NAME
scanf,
fscanf,
sscanf,
vscanf,
vsscanf,
vfscanf
—
input format conversion
LIBRARY
Standard C Library (libc, -lc)
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
dioux or n and the next pointer is a
pointer to a short int (rather than
int).
-
-
- 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).
-
-
- j
- Indicates that the conversion will be one of
dioux or n and the next pointer is a
pointer to an intmax_t (rather than
int).
-
-
- l
- Indicates either that the conversion will be one of
dioux or n and the next pointer is a
pointer to a long int (rather than
int), or that the conversion will be one of
efg and the next pointer is a pointer to
double (rather than float).
-
-
- ll
- 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).
-
-
- q
- Indicates that the conversion will be one of
dioux or n and the next pointer is a
pointer to a quad_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).
-
-
- L
- Indicates that the conversion will be efg
and 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
NUL
character. 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
NUL
is 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
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.
-
-
- 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.