scanf(3S) 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 format, and stores the results
in its arguments. Each function expects two arguments: a
control string format (described below) and a set of pointer
arguments indicating where the converted input should be
stored.
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 and tabs) 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 suppression 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 has been 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-white-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.
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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 should be 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.
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 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.
[ String data and the normal skip over leading white
space is suppressed. The left bracket is followed by
a set of characters (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
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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 circumflex)
of the scanset; otherwise it will be interpreted
syntactically 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, and x may be preceded by
l or h to indicate that a pointer to long or short, rather
than 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 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 when an early
conflict between an input character and the control string
occurs. If the input ends before the first conflict or
conversion, EOF is returned.
EXAMPLES
The call:
int i; 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 the value 3 to n, the value 25 to i, and the
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value 5.432 to x; name will contain thompson\0.
The call
int i; float x; char name[50];
(void) scanf ("%2d%f%*d %[0-9]", &i, &x, name);
with input
56789 0123 56a72
will assign 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.
SEE ALSO
getc(3S), printf(3S), strtod(3C), strtol(3C).
NOTE
Trailing white space is left unread unless matched in the
control string.
DIAGNOSTICS
These functions return EOF on end of input and a short count
for missing or illegal data items.
BUGS
The success of literal matches and suppressed assignments is
not directly determinable.
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