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 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 that the conversion will be one of
diouxornand the next pointer is a pointer to a long int (rather than int), that the conversion will be one ofa,e,f, organd the next pointer is a pointer to double (rather than float), or that the conversion will be one ofc,sor[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
diouxornand 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, organd 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 a 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 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 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
lorLis 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
NULcharacter. The input string stops at white space or at the maximum field width, whichever occurs first.If an
lqualifier 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
NULis added). The usual skip of leading white space is suppressed. To skip white space first, use an explicit space in the format.If an
lqualifier 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
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.If an
lqualifier 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 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 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), 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.