SCANF(S) XENIX System V SCANF(S)
Name
scanf, fscanf, sscanf - Converts and formats 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
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 cause input to be read up
to the next nonwhitespace 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, 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 *. 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
nonspace 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 preceding an input field is ignored.
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The conversion character 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 characters are
allowed:
% 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.
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
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 nonspace 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.
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 optionally signed integer.
[ 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
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entirely of characters in the scanset. The caret (^),
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 caret) 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, and x may be capitalized
and/or 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
capitalized and/or 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.
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 conflicting
character is left unread in the input stream.) This is very
important to remember, because subtle errors can occur when
not taking this into account.
scanf 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 i; float x; char name[50];
scanf ("%d%f%s", &i, &x, name);
with the input line:
25 54.32E-1 thompson
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will assign to i the value 25, to 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 (see getc(S))
will return ``a''.
See Also
atof(S), getc(S), printf(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
The success of literal matches and suppressed assignments is
not directly determinable.
Trailing whitespace (including a newline) is left unread
unless matched in the control string.
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