NAME
scanf, fscanf, sscanf, vscanf, vsscanf, vfscanf - input for-
mat conversion
SYNOPSIS
#include <stdio.h>
int scanf( const char *format, ...);
int fscanf( FILE *stream, const char *format, ...);
int sscanf( const char *str, const char *format, ...);
#include <stdarg.h>
int vscanf( const char *format, va_list ap));
int vsscanf( const char *str, const char *format, va_list ap
int vfscanf( FILE *stream, const char *format, va_list ap
DESCRIPTION
The scanf family of functions scans input according to a
format as described below. This format may contain conver-
sion specifiers; the results from such conversions, if any,
are stored through the pointer arguments. The scanf func-
tion reads input from the standard input stream stdin,
fscanf reads input from the stream pointer stream, and
sscanf reads its input from the character string pointed to
by str.
The vfscanf function is analogous to vfprintf(3) and reads
input from the stream pointer stream using a variable argu-
ment list of pointers (see stdarg(3). The vscanf function
scans a variable argument list from the standard input and
the vsscanf function scans it from a string; these are
analogous to the vprintf and vsprintf functions respec-
tively.
Each successive pointer argument must correspond properly
with each successive conversion specifier (but see `suppres-
sion' below). All conversions are introduced by the % (per-
cent sign) character. The format string may also contain
other characters. White space (such as blanks, tabs, or
newlines) in the format string match any amount of white
space, including none, in the input. Everything else
matches only itself. Scanning stops when an input character
does not match such a format character. Scanning also stops
when an input conversion cannot be made (see below).
CONVERSIONS
Following the % character introducing a conversion there may
be a number of flag characters, as follows:
* Suppresses assignment. The conversion that follows
occurs as usual, but no pointer is used; the result of
the conversion is simply discarded.
a Indicates that the conversion will be s, the needed
memory space for the string will be malloc'ed and the
pointer to it will be assigned to the char pointer
variable, which does not have to be initialised before.
This flag does not exist in ANSI C.
h Indicates that the conversion will be one of dioux or n
and the next pointer is a pointer to a short int
(rather than int).
l Indicates either that the conversion will be one of
dioux or n and the next pointer is a pointer to a long
int (rather than int), or that the conversion will be
one of efg and the next pointer is a pointer to double
(rather than float). Specifying two l flags is
equivalent to the L flag.
L Indicates that the conversion will be either efg and
the next pointer is a pointer to long double or the
conversion will be dioux and the next pointer is a
pointer to long long. (Note that long long is not an
ANSI C type. Any program using this will not be port-
able to all architectures).
q equivalent to L. This flag does not exist in ANSI C.
In addition to these flags, there may be an optional maximum
field width, expressed as a decimal integer, between the %
and the conversion. If no width is given, a default of
`infinity' is used (with one exception, below); otherwise at
most this many characters are scanned in processing the
conversion. Before conversion begins, most conversions skip
white space; this white space is not counted against the
field width.
The following conversions are available:
% Matches a literal `%'. That is, `%%' in the format
string matches a single input `%' character. No
conversion is done, and assignment does not occur.
d Matches an optionally signed decimal integer; the next
pointer must be a pointer to int.
D Equivalent to ld; this exists only for backwards compa-
tibility. (Note: thus only in libc4. In libc5 and
glibc the %D is silently ignored, causing old programs
to fail mysteriously.)
i Matches an optionally signed integer; the next pointer
must be a pointer to int. The integer is read in base
16 if it begins with `0x' or `0X', in base 8 if it
begins with `0', and in base 10 otherwise. Only char-
acters that correspond to the base are used.
o Matches an unsigned octal integer; the next pointer
must be a pointer to unsigned int.
u Matches an unsigned decimal integer; the next pointer
must be a pointer to unsigned int.
x Matches an unsigned hexadecimal integer; the next
pointer must be a pointer to unsigned int.
X Equivalent to x
f Matches an optionally signed floating-point number; the
next pointer must be a pointer to float.
e Equivalent to f.
g Equivalent to f.
E Equivalent to f
s Matches a sequence of non-white-space characters; the
next pointer must be a pointer to char, and the array
must be large enough to accept all the sequence and the
terminating NUL character. The input string stops at
white space or at the maximum field width, whichever
occurs first.
c Matches a sequence of width count characters (default
1); the next pointer must be a pointer to char, and
there must be enough room for all the characters (no
terminating NUL is added). The usual skip of leading
white space is suppressed. To skip white space first,
use an explicit space in the format.
[ Matches a nonempty sequence of characters from the
specified set of accepted characters; the next pointer
must be a pointer to char, and there must be enough
room for all the characters in the string, plus a ter-
minating NUL character. The usual skip of leading
white space is suppressed. The string is to be made up
of characters in (or not in) a particular set; the set
is defined by the characters between the open bracket [
character and a close bracket ] character. The set
excludes those characters if the first character after
the open bracket is a circumflex ^. To include a close
bracket in the set, make it the first character after
the open bracket or the circumflex; any other position
will end the set. The hyphen character - is also spe-
cial; when placed between two other characters, it adds
all intervening characters to the set. To include a
hyphen, make it the last character before the final
close bracket. For instance, `[^]0-9-]' means the set
`everything except close bracket, zero through nine,
and hyphen'. The string ends with the appearance of a
character not in the (or, with a circumflex, in) set or
when the field width runs out.
p Matches a pointer value (as printed by `%p' in
printf(3); the next pointer must be a pointer to void.
n Nothing is expected; instead, the number of characters
consumed thus far from the input is stored through the
next pointer, which must be a pointer to int. This is
not a conversion, although it can be suppressed with
the * flag. The C standard says: `Execution of a %n
directive does not increment the assignment count
returned at the completion of execution' but the Corri-
gendum seems to contradict this. Probably it is wise
not to make any assumptions on the effect of %n conver-
sions on the return value.
RETURN VALUES
These functions return the number of input items assigned,
which can be fewer than provided for, or even zero, in the
event of a matching failure. Zero indicates that, while
there was input available, no conversions were assigned;
typically this is due to an invalid input character, such as
an alphabetic character for a `%d' conversion. The value
EOF is returned if an input failure occurs before any
conversion such as an end-of-file occurs. If an error or
end-of-file occurs after conversion has begun, the number of
conversions which were successfully completed is returned.
SEE ALSO
strtol(3), strtoul(3), strtod(3),
STANDARDS
The functions fscanf, scanf, and sscanf conform to ANSI
C3.159-1989 (``ANSI C'').
The q flag is the BSD 4.4 notation for long long, while ll
or the usage of L in integer conversions is the GNU nota-
tion.
The Linux version of these functions is based on the GNU
libio library. Take a look at the info documentation of GNU
libc (glibc-1.08) for a more concise description.
BUGS
All functions are fully ANSI C3.159-1989 conformant, but
provide the additional flags q and a as well as an addi-
tional behaviour of the L and l flags. The latter may be
considered to be a bug, as it changes the behaviour of flags
defined in ANSI C3.159-1989.
Some combinations of flags defined by ANSI C are not making
sense in ANSI C (e.g. %Ld). While they may have a well-
defined behaviour on Linux, this need not to be so on other
architectures. Therefore it usually is better to use flags
that are not defined by ANSI C at all, i.e. use q instead of
L in combination with diouxX conversions or ll.
The usage of q is not the same as on BSD 4.4, as it may be
used in float conversions equivalently to L.