term% cat index.txt SCANF(3S) SCANF(3S)
NAME
scanf, fscanf, sscanf - formatted input conversion
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, 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 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 op‐
tional 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 corre‐
sponding argument, unless assignment suppression was indicated by *.
An input field is defined as a string of non-space characters; it ex‐
tends 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 re‐
stricted 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 ‘\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. The normal skip over space characters is sup‐
pressed 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 a floating point number is expected; the next field is converted
f 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 char‐
acters making up the string. If the first character is not circum‐
flex (^), the input field is all characters until the first charac‐
ter not in the set between the brackets; if the first character af‐
ter the left bracket is ^, the input field is all characters until
the first character which is in the remaining set of characters be‐
tween the brackets. The corresponding argument must point to a
character array.
The conversion characters d, o and x may be capitalized or preceeded by
l to indicate that a pointer to long rather than to int is in the argu‐
ment list. Similarly, the conversion characters e or f may be capital‐
ized or preceded by l to indicate a pointer to double rather than to
float. The conversion characters d, o and x may be preceeded by h to
indicate a pointer to short rather than to int.
The scanf functions return the number of successfully matched and as‐
signed 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), getc(3), printf(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 di‐
rectly determinable.
SCANF(3S)