scanf, fscanf, sscanf - formatted input conversion
int scanf(format [ , pointer... ] )
int fscanf(stream, format [ , pointer... ] )
int sscanf(s, format [ , pointer... ] )
char *s, *format;
SYSTEM V SYNOPSIS
The following are provided for XPG2 compatibility:
#define nl_scanf scanf
#define nl_fscanf fscanf
#define nl_sscanf sscanf
scanf() reads from the standard input stream stdin. fscanf() reads
from the named input stream. sscanf() reads from the character string
s. Each function reads characters, interprets them according to a for-
mat, and stores the results in its arguments. Each expects, as argu-
ments, a control string format, described below, and a set of pointer
arguments indicating where the converted input should be stored. The
results are undefined in there are insufficient args for the format.
If the format is exhausted while args remain, the excess args are sim-
The control string usually contains conversion specifications, which
are used to direct interpretation of input sequences. The control
string may contain:
o White-space characters (SPACE, TAB, or NEWLINE) which, except
in two cases described below, cause input to be read up to
the next non-white-space character.
o An ordinary character (not `%'), which must match the next
character of the input stream.
o Conversion specifications, consisting of the character `%' or
the character sequence %digit$, an optional assignment sup-
pressing character `*', an optional numerical maximum field
width, an optional l (ell) or h indicating the size of the
receiving variable, and a conversion code.
Conversion specifications are introduced by the character % or the
character sequence %digit$. A conversion specification directs the
conversion of the next input field; the result is placed in the vari-
able pointed to by the corresponding argument, unless assignment sup-
pression was indicated by `*'. The suppression of assignment provides
a way of describing an input field which is to be skipped. An input
field is defined as a string of non-space characters; it extends to the
next inappropriate character or until the field width, if specified, is
exhausted. For all descriptors except ``['' and ``c'', white space
leading an input field is ignored.
The conversion character indicates the interpretation of the input
field; the corresponding pointer argument must usually be of a
restricted type. For a suppressed field, no pointer argument is given.
The following conversion characters are legal:
% A single % is expected in the input at this point; no
assignment is done.
d A decimal integer is expected; the corresponding argument
should be an integer pointer.
u An unsigned decimal integer is expected; the correspond-
ing argument should be an unsigned integer pointer.
o An octal integer is expected; the corresponding argument
should be an integer pointer.
x A hexadecimal integer is expected; the corresponding
argument should be an integer pointer.
i An integer is expected; the corresponding argument should
be an integer pointer. It will store the value of the
next input item interpreted according to C conventions: a
leading ``0'' implies octal; a leading ``0x'' implies
hexadecimal; otherwise, decimal.
n Stores in an integer argument the total number of charac-
ters (including white space) that have been scanned so
far since the function call. No input is consumed.
e,f,g A floating point number is expected; the next field is
converted accordingly and stored through the correspond-
ing argument, which should be a pointer to a float. The
input format for floating point numbers is as described
for string_to_decimal(3), with fortran_conventions zero.
s A character string is expected; the corresponding argu-
ment should be a character pointer pointing to an array
of characters large enough to accept the string and a
terminating \0, which will be added automatically. The
input field is terminated by a white space character.
c A character is expected; the corresponding argument
should be a character pointer. The normal skip over
white space is suppressed in this case; to read the next
non-space character, use %1s. If a field width is given,
the corresponding argument should refer to a character
array, and the indicated number of characters is read.
[ Indicates string data; the normal skip over leading white
space is suppressed. The left bracket is followed by a
set of characters, which we will call the scanset, and a
right bracket; the input field is the maximal sequence of
input characters consisting entirely of characters in the
scanset. The circumflex (^), when it appears as the
first character in the scanset, serves as a complement
operator and redefines the scanset as the set of all
characters not contained in the remainder of the scanset
string. There are some conventions used in the construc-
tion of the scanset. A range of characters may be repre-
sented by the construct first-last, thus  may
be expressed [0-9]. Using this convention, first must be
lexically less than or equal to last, or else the dash
will stand for itself. The dash will also stand for
itself whenever it is the first or the last character in
the scanset. To include the right square bracket as an
element of the scanset, it must appear as the first char-
acter (possibly preceded by a circumflex) of the scanset,
and in this case it will not be syntactically interpreted
as the closing bracket. The corresponding argument must
point to a character array large enough to hold the data
field and the terminating \0, which will be added auto-
matically. At least one character must match for this
conversion to be considered successful.
The conversion characters d, u, o, x, and i may be preceded by l or h
to indicate that a pointer to long or to short rather than to int is in
the argument list. Similarly, the conversion characters e, f, and g
may be preceded by l to indicate that a pointer to double rather than
to float is in the argument list. The l or h modifier is ignored for
other conversion characters.
Avoid this common error: because printf(3V) does not require that the
lengths of conversion descriptors and actual parameters match, coders
sometimes are careless with the scanf() functions. But converting %f
to &double or %lf to &float does not work; the results are quite incor-
scanf() conversion terminates at EOF, at the end of the control string,
or when an input character conflicts with the control string. In the
latter case, the offending character is left unread in the input
scanf() returns the number of successfully matched and assigned input
items; this number can be zero in the event of an early conflict
between an input character and the control string. The constant EOF is
returned upon end of input. Note: this is different from 0, which means
that no conversion was done; if conversion was intended, it was frus-
trated by an inappropriate character in the input.
If the input ends before the first conflict or conversion, EOF is
returned. If the input ends after the first conflict or conversion,
the number of successfully matched items is returned.
Conversions can be applied to the nth argument in the argument list,
rather than the next unused argument. In this case, the conversion
character % (see below) is replaced by the sequence %digit$, where
digit is a decimal integer n in the range [1,9], giving the position of
the argument in the argument list. This feature provides for the defi-
nition of format strings that select arguments in an order appropriate
to specific languages.
The format string can contain either form of a conversion specifica-
tion, that is % or %digit$, although the two forms cannot be mixed
within a single format string.
All forms of the scanf() functions allow for the detection of a lan-
guage dependent radix character in the input string. The radix charac-
ter is defined by the program's locale (category LC_NUMERIC). In the
"C" locale, or in a locale where the radix character is not defined,
the radix character defaults to `.'.
SYSTEM V DESCRIPTION
FORMFEED is allowed as a white space character in control strings.
XPG2 requires that nl_scanf, nl_fscanf and nl_sscanf be defined as
scanf, fscanf and sscanf, respectively for backward compatibility.
If any items are converted, scanf(), fscanf() and sscanf() return the
number of items converted successfully. This number may smaller than
the number of items requested. If no items are converted, these func-
tions return 0. scanf(), fscanf() and sscanf() return EOF on end of
int i, n; float x; char name;
n = scanf("%d%f%s", &&i, &&x, name);
with the input line:
25 54.32E-1 thompson
will assign to n the value 3, to i the value 25, to x the value 5.432,
and name will contain thompson\0. Or:
int i, j; float x; char name;
(void) scanf("%i%2d%f%*d %[0-9]", &&j, &&i, &&x, name);
011 56789 0123 56a72
will assign 9 to j, 56 to i, 789.0 to x, skip 0123, and place the
string 56\0 in name. The next call to getchar() (see getc(3V)) will
return a. Or:
int i, j, s, e; char name;
(void) scanf("%i %i %n%s%n", &&i, &&j, &&s, name, &&e);
0x11 0xy johnson
will assign 17 to i, 0 to j, 6 to s, will place the string xy\0 in
name, and will assign 8 to e. Thus, the length of name is e - s = 2.
The next call to getchar() (see getc(3V)) will return a SPACE.
getc(3V), printf(3V), setlocale(3V), stdio(3V), string_to_decimal(3),
Trailing white space (including a NEWLINE) is left unread unless
matched in the control string.
The success of literal matches and suppressed assignments is not
21 January 1990 SCANF(3V)