NAME
fwscanf, swscanf, wscanf - convert formatted wide-character input
SYNOPSIS
#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, ... );
DESCRIPTION
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().
RETURN VALUE
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.
ERRORS
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.
EXAMPLES
The call:
int i, n; float x; char name[50];
n = wscanf(L"%d%f%s", &i, &x, name);
with the input line:
25 54.32E-1 Hamster
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:
56789 0123 56a72
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’ .
APPLICATION USAGE
In format strings containing the ’%’ form of conversion specifications,
each argument in the argument list is used exactly once.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
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>
COPYRIGHT
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 .