scanf(3S) STANDARD I/O FUNCTIONS scanf(3S)
NAME
scanf, fscanf, sscanf - convert formatted input
SYNOPSIS
#include <stdio.h>
int scanf(const char *format, ...);
int fscanf(FILE *strm, const char *format, ...);
int sscanf(const char *s, const char *format, ...);
DESCRIPTION
scanf reads from the standard input stream, stdin. fscanf
reads from the stream strm. sscanf reads from the character
string s. Each function reads characters, interprets them
according to a format, and stores the results in its argu-
ments. Each expects, as arguments, a control string, for-
mat, described below and a set of pointer arguments indicat-
ing where the converted input should be stored. If there are
insufficient arguments for the format, the behavior is unde-
fined. If the format is exhausted while arguments remain,
the excess arguments are simply ignored. 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, tabs, new-lines, or
form-feeds) that, except in two cases described
below, cause input to be read up to the next non-
white-space character.
2. An ordinary character (not %) that must match the
next character of the input stream.
3. Conversion specifications consisting of the charac-
ter % or the character sequence %digits$, an
optional assignment suppression character *, a
decimal digit string that specifies an optional
numerical maximum field width, an optional letter l
(ell), L, or h indicating the size of the receiving
object, and a conversion code. The conversion
specifiers d, i, and n should be preceded by h if
the corresponding argument is a pointer to short
int rather than a pointer to int, or by l if it is
a pointer to long int. Similarly, the conversion
specifiers o, u, and x should be preceded by h if
the corresponding argument is a pointer to unsigned
short int rather than a pointer to unsigned int, or
by l if it is a pointer to unsigned long int.
Finally, the conversion specifiers e, f, and g
should be preceded by l if the corresponding argu-
ment is a pointer to double rather than a pointer
to float, or by L if it is a pointer to long
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double. The h, l, or L modifier is ignored with
any other conversion specifier.
A conversion specification directs the conversion of the
next input field; the result is placed in the variable
pointed to by the corresponding argument unless assignment
suppression was indicated by the character *. The suppres-
sion of assignment provides a way of describing an input
field that is to be skipped. An input field is defined as a
string of non-space characters; it extends to the next inap-
propriate character or until the maximum field width, if
one is specified, is exhausted. For all descriptors except
the character [ and the character c, white space leading an
input field is ignored. Conversions can be applied to the
nth argument in the argument list, rather than to the next
unused argument. In this case, the conversion character %
(see above) is replaced by the sequence %digits$ where
digits is a decimal integer n, giving the position of the
argument in the argument list. The first such argument,
%1$, immediately follows format. The control string can
contain either form of a conversion specification, i.e., %
or %digits$, although the two forms cannot be mixed within a
single control string. 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 is given. The follow-
ing conversion codes are valid:
% A single % is expected in the input at this point; no
assignment is done.
d Matches an optionally signed decimal integer, whose
format is the same as expected for the subject sequence
of the strtol function with the value 10 for the base
argument. The corresponding argument should be a
pointer to integer.
u Matches an optionally signed decimal integer, whose
format is the same as expected for the subject sequence
of the strtoul function with the value 10 for the base
argument. The corresponding argument should be a
pointer to unsigned integer.
o Matches an optionally signed octal integer, whose for-
mat is the same as expected for the subject sequence of
the strtoul function with the value 8 for the base
argument. The corresponding argument should be a
pointer to unsigned integer.
x Matches an optionally signed hexadecimal integer, whose
format is the same as expected for the subject sequence
of the strtoul function with the value 16 for the base
argument. The corresponding argument should be a
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pointer to unsigned integer.
i Matches an optionally signed integer, whose format is
the same as expected for the subject sequence of the
strtol function with the value 0 for the base argument.
The corresponding argument should be a pointer to
integer.
n No input is consumed. The corresponding argument
should be a pointer to integer into which is to be
written the number of characters read from the input
stream so far by the call to the function. Execution
of a %n directive does not increment the assignment
count returned at the completion of execution of the
function.
e,f,g
Matches an optionally signed floating point number,
whose format is the same as expected for the subject
string of the strtod function. The corresponding argu-
ment should be a pointer to floating.
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 automatically. The
input field is terminated by a white-space character.
c Matches a sequence of characters of the number speci-
fied by the field width (1 if no field width is present
in the directive). The corresponding argument should
be a pointer to the initial character of an array large
enough to accept the sequence. No null character is
added. The normal skip over white space is suppressed.
[ Matches a nonempty sequence of characters from a set of
expected characters (the scanset). The corresponding
argument should be a pointer to the initial character
of an array large enough to accept the sequence and a
terminating null character, which will be added
automatically. The conversion specifier includes all
subsequent characters in the format string, up to and
including the matching right bracket (]). The charac-
ters between the brackets (the scanlist) comprise the
scanset, unless the character after the left bracket is
a circumflex (^), in which case the scanset contains
all characters that do not appear in the scanlist
between the circumflex and the right bracket. If the
conversion specifier begins with [] or [^], the right
bracket character is in the scanlist and the next right
bracket character is the matching right bracket that
ends the specification; otherwise the first right
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bracket character is the one that ends the specifica-
tion.
A range of characters in the scanset 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 character - will also stand
for itself whenever it is the first or the last charac-
ter in the scanlist. To include the right bracket as
an element of the scanset, it must appear as the first
character (possibly preceded by a circumflex) of the
scanlist and in this case it will not be syntactically
interpreted as the closing bracket. At least one char-
acter must match for this conversion to be considered
successful.
p Matches an implementation-defined set of sequences,
which should be the same as the set of sequences that
may be produced by the %p conversion of the printf
function. The corresponding argument should be a
pointer to void. The interpretation of the input item
is implementation-defined. If the input item is a value
converted earlier during the same program execution,
the pointer that results shall compare equal to that
value; otherwise, the behavior of the %p conversion is
undefined. If an invalid conversion character follows
the %, the results of the operation may not be predict-
able. The conversion specifiers E, G, and X are also
valid and, under the -Xa and -Xc compilation modes [see
cc(1)], behave the same as e, g, and x, respectively.
Under the -Xt compilation mode, E, G, and X behave the
same as le, lg, and lx, respectively. Each function
allows for detection of a language-dependent decimal
point character in the input string. The decimal point
character is defined by the program's locale (category
LCNUMERIC). In the "C" locale, or in a locale where
the decimal point character is not defined, the decimal
point character defaults to a period (.). The scanf
conversion terminates at end of file, at the end of the
control string, or when an input character conflicts
with the control string. If end-of-file is encountered
during input, conversion is terminated. If end-of-file
occurs before any characters matching the current
directive have been read (other than leading white
space, where permitted), execution of the current
directive terminates with an input failure; otherwise,
unless execution of the current directive is terminated
with a matching failure, execution of the following
directive (if any) is terminated with an input failure.
If conversion terminates on a conflicting input charac-
ter, the offending input character is left unread in
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the input stream. Trailing white space (including
new-line characters) is left unread unless matched by a
directive. The success of literal matches and
suppressed assignments is not directly determinable
other than via the %n directive.
EXAMPLES
The call to the function scanf:
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 to n the value 3, to i the value 25, to x the
value 5.432, and name will contain thompson\0. The call to
the function scanf:
int i; float x; char name[50];
(void) scanf ("%2d%f%*d %[0-9]", &i, &x, name);
with the input line:
56789 0123 56a72
will assign 56 to i, 789.0 to x, skip 0123, and place the
characters 56\0 in name. The next character read from stdin
will be a.
SEE ALSO
cc(1), printf(3S), strtod(3C), strtol(3C), strtoul(3C).
DIAGNOSTICS
These routines return the number of successfully matched and
assigned input items; this number can be zero in the event
of an early matching failure between an input character and
the control string. If the input ends before the first
matching failure or conversion, EOF is returned.
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