NAME
scanf, fscanf,
sscanf, vscanf,
vsscanf, vfscanf —
input format conversion
LIBRARY
library “libc”
SYNOPSIS
#include
<stdio.h>
int
scanf(const
char * restrict format,
...);
int
fscanf(FILE
* restrict stream, const
char * restrict format,
...);
int
sscanf(const
char * restrict str,
const char * restrict
format, ...);
#include
<stdarg.h>
int
vscanf(const
char * restrict format,
va_list ap);
int
vsscanf(const
char * restrict str,
const char * restrict
format, va_list
ap);
int
vfscanf(FILE
* restrict stream, const
char * restrict format,
va_list ap);
DESCRIPTION
The
scanf()
family of functions scans input according to a format
as described below. This format may contain
conversion
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 `suppression'
below). All conversions are introduced by the %
(percent 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.
h- Indicates that the conversion will be one of
diouxornand the next pointer is a pointer to a short int (rather than int). hh- Indicates that the conversion will be one of
diouxornand the next pointer is a pointer to a char (rather than int). j- Indicates that the conversion will be one of
diouxornand the next pointer is a pointer to an intmax_t (rather than int). l- Indicates either that the conversion will be one of
diouxornand the next pointer is a pointer to a long int (rather than int), or that the conversion will be one ofefgand the next pointer is a pointer to double (rather than float). ll- Indicates that the conversion will be one of
diouxornand the next pointer is a pointer to a long long int (rather than int). q- Indicates that the conversion will be one of
diouxornand the next pointer is a pointer to a quad_t (rather than int). t- Indicates that the conversion will be one of
diouxornand the next pointer is a pointer to a ptrdiff_t (rather than int). z- Indicates that the conversion will be one of
diouxornand the next pointer is a pointer to a size_t (rather than int). L- Indicates that the conversion will be
efgand the next pointer is a pointer to long double.
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 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 otherwise. 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 compatibility. u- Matches an optionally signed decimal integer; the next pointer must be a pointer to unsigned int.
x- Matches an optionally signed 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. G- 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
NULcharacter. 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
NULis 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
NULcharacter. 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 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.
For backwards compatibility, other conversion characters (except
‘\0’) are taken as if they were
‘%d’ or, if uppercase,
‘%ld’, and a `conversion' of
‘%\0’ causes an immediate return of
EOF.
The format string specifier macros described in inttypes(3) should be used for the standard “C99” fixed-size integers documented in stdint(3).
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
getc(3), inttypes(3), printf(3), strtod(3), strtol(3), strtoul(3)
STANDARDS
The functions fscanf(),
scanf(), and sscanf()
conform to ISO/IEC 9899:1990
(“ISO C90”). The %j,
%t and %z conversion format
modifiers conform to ISO/IEC 9899:1999
(“ISO C99”). The
vfscanf(), vscanf() and
vsscanf() functions conform to
ISO/IEC 9899:1999
(“ISO C99”).
HISTORY
The functions vscanf(),
vsscanf() and vfscanf()
appeared in 4.4BSD or even
4.3BSD.
NOTES
All of the backwards compatibility formats will be removed in the future.
BUGS
Numerical strings are truncated to 512 characters; for example,
%f and %d are implicitly
%512f and %512d.