wscanf(3) Library Functions Manual wscanf(3)
NAME
wscanf, fwscanf, swscanf - Converts formatted wide-character input
LIBRARY
Standard C Library (libc)
SYNOPSIS
#include <wchar.h> #include <stdio.h>
int wscanf(
const wchar_t *format
[,pointer]...);
int fwscanf(
FILE *stream,
const wchar_t *format,
[,pointer]...);
int swscanf(
const wchar_t *wstr,
const wchar_t *format,
[,pointer]...);
STANDARDS
Interfaces documented on this reference page conform to industry standards as follows:
fwscanf(), swscanf(), wscanf(): XSH5.0
Refer to the standards(5) reference page for more information about industry standards and associated tags.
PARAMETERS
Specifies the format conversion. Specifies the input stream. Specifies a wide-character string to be read. Points to the location to
store the interpreted data.
DESCRIPTION
The wscanf(), fwscanf(), and swscanf() functions read wide-character data, interpret it according to a format, and store the converted
results into specified memory locations. The format parameter contains conversion specifications used to interpret the input. The pointer
parameters specify where to store the interpreted data.
These functions read their input from the following sources: Reads from standard input (stdin). Reads from the stream parameter. Reads
from the wide-character string specified by the wstr parameter.
If there are insufficient arguments for format, the function's behavior is undefined. If format is exhausted while arguments remain, the
excess arguments are evaluated as always but are otherwise ignored.
The format parameter can contain the following items: A conversion specification that directs the conversion of the next input field. Con-
version specifications start with a % (percent sign). Any white-space wide character (as determined by the iswspace() function) that
matches 0 (zero) or more white-space wide characters in the input stream. Any wide character except % (percent sign) or a white-space wide
character that must match the next wide character in the input stream.
The input stream is broken into fields based on the following: White space
All conversion specifications except %c, %C, and %[scanset] ignore leading white space and consider the first trailing white-space
wide character to delimit the field. Invalid wide character
If the input stream contains a wide character that is not allowed, this invalid wide character delimits the field and is considered
the first wide character of the next field. Maximum width
If the conversion specification includes a maximum width and the field is not terminated by white space or an invalid wide charac-
ter, then when that character position is reached in the input stream, the field is terminated.
Conversion Specifications
Each conversion specification in the format parameter has the following syntax: The character % (percent sign).
The wscanf(), fwscanf(), and swscanf() functions can also handle a format string that enables the system to process elements of the
pointer list in variable order. In such a case, the normal conversion character % (percent sign) is replaced by %digit$, where digit
is a decimal number in the range from 1 to NL_ARGMAX. Conversion is then applied to the specified pointer, rather than to the next
unused pointer. This feature provides for the definition of format strings in an order appropriate to specific languages. If the
variable ordering feature is used, it must be specified for all conversions except for conversion specifications that do not have
corresponding pointers (conversion specifications with the * (asterisk) assignment suppression and %% conversion specifications).
If more than one conversion specification specifies the same digit, the results of the function are undefined. The optional assign-
ment suppression character * (asterisk). An optional decimal digit string that specifies the maximum field width. An optional h or
l indicating the size of the receiving variable for some conversion specifiers, as follows: An h followed by a d, an i, or an n con-
version specifier indicates that the receiving variable is treated as unsigned short int; whereas an h followed by an o, a u, or an
x conversion specifier indicates that the receiving variable is treated as short int. An l followed by a d, an i, or an n conver-
sion specifier indicates that the receiving variable is treated as long int; whereas an l followed by an o, a u, or an x conversion
specifier indicates that the receiving variable is treated as unsigned long int. An l followed by a e, f, or g indicates that the
receiving variable is treated as double instead of float. An l followed by a c, an s, or a [scanset] conversion specifier indicates
that the receiving variable is treated as wchar_t instead of char. A conversion code character that specifies the type of conver-
sion to be applied: Accepts a single % (percent sign) input at this point; no assignment is done. The complete conversion specifica-
tion is %%. Accepts a decimal integer whose format is the same as expected for the subject sequence of the wcstol() function with
the value 10 for the base argument; the pointer parameter should be an integer pointer. Accepts a decimal integer whose format is
the same as expected for the subject sequence of the wcstol() function with the value 0 for the base argument; the pointer parameter
should be an integer pointer. Accepts an unsigned or signed decimal integer; the pointer parameter should be an unsigned integer
pointer. Accepts an octal integer; in the absence of a size modifier, the pointer parameter must be an unsigned integer pointer.
Accepts a hexadecimal integer; in the absence of a size modifier, the pointer parameter must be an unsigned integer pointer.
Accepts a floating-point number. The next field is converted accordingly and stored through the corresponding parameter, which
should be a pointer to a float. The input format for floating-point numbers is a string of digits, with the following optional char-
acteristics: It can be a signed value. It can be an exponential value, containing a decimal point followed by an exponent field,
which consists of an E or an e followed by an optionally signed integer. It can be one of the special values INF, NaNQ, or NaNS.
This value is translated into the ANSI/IEEE value for infinity, quiet NaN, or signaling NaN, respectively. Matches an unsigned
hexadecimal long integer, the same as the %p conversion of the wprintf() function. The corresponding argument will be a pointer to
void. No input is consumed. The corresponding argument is a pointer to an integer into which is written the number of wide charac-
ters read from the input stream so far by this function. The assignment count returned at the completion of this function is not
incremented. Accepts a string of nonwhite-space wide characters. The pointer parameter should be a pointer that points to an array
of wide characters large enough to accept the wide-character string with a terminating null wide character appended. The input
field ends with a white-space wide character. A string of wchar_t values is output. If a field width is given, pointer refers to a
wide-character array, and the indicated number of wchar_t values is read. Accepts a string of wide characters. The pointer parame-
ter should be a pointer to an array of wchar_t. The array must be large enough to accept the wide-character string with a terminat-
ing null wide character appended. The input field ends with a white-space wide character. A string of wchar_t is output. If the S
conversion specifier has a field width, the behavior of the conversion is undefined. Accepts a series of wide characters of the
number specified by the field width (1 if the directive contains no field width).
If the l qualifier is present, the corresponding argument must be a pointer to the initial element of a character array that is
large enough to accept the sequence. A null wide character is not added to the array. If the l qualifier is not present, the func-
tion converts input wide characters 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. A null byte is not added to the array. Because
the normal skip over white space is suppressed, use %1s rather than %1c to read the next nonwhite-space wide character. Accepts as
input one or more characters in multibyte format and converts to wchar_t type (as is done by the mbstowcs() or mbsrtowcs() func-
tion). If there is no field width or a field width of 1 in the conversion specification, the conversion result is one wide charac-
ter and the pointer parameter should be a wchar_t pointer. If the field width is greater than 1, the conversion result contains no
more than the indicated number of wide characters and the pointer parameter should be a wchar_t array. This array must be large
enough to accept the conversion result, which does not include a terminating null wide character. Because the normal skip over
white space is suppressed, use %1S rather than %1C to read the next nonwhite-space character. Accepts as input the wide characters
included in the scanset. The scanset parameter explicitly defines the wide characters that are accepted in the string data as those
enclosed within [ ] (square brackets). The corresponding pointer parameter should be an array of wchar_t. The leading white space
that is normally skipped over is suppressed. A scanset in the form of [^scanset] is an exclusive scanset: the ^ (circumflex) serves
as a complement operator and the following characters in the scanset are not accepted as input. Conventions used in the construction
of the scanset follow: You can represent a range of characters by the construct first-last. Thus, you can express [0123456789] as
[0-9]. The first parameter must be lexically less than or equal to the last parameter, or else the - (dash) stands for itself. The -
also stands for itself whenever it is the first or the last character in the scanset. You can include the ] (right bracket) as an
element of the scanset if it is the first character of the scanset. In this case, it is not interpreted as the bracket that closes
the scanset. If the scanset is an exclusive scanset, the ] is preceded by the ^ (circumflex) to make the ] an element of the
scanset. The corresponding pointer parameter must point to a wide-character array large enough to hold the data field and that ends
with a null wide character. The terminating null is added automatically.
The conversion specification syntax is summarized by the following synopsis:
%[digit$][*][width][sizecode]convcode
The results from the conversion are placed in *pointer unless you specify assignment suppression with an * (asterisk). Assignment suppres-
sion provides a way to describe an input field that is to be skipped. The input field is a string of nonwhite-space characters. It extends
to the next inappropriate wide character or until the field width, if specified, is exhausted.
The conversion code indicates how to interpret the input field. The corresponding pointer must usually be of a restricted type. You should
not specify the pointer parameter for a suppressed field.
A wscanf() function ends at the end of the file, the end of the control string, or when an input wide character conflicts with the control
string. If wscanf() ends with an input wide character conflict, the conflicting wide character is not read from the input stream.
Unless there is a match in the control string, trailing white space (including a newline wide character) is not read.
The success of literal matches and suppressed assignments cannot be directly determined. The wscanf() function returns the number of suc-
cessfully matched and assigned input items.
RESTRICTIONS
Currently, the operating system does not provide any locales that use shift-state encoding. Therefore, restartable conversion functions
(such mbsrtowcs()) that use the mbstate_t object do not differ from their nonrestartable counterparts. Information related to shift-state
encoding is included in this reference page for your convenience in porting applications to other platforms, some of which may provide
locales with shift-state encoding.
RETURN VALUES
The wscanf(), fwscanf(), or swscanf() function returns the number of successfully matched and assigned input items. This number can be 0
(zero) if there was an early conflict between an input wide character and the control string. If the input ends before the first conflict
or conversion, the function returns EOF (End-of-File).
ERRORS
The fwscanf() function fails if either the stream is unbuffered, or the stream's buffer needed to be flushed and the function call caused
an underlying read() or lseek() to be invoked and that operation fails. In addition, if the any of the following conditions occur, the
wscanf(), fwscanf(), and swscanf(), functions set errno to the corresponding value: The O_NONBLOCK flag is set for the underlying stream
and the process would be delayed by the read operation. The file descriptor underlying the stream is not a valid file descriptor or is not
open for reading. The input byte sequence does not form a valid wide character. The read operation was interrupted by a signal that was
caught and no data was transferred. A physical I/O error occurred, or the process is in a background process group attempting to read from
its controlling terminal, and either the process is ignoring or blocking the SIGTTIN signal or the process group is orphaned. Insufficient
memory is available for the operation.
RELATED INFORMATION
Functions: fopen(3), getwc(3), printf(3), scanf(3), wprintf(3)
Standards: standards(5) delim off
wscanf(3)