explain_vsnprintf(3)

NAME
explain_vsnprintf - explain vsnprintf(3) errors

SYNOPSIS
#include <libexplain/vsnprintf.h>

const char *explain_vsnprintf(char *data, size_t data_size, const char *format, va_list ap);
const char *explain_errno_vsnprintf(int errnum, char *data, size_t data_size, const char *format, va_list ap);
void explain_message_vsnprintf(char *message, int message_size, char *data, size_t data_size, const char *format, va_list ap);
void explain_message_errno_vsnprintf(char *message, int message_size, int errnum, char *data, size_t data_size, const char *format, va_list ap);

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

  explain_vsnprintf
const char *explain_vsnprintf(char *data, size_t data_size, const char *format, va_list ap);

The explain_vsnprintf function is used to obtain an explanation of an error returned by the vsnprintf(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.

data
    The original data, exactly as passed to the vsnprintf(3) system call.

data_size
    The original data_size, exactly as passed to the vsnprintf(3) system call.

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

ap  The original ap, exactly as passed to the vsnprintf(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 = 0;
    int result = vsnprintf(data, data_size, format, ap);
    if (result < 0 && errno != 0)
    {
    fprintf(stderr, "%s\n", explain_vsnprintf(data, data_size, format, ap));
        exit(EXIT_FAILURE);
    }

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

  explain_errno_vsnprintf
const char *explain_errno_vsnprintf(int errnum, char *data, size_t data_size, const char *format, va_list ap);

The explain_errno_vsnprintf function is used to obtain an explanation of an error returned by the vsnprintf(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.

data
    The original data, exactly as passed to the vsnprintf(3) system call.

data_size
    The original data_size, exactly as passed to the vsnprintf(3) system call.

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

ap  The original ap, exactly as passed to the vsnprintf(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 = 0;
    int result = vsnprintf(data, data_size, format, ap);
    if (result < 0 && errno != 0)
    {
        int err = errno;
    fprintf(stderr, "%s\n", explain_errno_vsnprintf(err, data, data_size, format, ap));
        exit(EXIT_FAILURE);
    }

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

  explain_message_vsnprintf
void explain_message_vsnprintf(char *message, int message_size, char *data, size_t data_size, const char *format, va_list ap);

The explain_message_vsnprintf function is used to obtain an explanation of an error returned by the vsnprintf(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.

data
    The original data, exactly as passed to the vsnprintf(3) system call.

data_size
    The original data_size, exactly as passed to the vsnprintf(3) system call.

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

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

Example: This function is intended to be used in a fashion similar to the following example:
    errno = 0;
    int result = vsnprintf(data, data_size, format, ap);
    if (result < 0 && errno != 0)
    {
        char message[3000];
    explain_message_vsnprintf(message, sizeof(message), data, data_size, format, ap);
        fprintf(stderr, "%s\n", message);
        exit(EXIT_FAILURE);
    }

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

  explain_message_errno_vsnprintf
void explain_message_errno_vsnprintf(char *message, int message_size, int errnum, char *data, size_t data_size, const char *format, va_list ap);

The explain_message_errno_vsnprintf function is used to obtain an explanation of an error returned by the vsnprintf(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.

data
    The original data, exactly as passed to the vsnprintf(3) system call.

data_size
    The original data_size, exactly as passed to the vsnprintf(3) system call.

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

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

Example: This function is intended to be used in a fashion similar to the following example:
    errno = 0;
    int result = vsnprintf(data, data_size, format, ap);
    if (result < 0 && errno != 0)
    {
        int err = errno;
        char message[3000];
    explain_message_errno_vsnprintf(message, sizeof(message), err, data, data_size, format, ap);
        fprintf(stderr, "%s\n", message);
        exit(EXIT_FAILURE);
    }

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

SEE ALSO

vsnprintf(3)
    formatted output conversion

explain_vsnprintf_or_die(3)
    formatted output conversion and report errors

COPYRIGHT
libexplain version
Copyright (C) 2010 Peter Miller