NAME
scanf, fscanf, sscanf - formatted input conversion

SYNOPSIS
#include <stdio.h>

int scanf(format [ , pointer ] . . . )
const char *format;

int fscanf(stream, format [ , pointer ] . . . )
FILE *stream;
const char *format;

int sscanf(s, format [ , pointer ] . . . )
const char *s, *format;

#include <varargs.h>
int vscanf(format, args)
const char *format;
va_list args;

int vfscanf(stream, format, args)
FILE *stream;
const char *format;
va_list args;

int vsscanf(s, format, args)
const char *s, *format;
va_list args;

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. Alternate forms, in which the arguments have
already been captured using the variable-length argument facilities
of varargs(3), are available under the names vscanf, vfscanf, and
vsscanf.

The control string usually contains conversion specifications,
which are used to direct interpretation of input sequences. The
control string may contain:

1. Blanks, tabs or newlines, which match optional white space in
the input.

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, and a conversion character.

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 *. 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.

The conversion character indicates the interpretation of the input
field; the corresponding pointer argument must usually be of a
restricted type. 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.

o an octal integer is expected; the corresponding argument should
be a integer pointer.

x a hexadecimal integer is expected; the corresponding argument
should be an integer pointer.

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
‘ ’, which will be added. The input field is terminated by a
space character or a newline.

c a character is expected; the corresponding argument should be a
character pointer. The normal skip over space characters is
suppressed in this case; to read the next non-space character,
try ‘%1s’. If a field width is given, the corresponding
argument should refer to a character array, and the indicated
number of characters is read.

e,f 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 e
followed by an optionally signed integer.

[ indicates a string not to be delimited by space characters.
The left bracket is followed by a set of characters and a right
bracket; the characters between the brackets define a set of
characters making up the string. If the first character is not
circumflex (^), the input field is all characters until the
first character not in the set between the brackets; if the
first character after the left bracket is ^, the input field is
all characters until the first character which is in the
remaining set of characters between the brackets. The
corresponding argument must point to a character array.

The conversion characters d, o and x may be capitalized or preceded
by l to indicate that a pointer to long rather than to int is in
the argument list. Similarly, the conversion characters e or f may
be capitalized or preceded by l to indicate a pointer to double
rather than to float. The conversion characters d, o and x may be
preceded by h to indicate a pointer to short rather than to int.

The scanf functions return the number of successfully matched and
assigned input items. This can be used to decide how many input
items were found. The constant EOF is returned upon end of input;
note that this is different from 0, which means that no conversion
was done; if conversion was intended, it was frustrated by an
inappropriate character in the input.

For example, the call

int i; float x; char name[50];
scanf("%d%f%s", &i, &x, name);

with the input line

25 54.32E-1 thompson

will assign to i the value 25, x the value 5.432, and name will
contain ‘thompson ’. Or,

int i; float x; char name[50];
scanf("%2d%f%*d%[1234567890]", &i, &x, name);

with input

56789 0123 56a72

will assign 56 to i, 789.0 to x, skip ‘0123’, and place the string
‘56 ’ in name. The next call to getchar will return ‘a’.