explain_snprintf(3)

NAME
explain_snprintf - explain snprintf(3) errors

SYNOPSIS
#include <libexplain/snprintf.h>

const char *explain_snprintf(char *data, size_t data_size, const char *format);
const char *explain_errno_snprintf(int errnum, char *data, size_t data_size, const char *format);
void explain_message_snprintf(char *message, int message_size, char *data, size_t data_size, const char *format);
void explain_message_errno_snprintf(char *message, int message_size, int errnum, char *data, size_t data_size, const char *format);

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

  explain_snprintf
const char *explain_snprintf(char *data, size_t data_size, const char *format);

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

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

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

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

  explain_errno_snprintf
const char *explain_errno_snprintf(int errnum, char *data, size_t data_size, const char *format);

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

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

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

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

  explain_message_snprintf
void explain_message_snprintf(char *message, int message_size, char *data, size_t data_size, const char *format);

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

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

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

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

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

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

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

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

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

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

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

SEE ALSO

snprintf(3)
    formatted output conversion

explain_snprintf_or_die(3)
    formatted output conversion and report errors

COPYRIGHT
libexplain version
Copyright (C) 2010 Peter Miller