<TITLE>scanf</TITLE>
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<h3>SCANF(3) Linux Programmer's Manual SCANF(3)
</h3>
<h3>NAME
</h3> scanf, fscanf, sscanf, vscanf, vsscanf, vfscanf - input
format conversion
<h3>SYNOPSIS
</h3> #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);
<h3>DESCRIPTION
</h3> The scanf family of functions scans input according to a
format as described below. This format may contain con-
version specifiers; the results from such conversions, if
any, are stored through the pointer arguments. The scanf
function 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
argument 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
respectively.
Each successive pointer argument must correspond properly
with each successive conversion specifier (but see `sup-
pression' below). All conversions are introduced by the %
(percent sign) character. The format string may also con-
tain 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. Scan-
ning also stops when an input conversion cannot be made
(see below).
<h3>CONVERSIONS
</h3> 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.
h Indicates that the conversion will be one of dioux
<h3>BSD MANPAGE 29 November 1993 1
</h3>
<h3>SCANF(3) Linux Programmer's Manual SCANF(3)
</h3>
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).
L Indicates that the conversion will be efg and the
next pointer is a pointer to long double. (This
type is not implemented; the L flag is currently
ignored--this may not be true for Linux.)
In addition to these flags, there may be an optional maxi-
mum 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); other-
wise at most this many characters are scanned in process-
ing the conversion. Before conversion begins, most con-
versions 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
compatibility.
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 other-
wise. Only characters that correspond to the base
are used.
o Matches an octal integer; the next pointer must be
a pointer to unsigned int.
O Equivalent to lo; this exists for backwards compat-
ibility.
u Matches an optionally signed decimal integer; the
next pointer must be a pointer to unsigned int.
x Matches an optionally a signed hexadecimal integer;
the next pointer must be a pointer to unsigned int.
<h3>BSD MANPAGE 29 November 1993 2
</h3>
<h3>SCANF(3) Linux Programmer's Manual SCANF(3)
</h3>
X Equivalent to lx; this violates the ANSI
C3.159-1989 (``ANSI C'') but is backwards compati-
ble with previous UNIX systems--I don't know what
Linux does with this.
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 lf; this violates the ANSI
C3.159-1989 (``ANSI C'') but is backwards compati-
ble with previous UNIX systems--I don't know what
Linux does with this.
F Equivalent to lf; this exists only for backwards
compatibility.
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 terminating 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 special; 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
<h3>BSD MANPAGE 29 November 1993 3
</h3>
<h3>SCANF(3) Linux Programmer's Manual SCANF(3)
</h3>
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 charac-
ters 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.
For backwards compatibility, other conversion characters
(except `\0') are taken as if they were `%d' or, if upper-
case, `%ld', and a `conversion' of `%\0' causes an immedi-
ate return of EOF. The F and X conversions will be
changed in the future to conform to the
ANSI C standard, after which they will act like and
respectively. The behavior of Linux on the non-standard
points is not known by this documenter.
<h3>RETURN VALUES
</h3> 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 num-
ber of conversions which were successfully completed is
returned.
</pre>
<hr>
<h3>SEE ALSO
</h3><p>
<a href=strtol.htm>strtol</a>,
<a href=strtoul.htm>strtoul</a>,
<a href=strtod.htm>strtod</a>,
<a href=getc.htm>getc</a>,
<a href=printf.htm>printf</a>,
<pre>
<h3>STANDARDS
</h3> The functions fscanf, scanf, and sscanf conform to ANSI
C3.159-1989 (``ANSI C'').
<h3>BUGS
</h3> Differences for Linux are not known at this time. The
following is for the BSD version:
The current situation with %F and %X conversions is unfor-
tunate.
All of the backwards compatibility formats will be removed
<h3>BSD MANPAGE 29 November 1993 4
</h3>
<h3>SCANF(3) Linux Programmer's Manual SCANF(3)
</h3>
in the future.
Numerical strings are truncated to 512 characters; for
example, %f and %d are implicitly %512f and %512d.
<h3>BSD MANPAGE 29 November 1993 5
</h3>
</pre>
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