scanffscanfsscanfvscanfvsscanfvfscanf
- input format conversion
LIBRARY
Lb libc
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
Fa 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
Fa stream ,
and
sscanf ();
reads its input from the character string pointed to by
Fa str .
The
vfscanf ();
function
is analogous to
vfprintf(3)
and reads input from the stream pointer
Fa 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
Fa format
string
may also contain other characters.
White space (such as blanks, tabs, or newlines) in the
Fa 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.
hh
Indicates that the conversion will be one of
dioux
or
n
and the next pointer is a pointer to a
Vt char
(rather than
Vt int ) .
h
Indicates that the conversion will be one of
dioux
or
n
and the next pointer is a pointer to a
Vt short int
(rather than
Vt int ) .
l (ell)
Indicates that the conversion will be one of
dioux
or
n
and the next pointer is a pointer to a
Vt long int
(rather than
Vt int ) ,
that the conversion will be one of
a , e , f
or
g
and the next pointer is a pointer to
Vt double
(rather than
Vt float ) ,
or that the conversion will be one of
cs
or
[
and the next pointer is a pointer to an array of
Vt wchar_t
(rather than
Vt char ) .
ll (ell ell)
Indicates that the conversion will be one of
dioux
or
n
and the next pointer is a pointer to a
Vt long long int
(rather than
Vt int ) .
L
Indicates that the conversion will be one of
a , e , f
or
g
and the next pointer is a pointer to
Vt long double .
j
Indicates that the conversion will be one of
dioux
or
n
and the next pointer is a pointer to a
Vt intmax_t
(rather than
Vt int ) .
t
Indicates that the conversion will be one of
dioux
or
n
and the next pointer is a pointer to a
Vt ptrdiff_t
(rather than
Vt int ) .
z
Indicates that the conversion will be one of
dioux
or
n
and the next pointer is a pointer to a
Vt size_t
(rather than
Vt int ) .
q
(deprecated.)
Indicates that the conversion will be one of
dioux
or
n
and the next pointer is a pointer to a
Vt long long int
(rather than
Vt 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
lcls
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
Vt int .
i
Matches an optionally signed integer;
the next pointer must be a pointer to
Vt 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
Vt unsigned int .
u
Matches an optionally signed decimal integer;
the next pointer must be a pointer to
Vt unsigned int .
x , X
Matches an optionally signed hexadecimal integer;
the next pointer must be a pointer to
Vt 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
Vt float
(unless
l
or
L
is specified.)
s
Matches a sequence of non-white-space characters;
the next pointer must be a pointer to
Vt 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
Vt 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
Vt 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
Vt 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
Vt 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
Vt 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
Vt 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
Vt 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, 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.
The functions
fscanf (,);
scanf (,);
sscanf (,);
vfscanf (,);
vscanf ();
and
vsscanf ();
conform to
St -isoC-99 .
BUGS
Earlier implementations of
treated
%D , %E , %F , %O
and
%X
as their lowercase equivalents with an
l
modifier.
In addition,
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
family of functions do not correctly handle multibyte characters in the
Fa format
argument.
