NAME
scanf, fscanf,
sscanf, vscanf,
vsscanf, vfscanf —
input format 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 read input according to the given
format as described below. This format may contain
“conversion specifiers”; the results of such conversions, if
any, are stored through a set of pointer arguments.
The
scanf()
function reads input from the standard input stream
stdin,
fscanf()
reads input from the supplied 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
va_start(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
the * conversion below). All conversions are
introduced by the % (percent sign) character. The
format string may also contain other characters.
Whitespace (such as blanks, tabs, or newlines) in the
format string match any amount of whitespace,
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.
hh- Indicates that the conversion will be one of
diouxornand the next pointer is a pointer to a char (rather than int). h- Indicates that the conversion will be one of
diouxornand the next pointer is a pointer to a short int (rather than int). l(ell)- 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), or that the conversion will be one ofsc[.If the conversion is one of
sc[the expected conversion input is a multibyte character sequence. Each multibyte character in the sequence is converted with a call to thembrtowc() function. The field width specifies the maximum amount of bytes read from the multibyte character sequence and passed tombrtowc() for conversion. The next pointer is a pointer to a wchar_t wide-character buffer large enough to accept the converted input sequence including the terminating NUL wide character which will be added automatically. ll(ell ell)- Indicates that the conversion will be one of
diouxornand the next pointer is a pointer to a long long int (rather than int). L- Indicates that the conversion will be one of
efgand the next pointer is a pointer to long double. j- Indicates that the conversion will be one of
diouxornand the next pointer is a pointer to an intmax_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). q- (deprecated) Indicates that the conversion will be one of
diouxornand the next pointer is a pointer to a long long int (rather than int).
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 whitespace; this whitespace 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.
xX- Matches an optionally signed hexadecimal integer; the next pointer must be a pointer to unsigned int.
eE- Equivalent to
f. fF- Matches an optionally signed floating-point number; the next pointer must be a pointer to float.
gG- Equivalent to
f. aA- Equivalent to
f. s- Matches a sequence of non-whitespace characters; the next pointer must be a pointer to char, or to wchar_t if the l length modifier is present. The provided array must be large enough to accept and store the whole sequence and the terminating NUL character. The input string stops at whitespace or at the maximum field width, whichever occurs first. If specified, the maximum field length refers to the sequence being scanned rather than the storage space, hence the provided array must be 1 larger for the terminating NUL character.
c- Matches a sequence of characters consuming the number of bytes specified by the field width (defaults to 1 if unspecified); the next pointer must be a pointer to char, or to wchar_t if the l length modifier is present. There must be enough room for all the characters (no terminating NUL is added). The usual skip of leading whitespace is suppressed. To skip whitespace 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, or to wchar_t if the
l length modifier is present. There must be enough
room for all the characters in the string, plus a terminating NUL
character. The usual skip of leading whitespace 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 (or, with a circumflex, in) the 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.
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, such as an
end-of-file, occurs before any conversion. 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), mbrtowc(3), printf(3), strtod(3), strtol(3), strtoul(3), wscanf(3)
STANDARDS
The functions fscanf(),
scanf(), and sscanf()
conform to ANSI X3.159-1989
(“ANSI C89”).
HISTORY
The functions scanf(),
fscanf(), and sscanf() first
appeared in Version 7 AT&T UNIX, and
vscanf(), vsscanf(), and
vfscanf() in
4.3BSD-Reno.
CAVEATS
On systems other than OpenBSD, the
LC_NUMERIC
locale(1) category can cause parsing failures; see CAVEATS in
setlocale(3) for details.
BUGS
Numerical strings are truncated to 512 characters; for example,
%f and %d are implicitly
%512f and %512d.