizeof(message), err, format, ap);
fprintf(stderr, "%s
", message);
exit(EXIT_FAILURE);
}
The above code example is available pre-packaged as the explain_vprintf_or_die(3) function.
SEE ALSO
vprintf(3)
formatted output conversion
explain_vprintf_or_die(3)
formatted output conversion and report errors
COPYRIGHT
libexplain version 0.52
Copyright (C) 2010 Peter Miller
explain_vprintf(3)