SCANF(3S) (C Programming Language Utilities) SCANF(3S)
NAME
scanf, fscanf, sscanf - convert formatted input
SYNOPSIS
#include <stdio.h>
int scanf (format [ , pointer ] ... )
char *format;
int fscanf (stream, format [ , pointer ] ... )
FILE *stream;
char *format;
int sscanf (s, format [ , pointer ] ... )
char *s, *format;
DESCRIPTION
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 format, and stores the
results in its arguments. Each expects, as arguments, 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 simply ignored.
The control string usually contains conversion
specifications, which are used to direct interpretation of
input sequences. The control string may contain:
1. White-space characters (blanks, tabs, new-lines, or
form-feeds) which, except in two cases described below,
cause input to be read up to the next non-white-space
character.
2. An ordinary character (not %), which must match the next
character of the input stream.
3. Conversion specifications, consisting of the character %,
an optional assignment suppressing character *, an
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optional numerical maximum field width, an optional l
(ell) or h indicating the size of the receiving variable,
and a conversion code.
A conversion specification directs the conversion of the
next input field; the result is placed in the variable
pointed to by the corresponding argument, unless assignment
suppression 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 code 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 codes 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
corresponding 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
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conventions: a leading ``0'' implies octal; a leading
``0x'' implies hexadecimal; otherwise, decimal.
n stores in an integer argument the total number of
characters (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
corresponding argument, which should be a pointer to a
float. The input format for floating point numbers is
an optionally signed string of digits, possibly
containing a decimal point, followed by an optional
exponent field consisting of an E or an e, followed by
an optional +, -, or space, followed by an integer.
s a character string is expected; the corresponding
argument 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; the indicated number of characters is
read.
[ indicates string data and 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
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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 construction of the scanset. A
range of characters may be represented by the construct
first-last, thus [0123456789] 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 character
(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 automatically. 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.
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 stream.
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. If the input ends before the first conflict
or conversion, EOF is returned.
EXAMPLES
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The call:
int n ; float x; char name[50];
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[50];
(void) scanf("%i%2d%f%*d %[0-9] ", &j, &i, &x, name);
with input:
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(3S)] will return a. Or:
int i, j, s, e; char name[50];
(void) scanf("%i %i %n%s%n", &i, &j, &s, name, &e);
with input:
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(3S)]
will return a blank.
SEE ALSO
getc(3S), printf(3S), stdio(3S), strtod(3C), strtol(3C).
DIAGNOSTICS
These functions return EOF on end of input and a short count
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for missing or illegal data items.
CAVEATS
Trailing white space (including a new-line) is left unread
unless matched in the control string.
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