scanf(3) BSD Library Functions Manual scanf(3)
NAME
fscanf, scanf, sscanf, vfscanf, vscanf, vsscanf -- input format conver-
sion
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <stdio.h>
int
fscanf(FILE *restrict stream, const char *restrict format, ...);
int
scanf(const char *restrict format, ...);
int
sscanf(const char *restrict s, const char *restrict format, ...);
#include <stdarg.h>
#include <stdio.h>
int
vfscanf(FILE *restrict stream, const char *restrict format, va_list arg);
int
vscanf(const char *restrict format, va_list arg);
int
vsscanf(const char *restrict s, const char *restrict format,
va_list arg);
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 s.
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, respec-
tively.
Each successive pointer argument must correspond properly with each suc-
cessive conversion specifier (but see the * conversion below). All con-
versions 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 char-
acter. Scanning also stops when an input conversion cannot be made (see
below).
Extended locale versions of these functions are documented in scanf_l(3).
See xlocale(3) for more information.
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 dioux or n and the
next pointer is a pointer to a char (rather than int).
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 (ell) Indicates that the conversion will be one of dioux or n and the
next pointer is a pointer to a long int (rather than int), that
the conversion will be one of a, e, f, or g and the next pointer
is a pointer to double (rather than float), or that the conver-
sion will be one of c, s or [ and the next pointer is a pointer
to an array of wchar_t (rather than char).
ll (ell ell)
Indicates that the conversion will be one of dioux or n and the
next pointer is a pointer to a long long int (rather than int).
L Indicates that the conversion will be one of a, e, f, or g and
the next pointer is a pointer to long double.
j Indicates that the conversion will be one of dioux or n and the
next pointer is a pointer to a intmax_t (rather than int).
t Indicates that the conversion will be one of dioux or n and the
next pointer is a pointer to a ptrdiff_t (rather than int).
z Indicates that the conversion will be one of dioux or n and the
next pointer is a pointer to a size_t (rather than int).
q (deprecated.) Indicates that the conversion will be one of
dioux or n and 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 bytes are scanned in processing the
conversion. In the case of the lc, ls and l[ conversions, the field
width specifies the maximum number of multibyte characters that will be
scanned. 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.
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 oth-
erwise. Only characters that correspond to the base are used.
o Matches an octal integer; the next pointer must be a pointer to
unsigned int.
u Matches an optionally signed decimal integer; the next pointer must
be a pointer to unsigned int.
x, X Matches an optionally signed hexadecimal integer; the next pointer
must be a pointer to unsigned int.
a, A, e, E, f, F, g, G
Matches a floating-point number in the style of strtod(3). The
next pointer must be a pointer to float (unless l or L is speci-
fied.)
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.
If an l qualifier is present, the next pointer must be a pointer to
wchar_t, into which the input will be placed after conversion by
mbrtowc(3).
S The same as ls.
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.
If an l qualifier is present, the next pointer must be a pointer to
wchar_t, into which the input will be placed after conversion by
mbrtowc(3).
C The same as lc.
[ 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 ] charac-
ter. 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 cir-
cumflex, in) set or when the field width runs out.
If an l qualifier is present, the next pointer must be a pointer to
wchar_t, into which the input will be placed after conversion by
mbrtowc(3).
p Matches a pointer value (as printed by `%p' in printf(3)); the next
pointer must be a pointer to void * (or other pointer type).
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 decimal point character is defined in the program's locale (category
LC_NUMERIC).
For backwards compatibility, a ``conversion'' of `%\0' causes an immedi-
ate return of EOF.
RETURN VALUES
These functions return the number of input items assigned. This can be
fewer than provided for, or even zero, in the event of a matching fail-
ure. Zero indicates that, although there was input available, no conver-
sions 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), mbrtowc(3), printf(3), scanf_l(3), strtod(3), strtol(3),
strtoul(3), wscanf(3)
STANDARDS
The functions fscanf(), scanf(), sscanf(), vfscanf(), vscanf(), and
vsscanf() conform to ISO/IEC 9899:1999 (``ISO C99'').
BUGS
Earlier implementations of fscanf treated %D, %E, %F, %O and %X as their
lowercase equivalents with an l modifier. In addition, fscanf treated an
unknown conversion character as %d or %D, depending on its case. This
functionality has been removed.
Numerical strings are truncated to 512 characters; for example, %f and %d
are implicitly %512f and %512d.
The %n$ modifiers for positional arguments are not implemented.
The fscanf family of functions do not correctly handle multibyte charac-
ters in the format argument.
BSD January 4, 2003 BSD
Mac OS X 10.8 - Generated Thu Aug 30 11:41:48 CDT 2012