SCANF
Section: Linux Programmer's Manual (3)
Updated: 29 November 1993
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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 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).
- 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).
- L
-
Indicates that the conversion will be
efg
and the next pointer is a pointer to
long double.
(This type is not implemented; the
L
flag is currently ignored---this may not be true for Linux.)
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 a signed hexadecimal integer; the next pointer must
be a pointer to
unsigned int.
- X
-
Equivalent to
lx;
this violates the ANSI C3.159-1989 (``ANSI C'') but is backwards compatible
with previous UNIX systems---I don't know what Linux does with this.
- 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
lf;
this violates the ANSI C3.159-1989 (``ANSI C'')
but is backwards compatible with previous UNIX
systems---I don't know what Linux does with this.
- F
-
Equivalent to
lf;
this exists only for backwards compatibility.
- 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
F
and
X
conversions will be changed in the future to conform to the
ANSI C standard, after which they will act like
f
and
x
respectively. The behavior of Linux on the non-standard points is not
known by this documenter.
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
strtol(3), strtoul(3), strtod(3), getc(3), printf(3)
STANDARDS
The functions
fscanf,
scanf,
and
sscanf
conform to ANSI C3.159-1989 (``ANSI C'').
BUGS
Differences for Linux are not known at this time. The following is for the
BSD version:
The current situation with
%F
and
%X
conversions is unfortunate.
All of the backwards compatibility formats will be removed in the future.
Numerical strings are truncated to 512 characters; for example,
%f
and
%d
are implicitly
%512f
and
%512d.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- CONVERSIONS
-
- RETURN VALUES
-
- SEE ALSO
-
- STANDARDS
-
- BUGS
-
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