Originální popis anglicky:
fwscanf, swscanf, wscanf - convert formatted wide-character input
Návod, kniha: POSIX Programmer's Manual
#include <stdio.h>
#include <wchar.h>
int fwscanf(FILE *restrict
stream, const wchar_t
*restrict format, ... );
int swscanf(const wchar_t *restrict
ws,
const wchar_t *restrict
format, ... );
int wscanf(const wchar_t *restrict
format, ... );
The
fwscanf() function shall read from the named input
stream. The
wscanf() function shall read from the standard input stream
stdin. The
swscanf() function shall read from the wide-character
string
ws. Each function reads wide characters, interprets them
according to a format, and stores the results in its arguments. Each expects,
as arguments, a control wide-character string
format described below,
and a set of
pointer arguments indicating where the converted input
should be stored. The result is undefined if there are insufficient arguments
for the format. If the
format is exhausted while arguments remain, the
excess arguments are evaluated but are otherwise ignored.
Conversions can be applied to the
nth argument after the
format in
the argument list, rather than to the next unused argument. In this case, the
conversion specifier wide character
% (see below) is replaced by the
sequence
"%n$" , where
n is a decimal integer in the
range [1,{NL_ARGMAX}]. This feature provides for the definition of
format wide-character strings that select arguments in an order
appropriate to specific languages. In
format wide-character strings
containing the
"%n$" form of conversion
specifications, it is unspecified whether numbered arguments in the argument
list can be referenced from the
format wide-character string more than
once.
The
format can contain either form of a conversion specification-that is,
% or
"%n$"- but the two forms cannot
normally be mixed within a single
format wide-character string. The
only exception to this is that
%% or
%* can be mixed with the
"%n$" form. When numbered argument
specifications are used, specifying the
Nth argument requires that all
the leading arguments, from the first to the (
N-1)th, are pointers.
The
fwscanf() function in all its forms allows for detection of a
language-dependent radix character in the input string, encoded as a
wide-character value. The radix character is defined in the program's locale
(category
LC_NUMERIC ). In the POSIX locale, or in a locale where the
radix character is not defined, the radix character shall default to a period
(
'.' ).
The
format is a wide-character string composed of zero or more
directives. Each directive is composed of one of the following: one or more
white-space wide characters ( <space>s, <tab>s, <newline>s,
<vertical-tab>s, or <form-feed>s); an ordinary wide character
(neither
'%' nor a white-space character); or a conversion
specification. Each conversion specification is introduced by a
'%'
or the sequence
"%n$" after which the
following appear in sequence:
- *
- An optional assignment-suppressing character '*'
.
- *
- An optional non-zero decimal integer that specifies the
maximum field width.
- *
- An optional length modifier that specifies the size of the
receiving object.
- *
- A conversion specifier wide character that specifies the
type of conversion to be applied. The valid conversion specifiers are
described below.
The
fwscanf() functions shall execute each directive of the format in
turn. If a directive fails, as detailed below, the function shall return.
Failures are described as input failures (due to the unavailability of input
bytes) or matching failures (due to inappropriate input).
A directive composed of one or more white-space wide characters is executed by
reading input until no more valid input can be read, or up to the first wide
character which is not a white-space wide character, which remains unread.
A directive that is an ordinary wide character shall be executed as follows. The
next wide character is read from the input and compared with the wide
character that comprises the directive; if the comparison shows that they are
not equivalent, the directive shall fail, and the differing and subsequent
wide characters remain unread. Similarly, if end-of-file, an encoding error,
or a read error prevents a wide character from being read, the directive shall
fail.
A directive that is a conversion specification defines a set of matching input
sequences, as described below for each conversion wide character. A conversion
specification is executed in the following steps.
Input white-space wide characters (as specified by
iswspace() ) shall be
skipped, unless the conversion specification includes a
[ ,
c ,
or
n conversion specifier.
An item shall be read from the input, unless the conversion specification
includes an
n conversion specifier wide character. An input item is
defined as the longest sequence of input wide characters, not exceeding any
specified field width, which is an initial subsequence of a matching sequence.
The first wide character, if any, after the input item shall remain unread. If
the length of the input item is zero, the execution of the conversion
specification shall fail; this condition is a matching failure, unless
end-of-file, an encoding error, or a read error prevented input from the
stream, in which case it is an input failure.
Except in the case of a
% conversion specifier, the input item (or, in
the case of a
%n conversion specification, the count of input wide
characters) shall be converted to a type appropriate to the conversion wide
character. If the input item is not a matching sequence, the execution of the
conversion specification shall fail; this condition is a matching failure.
Unless assignment suppression was indicated by a
'*' , the result of
the conversion shall be placed in the object pointed to by the first argument
following the
format argument that has not already received a
conversion result if the conversion specification is introduced by
% ,
or in the
nth argument if introduced by the wide-character
sequence
"%n$". If this object does not have an
appropriate type, or if the result of the conversion cannot be represented in
the space provided, the behavior is undefined.
The length modifiers and their meanings are:
- hh
- Specifies that a following d , i , o ,
u , x , X , or n conversion specifier applies
to an argument with type pointer to signed char or
unsigned char.
- h
- Specifies that a following d , i , o ,
u , x , X , or n conversion specifier applies
to an argument with type pointer to short or unsigned
short.
- l (ell)
- Specifies that a following d , i , o ,
u , x , X , or n conversion specifier applies
to an argument with type pointer to long or unsigned long;
that a following a , A , e , E , f ,
F , g , or G conversion specifier applies to an
argument with type pointer to double; or that a following c
, s , or [ conversion specifier applies to an argument with
type pointer to wchar_t.
- ll (ell-ell)
-
Specifies that a following d , i , o , u ,
x , X , or n conversion specifier applies to an
argument with type pointer to long long or unsigned long
long.
- j
- Specifies that a following d , i , o ,
u , x , X , or n conversion specifier applies
to an argument with type pointer to intmax_t or
uintmax_t.
- z
- Specifies that a following d , i , o ,
u , x , X , or n conversion specifier applies
to an argument with type pointer to size_t or the corresponding
signed integer type.
- t
- Specifies that a following d , i , o ,
u , x , X , or n conversion specifier applies
to an argument with type pointer to ptrdiff_t or the corresponding
unsigned type.
- L
- Specifies that a following a , A , e ,
E , f , F , g , or G conversion
specifier applies to an argument with type pointer to long double.
If a length modifier appears with any conversion specifier other than as
specified above, the behavior is undefined.
The following conversion specifier wide characters are valid:
- d
- Matches an optionally signed decimal integer, whose format
is the same as expected for the subject sequence of wcstol() with
the value 10 for the base argument. In the absence of a size
modifier, the application shall ensure that the corresponding argument is
a pointer to int.
- i
- Matches an optionally signed integer, whose format is the
same as expected for the subject sequence of wcstol() with 0 for
the base argument. In the absence of a size modifier, the
application shall ensure that the corresponding argument is a pointer to
int.
- o
- Matches an optionally signed octal integer, whose format is
the same as expected for the subject sequence of wcstoul() with the
value 8 for the base argument. In the absence of a size modifier,
the application shall ensure that the corresponding argument is a pointer
to unsigned.
- u
- Matches an optionally signed decimal integer, whose format
is the same as expected for the subject sequence of wcstoul() with
the value 10 for the base argument. In the absence of a size
modifier, the application shall ensure that the corresponding argument is
a pointer to unsigned.
- x
- Matches an optionally signed hexadecimal integer, whose
format is the same as expected for the subject sequence of
wcstoul() with the value 16 for the base argument. In the
absence of a size modifier, the application shall ensure that the
corresponding argument is a pointer to unsigned.
- a, e, f, g
-
Matches an optionally signed floating-point number, infinity, or NaN whose
format is the same as expected for the subject sequence of
wcstod(). In the absence of a size modifier, the application shall
ensure that the corresponding argument is a pointer to float.
If the
fwprintf() family of functions generates character string
representations for infinity and NaN (a symbolic entity encoded in
floating-point format) to support IEEE Std 754-1985, the
fwscanf() family of functions shall recognize them as input.
- s
- Matches a sequence of non white-space wide characters. If
no l (ell) qualifier is present, characters from the input field
shall be converted as if by repeated calls to the wcrtomb()
function, with the conversion state described by an mbstate_t
object initialized to zero before the first wide character is converted.
The application shall ensure that the corresponding argument is a pointer
to a character array large enough to accept the sequence and the
terminating null character, which shall be added automatically.
Otherwise, the application shall ensure that the corresponding argument is a
pointer to an array of
wchar_t large enough to accept the sequence and
the terminating null wide character, which shall be added automatically.
- [
- Matches a non-empty sequence of wide characters from a set
of expected wide characters (the scanset). If no l (ell)
qualifier is present, wide characters from the input field shall be
converted as if by repeated calls to the wcrtomb() function, with
the conversion state described by an mbstate_t object initialized
to zero before the first wide character is converted. The application
shall ensure that the corresponding argument is a pointer to a character
array large enough to accept the sequence and the terminating null
character, which shall be added automatically.
If an
l (ell) qualifier is present, the application shall ensure that the
corresponding argument is a pointer to an array of
wchar_t large enough
to accept the sequence and the terminating null wide character, which shall be
added automatically.
The conversion specification includes all subsequent wide characters in the
format string up to and including the matching right square bracket (
']' ). The wide characters between the square brackets (the
scanlist) comprise the scanset, unless the wide character after the
left square bracket is a circumflex (
'^' ), in which case the scanset
contains all wide characters that do not appear in the scanlist between the
circumflex and the right square bracket. If the conversion specification
begins with
"[]" or
"[^]" , the right square
bracket is included in the scanlist and the next right square bracket is the
matching right square bracket that ends the conversion specification;
otherwise, the first right square bracket is the one that ends the conversion
specification. If a
'-' is in the scanlist and is not the first wide
character, nor the second where the first wide character is a
'^' , nor
the last wide character, the behavior is implementation-defined.
- c
- Matches a sequence of wide characters of exactly the number
specified by the field width (1 if no field width is present in the
conversion specification).
If no
l (ell) length modifier is present, characters from the input field
shall be converted as if by repeated calls to the
wcrtomb() function,
with the conversion state described by an
mbstate_t object initialized
to zero before the first wide character is converted. The corresponding
argument shall be a pointer to the initial element of a character array large
enough to accept the sequence. No null character is added.
If an
l (ell) length modifier is present, the corresponding argument
shall be a pointer to the initial element of an array of
wchar_t large
enough to accept the sequence. No null wide character is added.
Otherwise, the application shall ensure that the corresponding argument is a
pointer to an array of
wchar_t large enough to accept the sequence. No
null wide character is added.
- p
- Matches an implementation-defined set of sequences, which
shall be the same as the set of sequences that is produced by the
%p conversion specification of the corresponding fwprintf()
functions. The application shall ensure that the corresponding argument is
a pointer to a pointer to void. The interpretation of the input
item is implementation-defined. If the input item is a value converted
earlier during the same program execution, the pointer that results shall
compare equal to that value; otherwise, the behavior of the %p
conversion is undefined.
- n
- No input is consumed. The application shall ensure that the
corresponding argument is a pointer to the integer into which is to be
written the number of wide characters read from the input so far by this
call to the fwscanf() functions. Execution of a %n
conversion specification shall not increment the assignment count returned
at the completion of execution of the function. No argument shall be
converted, but one shall be consumed. If the conversion specification
includes an assignment-suppressing wide character or a field width, the
behavior is undefined.
- C
- Equivalent to lc .
- S
- Equivalent to ls .
- %
- Matches a single '%' wide character; no conversion
or assignment shall occur. The complete conversion specification shall be
%% .
If a conversion specification is invalid, the behavior is undefined.
The conversion specifiers
A ,
E ,
F ,
G , and
X are also valid and shall be equivalent to, respectively,
a ,
e ,
f ,
g , and
x .
If end-of-file is encountered during input, conversion is terminated. If
end-of-file occurs before any wide characters matching the current conversion
specification (except for
%n ) have been read (other than leading
white-space, where permitted), execution of the current conversion
specification shall terminate with an input failure. Otherwise, unless
execution of the current conversion specification is terminated with a
matching failure, execution of the following conversion specification (if any)
shall be terminated with an input failure.
Reaching the end of the string in
swscanf() shall be equivalent to
encountering end-of-file for
fwscanf().
If conversion terminates on a conflicting input, the offending input shall be
left unread in the input. Any trailing white space (including <newline>)
shall be left unread unless matched by a conversion specification. The success
of literal matches and suppressed assignments is only directly determinable
via the
%n conversion specification.
The
fwscanf() and
wscanf() functions may mark the
st_atime
field of the file associated with
stream for update. The
st_atime field shall be marked for update by the first successful
execution of
fgetc(),
fgetwc(),
fgets(),
fgetws(),
fread(),
getc(),
getwc(),
getchar(),
getwchar(),
gets(),
fscanf(), or
fwscanf() using
stream that returns data not supplied by a prior call to
ungetc().
Upon successful completion, these functions shall return the number of
successfully matched and assigned input items; this number can be zero in the
event of an early matching failure. If the input ends before the first
matching failure or conversion, EOF shall be returned. If a read error occurs,
the error indicator for the stream is set, EOF shall be returned, and
errno shall be set to indicate the error.
For the conditions under which the
fwscanf() functions shall fail and may
fail, refer to
fgetwc() .
In addition,
fwscanf() may fail if:
- EILSEQ
- Input byte sequence does not form a valid character.
- EINVAL
- There are insufficient arguments.
The following sections are informative.
The call:
int i, n; float x; char name[50];
n = wscanf(L"%d%f%s", &i, &x, name);
with the input line:
assigns to
n the value 3, to
i the value 25, to
x the value
5.432, and
name contains the string
"Hamster" .
The call:
int i; float x; char name[50];
(void) wscanf(L"%2d%f%*d %[0123456789]", &i, &x, name);
with input:
assigns 56 to
i, 789.0 to
x, skips 0123, and places the string
"56\0" in
name. The next call to
getchar()
shall return the character
'a' .
In format strings containing the
'%' form of conversion specifications,
each argument in the argument list is used exactly once.
None.
None.
getwc() ,
fwprintf() ,
setlocale() ,
wcstod() ,
wcstol() ,
wcstoul() ,
wcrtomb() , the Base Definitions
volume of IEEE Std 1003.1-2001, Chapter 7, Locale,
<langinfo.h>,
<stdio.h>,
<wchar.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.opengroup.org/unix/online.html
.
