NAME¶

std::vwscanf,std::vfwscanf,std::vswscanf - std::vwscanf,std::vfwscanf,std::vswscanf

Synopsis¶

Defined in header <cwchar>
int vwscanf( const wchar_t* format, std::va_list vlist ); (1) (since C++11)
int vfwscanf( std::FILE* stream, const wchar_t* format, (2) (since C++11)
std::va_list vlist );
int vswscanf( const wchar_t* buffer, const wchar_t* format, (3) (since C++11)
std::va_list vlist );

Reads data from the a variety of sources, interprets it according to format and
stores the results into locations defined by vlist.

1) Reads the data from stdin.
2) Reads the data from file stream stream.
3) Reads the data from null-terminated wide string buffer.

Parameters¶

stream - input file stream to read from
buffer - pointer to a null-terminated wide string to read from
format - pointer to a null-terminated wide string specifying how to read the input
vlist - variable argument list containing the receiving arguments.

The format string consists of

* non-whitespace wide characters except %: each such character in the format
string consumes exactly one identical character from the input stream, or causes
the function to fail if the next character on the stream does not compare equal.
* whitespace characters: any single whitespace character in the format string
consumes all available consecutive whitespace characters from the input
(determined as if by calling iswspace in a loop). Note that there is no
difference between "\n", " ", "\t\t", or other whitespace in the format string.
* conversion specifications. Each conversion specification has the following
format:

* introductory % character.

* (optional) assignment-suppressing character *. If this option is present, the
function does not assign the result of the conversion to any receiving argument.

* (optional) integer number (greater than zero) that specifies maximum field
width, that is, the maximum number of characters that the function is allowed to
consume when doing the conversion specified by the current conversion
specification. Note that %s and %[ may lead to buffer overflow if the width is
not provided.

* (optional) length modifier that specifies the size of the receiving argument,
that is, the actual destination type. This affects the conversion accuracy and
overflow rules. The default destination type is different for each conversion
type (see table below).

* conversion format specifier.

The following format specifiers are available:

Conversion Explanation Argument type specifier
hh ll j z t
Length modifier → h (none) l L
(C++11) (C++11) (C++11) (C++11) (C++11)
% Matches literal %. N/A N/A N/A N/A N/A N/A N/A N/A N/A
Matches a character or
a sequence of
characters.

If a width specifier
is used, matches
exactly width wide
c characters (the
argument must be a
pointer to an array
with sufficient room).
Unlike %s and %[, does
not append the null
character to the
array.
Matches a sequence of
non-whitespace
characters (a string).

If width specifier is
used, matches up to
width or until the
first whitespace
s character, whichever
appears first. Always
stores a null
character in addition
to the characters
matched (so the
argument array must
have room for at least
width+1 characters) N/A N/A char* wchar_t* N/A N/A N/A N/A N/A
Matches a non-empty
sequence of character
from set of
characters.

If the first character
of the set is ^, then
all characters not in
the set are matched.
If the set begins with
] or ^] then the ]
character is also
included into the set.
It is
implementation-defined
[set] whether the character
- in the non-initial
position in the
scanset may be
indicating a range, as
in [0-9]. If width
specifier is used,
matches only up to
width. Always stores a
null character in
addition to the
characters matched (so
the argument array
must have room for at
least width+1
characters)
Matches a decimal
integer.

d The format of the
number is the same as
expected by wcstol
with the value 10 for
the base argument
Matches an integer.

The format of the
number is the same as
i expected by wcstol
with the value 0 for
the base argument
(base is determined by
the first characters
parsed)
Matches an unsigned
decimal integer.

u The format of the
number is the same as
expected by wcstoul signed
with the value 10 for signed signed signed signed long
the base argument. char* or short* int* or long* or long* or intmax_t*
Matches an unsigned unsigned or unsigned unsigned unsigned or size_t* ptrdiff_t* N/A
octal integer. char* unsigned int* long* long uintmax_t*
short* long*
o The format of the
number is the same as
expected by wcstoul
with the value 8 for
the base argument
Matches an unsigned
hexadecimal integer.

x, X The format of the
number is the same as
expected by wcstoul
with the value 16 for
the base argument
Returns the number of
characters read so
far.

No input is consumed.
n Does not increment the
assignment count. If
the specifier has
assignment-suppressing
operator defined, the
behavior is undefined
a, Matches a
A(C++11) floating-point number.
e, E N/A N/A float* double* N/A N/A N/A N/A long
f, F The format of the double*
g, G number is the same as
expected by wcstof
Matches implementation
defined character
sequence defining a
pointer.
p N/A N/A void** N/A N/A N/A N/A N/A N/A
printf family of
functions should
produce the same
sequence using %p
format specifier

For every conversion specifier other than n, the longest sequence of input
characters which does not exceed any specified field width and which either is
exactly what the conversion specifier expects or is a prefix of a sequence it would
expect, is what's consumed from the stream. The first character, if any, after this
consumed sequence remains unread. If the consumed sequence has length zero or if the
consumed sequence cannot be converted as specified above, the matching failure
occurs unless end-of-file, an encoding error, or a read error prevented input from
the stream, in which case it is an input failure.

All conversion specifiers other than [, c, and n consume and discard all leading
whitespace characters (determined as if by calling iswspace) before attempting to
parse the input. These consumed characters do not count towards the specified
maximum field width.

If the length specifier l is not used, the conversion specifiers c, s, and [ perform
wide-to-multibyte character conversion as if by calling wcrtomb with an mbstate_t
object initialized to zero before the first character is converted.

The conversion specifiers s and [ always store the null terminator in addition to
the matched characters. The size of the destination array must be at least one
greater than the specified field width. The use of %s or %[, without specifying the
destination array size, is as unsafe as std::gets.

The correct conversion specifications for the fixed-width integer types (int8_t,
etc) are defined in the header <cinttypes> (although SCNdMAX, SCNuMAX, etc is
synonymous with %jd, %ju, etc).

There is a sequence point after the action of each conversion specifier; this
permits storing multiple fields in the same "sink" variable.

When parsing an incomplete floating-point value that ends in the exponent with no
digits, such as parsing "100er" with the conversion specifier %f, the sequence
"100e" (the longest prefix of a possibly valid floating-point number) is consumed,
resulting in a matching error (the consumed sequence cannot be converted to a
floating-point number), with "r" remaining. Some existing implementations do not
follow this rule and roll back to consume only "100", leaving "er", e.g. glibc bug
1765.

Return value¶

Number of arguments successfully read, or EOF if failure occurs.

Example¶

This section is incomplete
Reason: no example

See also¶

wscanf reads formatted wide character input from stdin, a file stream or a buffer
fwscanf (function)
swscanf
C documentation for
vwscanf,
vfwscanf,
vswscanf

Category:¶

* Todo no example