SCANF(3) BSD Library Functions Manual SCANF(3)
NAME
fscanf, scanf, sscanf, vfscanf, vscanf, vsscanf -- input format conversion
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, 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. 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).
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 fol-lows: follows:
lows:
* 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 conversion 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 inte-ger, integer,
ger, 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 `%' charac-ter. character.
ter. 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
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.
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 specified.)
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 ] 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.
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.
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 immediate 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 failure. Zero indicates that, although there was input avail-able, available,
able, 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 conver-sion conversion
sion 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 characters in the format argument.
BSD January 4, 2003 BSD
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