fwscanf(3C) fwscanf(3C)
NAME
fwscanf(), wscanf(), swscanf() - convert formatted wide-character
input
SYNOPSIS
#include <<<<stdio.h>>>>
#include <<<<wchar.h>>>>
int fwscanf(FILE *stream, const wchar_t *format, ... );
int wscanf(const wchar_t *format, ... );
int swscanf(const wchar_t *s, const wchar_t *format, ... );
DESCRIPTION
The fwscanf() function reads from the named input stream.
The wscanf() function reads from the standard input stream stdin. The
swscanf() reads from the wide-character string s.
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 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.
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 defaults
to a period (.).
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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, tab, newline,
vertical-tab or form-feed characters);
+ 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 size modifier h, l (ell) or L indicating the size
of the receiving object.
The conversion wide-characters c, s and [ must be precede by l
(ell) if the corresponding argument is a pointer to wchar_t
rather than a pointer to a character type.
The conversion wide-characters d, i and n must be preceded by
h if the corresponding argument is a pointer to short int
rather than a pointer to int, or by l (ell) if it is a pointer
to long int.
Similarly, the conversion wide-characters o, u and x must be
preceded by h if the corresponding argument is a pointer to
unsigned short int rather than a pointer to unsigned int or by
l (ell) if it is a pointer to unsigned long int.
The conversion wide-characters e, f and g must be preceded by
l (ell) if the corresponding argument is a pointer to double
rather than a pointer to float, or by L if it is a pointer to
long double. If an h, l (ell) or L appears with any other
conversion wide-character, the behavior is undefined.
+ A conversion wide-character that specifies the type of
conversion to be applied. The valid conversion wide-
characters are described below.
The fwscanf() functions execute each directive of the format in turn.
If a directive fails, as detailed below, the function returns.
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
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to the first wide-character which is not a white-space wide-character,
which remains unread.
A directive that is an ordinary wide-character is 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 fails, and the differing
and subsequent wide-characters remain unread.
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()) are
skipped, unless the conversion specification includes a [, c or n
conversion character.
An item is read from the input, unless the conversion specification
includes an n conversion 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
remains unread. If the length of the input item is 0, the execution
of the conversion specification fails; 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 wide-character, the input item
(or, in the case of a %n conversion specification, the count of input
wide-characters) is 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 fails; this condition is a
matching failure. Unless assignment suppression was indicated by a *,
the result of the conversion is 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 following conversion 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 corresponding
argument must be a pointer to int.
i Matches an optionally signed integer, whose format is
the same as expected for the subject sequence of
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wcstol() with 0 for the base argument. In the absence
of a size modifier, the corresponding argument must be
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 corresponding
argument must be a pointer to unsigned int.
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 corresponding
argument must be a pointer to unsigned int.
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 corresponding
argument must be a pointer to unsigned int.
e,f,g Matches an optionally signed floating-point number,
whose format is the same as expected for the subject
sequence of wcstod(). In the absence of a size
modifier, the corresponding argument must be a pointer
to float.
If the fwprintf() family of functions generates character string
representations for infinity and NaN (a 7858 symbolic entity encoded
in floating-point format) to support the ANSI/IEEE Std 754:1985
standard, the fwscanf() family of functions will 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 are 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 must be a pointer to a character
array large enough to accept the sequence and the
terminating null character, which will be added
automatically.
Otherwise, the corresponding argument must be a pointer to an array of
wchar_t large enough to accept the sequence and the terminating null
wide-character, which will be added automatically.
[ Matches a non-empty sequence of wide-characters from a
set of expected wide-characters (the scanset). If no l
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(ell) qualifier is present, wide-characters from the
input field are 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 must be a pointer to a character
array large enough to accept the sequence and the
terminating null character, which will be added
automatically.
If an l (ell) qualifier is present, the corresponding argument must be
a pointer to an array of wchar_t large enough to accept the sequence
and the terminating null wide-character, which will 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-dependent.
c Matches a sequence of wide-characters of the number
specified by the field width (1 if no field width is
present in the conversion specification). If no l
(ell) qualifier is present, wide-characters from the
input field are 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 must be a pointer to a character
array large enough to accept the sequence. No null
character is added. Otherwise, the corresponding
argument must be a pointer to an array of wchar_t large
enough to accept the sequence. No null wide-character
is added.
p Matches an implementation-dependent set of sequences,
which must be the same as the set of sequences that is
produced by the %p conversion of the corresponding
fwprintf() functions. The corresponding argument must
be a pointer to a pointer to void. If the input item
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is a value converted earlier during the same program
execution, the pointer that results will compare equal
to that value; otherwise the behavior of the %p
conversion is undefined.
n No input is consumed. The corresponding argument must
be 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 does not increment the
assignment count returned at the completion of
execution of the function.
C Same as lc.
S Same as ls.
% Matches a sigle %; no conversion or assignment occurs.
The complete conversion specification must be %%.
If a conversion specification is invalid, the behavior is undefined.
The conversion characters E, G and X are also valid and behave the
same as, respectively, e, 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 terminates 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) is terminated with an input failure.
Reaching the end of the string in swscanf() is equivalent to
encountering end-of-file for fwscanf().
If conversion terminates on a conflicting input, the offending input
is left unread in the input. Any trailing white space (including
newline) is 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 will
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().
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APPLICATION USAGE
fwscanf(), wscanf(), swscanf() are thread-safe interfaces. After
fwscanf() or wscanf() is applied to a stream, the stream becomes
wide-oriented (see orientation(5)).
In format strings containing the % form of conversion specifications,
each argument in the argument list is used exactly once.
RETURN VALUE
Upon successful completion, these functions return the number of
successfully matched and assigned input items; this number can be 0 in
the event of an early matching failure. If the input ends before the
first matching failure or conversion, EOF is returned. If a read
error occurs the error indicator for the stream is set, EOF is
returned, and errno is set to indicate the error.
ERRORS
For the conditions under which the fwscanf() functions will 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.
[ENOMEM] Insufficient storage space is available.
In addition, fwscanf() may fail if:
[EILSEQ] The stream pointed to by stream is byte-oriented.
In addition, wscanf() may fail if:
[EILSEQ] stdin is byte-oriented.
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
will assign to n the value 3, to i the value 25, x the value 5.432,
and name will contain the string Hamster.
The call:
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int i; float x; char name[50];
(void)wscanf(L"%2d%f%*d %[0123456789]", &&&&i, &&&&x, name);
with input:
56789 0123 56a72
will assign 56 to i, 789.0 to x, skip 0123, and place the string 56 in
name. The next call to getchar() will return the character a.
AUTHOR
fwscanf(), wscanf(), swscanf() were developed by HP and Mitsubishi
Electric Corporation.
SEE ALSO
getwc(3C), fwprintf(3C), setlocale(3C), wcstod(3C), wcstol(3C),
wcstoul(3C), wcrtomb(3C), langinfo(5), orientation(5).
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