SCANF(S) UNIX System V SCANF(S)
Name
scanf, fscanf, sscanf - convert formatted input
Syntax
#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
The scanf function 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 that
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
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
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 - , 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 carat (^),
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 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 carat) 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.
The scanf function 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.
The scanf function 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
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(S)) 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(S))
will return a blank.
See Also
getc(S), printf(S), stdio(S), strtod(S), strtol(S)
Diagnostics
These functions return EOF on end of input and a short count
for missing or illegal data items.
Notes
Trailing white space (including a new-line) is left unread
unless matched in the control string.
fscanf, scanf and sscanf are conformant with:
AT&T SVID Issue 2, Select Code 307-127;
The X/Open Portability Guide II of January 1987;
ANSI X3.159-198X C Language Draft Standard, May 13,
1988;
IEEE POSIX Std 1003.1-1988 with C Standard Language-
Dependent System Support;
and NIST FIPS 151-1.
(printed 6/20/89)