SCANF(3S) SCANF(3S)
NAME
scanf, fscanf, sscanf - formatted input
SYNOPSIS
#include <stdio.h>
scanf(format [ , pointer ] ... )
char *format;
fscanf(stream, format [ , pointer ] ... )
FILE *stream;
char *format;
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, inter-
prets 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 arguments, normally
pointers, indicating where the converted input should be
stored.
The control string usually contains conversion specifica-
tions, 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 *. Conversions other than `c'
and `[' skip white space and consume non-white-space charac-
ters up to the next inappropriate character or until the
field width, if specified, is exhausted. The field width is
either an integer constant or `!'. In the latter case, the
width is taken from an integer argument that precedes the
SCANF(3S) SCANF(3S)
next pointer argument.
The conversion character indicates the interpretation of the
input field; the corresponding pointer argument must usually
be of a restricted type. The following conversion charac-
ters are legal:
% A single `%' is expected in the input at this point; no
assignment is done.
d A decimal integer is expected; the corresponding argu-
ment should be an 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.
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. 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. 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 correspond-
ing 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.
[
[^ A character string is expected. The left bracket (or
bracket and circumflex) is followed by a set of charac-
ters and a right bracket. When the set is introduced by
[ (or [^), the string consists only of characters in (or
not in) the set. The corresponding argument must point
to a character array.
The conversion characters d, o and x may be 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 preceded by l to indicate a pointer to double rather
SCANF(3S) SCANF(3S)
than to float. The conversion characters d, o and x may be
preceded by h to indicate a pointer to short.
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 charac-
ter 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\0'. 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\0' in name. The next call to getchar will
return `a'.
SEE ALSO
atof(3), stdio(3), ungetc(3)
DIAGNOSTICS
The scanf 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.
The input scan stops short of the end of excessively long
numbers.
There is no `%#'.
When no maximum field width is given in a `%s' or `%[]' con-
version specification, improper input can overrun the output
string and corrupt the program in arbitrarily malicious
ways. The best alternative, `%!s', is nonstandard.
A deprecated usage allows upper-case conversion characters
as equivalents for lower-case characters preceded by `l'.