scanf(3S)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, ...);
DESCRIPTIONscanf 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 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. If there are
insufficient arguments for the format, the behavior is undefined. 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, newlines, 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 character % 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, by l if it is a pointer to long
int or by ll if it is a pointer to a long 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, by l if it is a pointer
to unsigned long int, or by ll if it is a pointer to a unsigned
long long int. The conversion specifiers e, f, and g should be
preceded by l if the corresponding argument is a pointer to
double rather than a pointer to float. The conversion
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specifiers e, f, and g should be preceded by L if the
corresponding argument is a pointer to long double rather than a
pointer to float. Finally, the conversion specifiers c and s
should be preceded by l if the corresponding argument points to
an array of type wchar_t. This will result in the same behavior
as using the C and S specifiers (described below). The h, l,
ll, 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 suppression 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 inappropriate
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 following
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 format 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.
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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 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 argument should be a pointer to floating.
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 white-space
character.
S Same as s except that the corresponding argument should be a wchar_t
pointer pointing to an array of wchar_t large enough to accept the
string and a terminating \0, which will be added automatically.
c Matches a sequence of characters of the number specified 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.
C Same as c except that the corresponding argument should be a pointer
to the initial character of an array of type wchar_t large enough to
accept the sequence.
[ 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 characters 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
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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 bracket character is the
one that ends the specification.
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 character
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
character 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 predictable.
The conversion specifiers E, G, and X are also valid and behave the same
as e, g, and x, 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 LC_NUMERIC). 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.
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If conversion terminates on a conflicting input character, the offending
input character is left unread in the input stream. Trailing white space
(including newline 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 ALSOcc(1), strtod(3C), strtol(3C), printf(3S).
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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