FSCANF(2) FSCANF(2)
NAME
fscanf, scanf, sscanf, vfscanf - scan formatted input
SYNOPSIS
#include <u.h>
#include <stdio.h>
int fscanf(FILE *f, char *format, ...)
int scanf(char *format, ... )
int sscanf(char *s, char *format, ...)
int vfscanf(FILE *stream, char *format, char *args)
DESCRIPTION
Fscanf reads from the named input stream f (see fopen(2))
under control of the string pointed to by format that speci-
fies the admissible input sequences and how they are to be
converted for assignment, using subsequent arguments as
pointers to the objects to receive the converted input. If
there are insufficient arguments for the format, the behav-
ior is undefined. If the format is exhausted while argu-
ments remain, the excess arguments are evaluated (as always)
but are otherwise ignored.
Scanf and sscanf are the same, but they read from stdin and
the character string s, respectively. Vfscanf is like
scanf, except the args argument is a pointer to an argument
in an argument list of the calling function and the effect
is as if the calling function's argument list from that
point on is passed to the scanf routines.
The format is composed of zero or more directives: one or
more white-space characters; an ordinary character (not %);
or a conversion specification. Each conversion specifica-
tion is introduced by the character %. After the %, the
following appear in sequence:
An optional assignment-suppressing character *.
An optional decimal integer that specifies the maximum
field width.
An optional h, l (ell) or L indicating the size of the
receiving object. The conversion specifiers d, i, and
n shall be preceded by h if the corresponding argument
is a pointer to short rather than a pointer to int, or
by l if it is a pointer to long. Similarly, the con-
version specifiers o, u, and x shall be preceded by h
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if the corresponding argument is a pointer to unsigned
short rather than a pointer to unsigned, or by l if it
is a pointer to unsigned long. Finally, the conversion
specifiers e, f, and g shall be preceded by l 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, or L appears with any other
conversion specifier, the behavior is undefined.
A character that specifies the type of conversion to be
applied. The valid conversion specifiers are described
below.
Fscanf executes each directive of the format in turn. If a
directive fails, as detailed below, fscanf returns. Fail-
ures are described as input failures (due to the unavail-
ability of input), or matching failures (due to inappropri-
ate input).
A directive composed of white space is executed by reading
input up to the first non-white-space character (which
remains unread), or until no more characters can be read.
A directive that is an ordinary character is executed by
reading the next character from the stream. If if differs
from the one comprising the directive, the directive fails,
and the differing and subsequent characters remain unread.
A directive that is a conversion specification defines a set
of matching input sequences, as described below for each
specifier. A conversion specification is executed in the
following steps:
Input white-space characters (as specified by isspace, see
ctype(2)) are skipped, unless the specification includes a
[, c, or n specifier.
An input item is read from the stream, unless the specifica-
tion includes an n specifier. An input item is defined as
the longest sequence of input characters (up to any speci-
fied maximum field width) which is an initial subsequence of
a matching sequence. The first character, if any, after the
input item remains unread. If the length of the input item
is zero, the execution of the directive fails: this condi-
tion is a matching failure, unless an error prevented input
from the stream, in which case it is an input failure.
Except in the case of a % specifier, the input item (or, in
the case of a %n directive, the count of input characters)
is converted to a type appropriate to the conversion speci-
fier. If the input item is not a matching sequence, the
execution of the directive fails: this condition is a
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FSCANF(2) FSCANF(2)
matching failure. Unless assignment suppression was indi-
cated 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 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 specifiers are valid:
d Matches an optionally signed decimal integer, whose
format is the same as expected for the subject
sequence of the strtol (see atof(2)) function with 10
for the base argument. The corresponding argument
shall be a pointer to int.
i Matches an optionally signed decimal integer, whose
format is the same as expected for the subject
sequence of the strtol function with 0 for the base
argument. The corresponding argument shall be a
pointer to int.
o Matches an optionally signed octal integer, whose for-
mat is the same as expected for the subject sequence
of the strtoul (see atof(2)) function with 8 for the
base argument. The corresponding argument shall 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 the strtoul function with 10 for the base
argument. The corresponding argument shall 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 the strtoul function with 16 for the base
argument. The corresponding argument shall 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
string of the strtod (see atof(2)) function. The cor-
responding argument shall be a pointer to float.
s Matches a sequence of non-white-space characters. The
corresponding argument shall be a pointer to the ini-
tial character of an array large enough to accept the
sequence and a terminating NUL (0) character, which
will be added automatically.
[ Matches a nonempty sequence of characters from a set
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of expected characters (the scanset). The correspond-
ing argument shall be a pointer to the initial charac-
ter of an array large enough to accept the sequence
and a terminating NUL character, which will be added
automatically. The conversion specifier includes all
subsequent characters in the format string, up to and
including the matching right brace (]). The charac-
ters between the brackets (the scanlist) comprise the
scanset, unless the character after the left bracket
is a circumflex (^), in which case the scanset con-
tains all characters that do not appear in the scan-
list between the circumflex and the right bracket. As
a special case, if the conversion specifier begins
with [] or [^], the right bracket character is in the
scanlist and the next right bracket character is the
matching right bracket that ends the specification.
If a - character is in the scanlist and is not the
first, nor the second where the first character is a
^, nor the last character, the behavior is
implementation-defined (in Plan 9: the scanlist
includes all characters in the ASCII (sic) range
between the two characters on either side of the -).
c Matches a sequence of characters of the number speci-
fied by the field width (1 if no field width is pre-
sent in the directive). The corresponding argument
shall be a pointer to the initial character of an
array large enough to accept the sequence. No NUL
character is added.
P Matches an implementation-defined set of sequences,
which should be the same as the set of sequences that
may be produced by the %P conversion of the fprintf(2)
function (in Plan 9, a hexadecimal number). The cor-
responding argument shall be a pointer to a pointer to
void. The interpretation of the input item is imple-
mentation defined; however, for any input item other
than a value converted earlier during the same program
execution, the behavior of the %P conversion is unde-
fined.
n No input is consumed. The corresponding argument
shall be a pointer to integer into which is written
the number of characters read from the input stream so
far by this call to fscanf. Execution of a %n direc-
tive does not increment the assignment count returned
at the completion of fscanf.
% Matches a single %; no conversion or assignment
occurs. The complete conversion specification shall
be %%.
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If a conversion specification is invalid, the behavior is
undefined.
The conversion specifiers 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 characters
matching the current directive have been read (other than
leading white space, where permitted), execution of the cur-
rent directive terminates with an input failure; otherwise,
unless execution of the current directive is terminated with
a matching failure, execution of the following directive (if
any) is terminated with an input failure.
If conversion terminates on a conflicting input character,
the offending input character is left unread in the input
stream. Trailing white space (including newline characters)
is left unread unless matched by a directive. The success
of literal matches and suppressed assignments is not
directly determinable other than via the %n directive.
The return value from fscanf is the number of input items
assigned, which can be fewer than provided for, or even
zero, in the event of an early matching failure. However,
if an input failure occurs before any conversion, EOF is
returned.
SOURCE
/sys/src/libstdio
SEE ALSO
fopen(2), fgetc(2)
BUGS
Does not know about UTF.
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