SCANF(3C) Standard C Library Functions SCANF(3C)

NAME

scanf, fscanf, sscanf, vscanf, vfscanf, vsscanf - convert formatted input

SYNOPSIS

#include <stdio.h>

int scanf(const char *restrict format...);


int fscanf(FILE *restrict stream, const char *restrict format...);


int sscanf(const char *restrict s, const char *restrict format...);


#include <stdarg.h>
#include <stdio.h>

int vscanf(const char *format, va_list arg);


int vfscanf(FILE *stream, const char *format, va_list arg);


int vsscanf(const char *s, const char *format, va_list arg);

DESCRIPTION

The scanf() function reads from the standard input stream stdin.


The fscanf() function reads from the named input stream.


The sscanf() function reads from the string s.


The vscanf(), vfscanf(), and vsscanf() functions are equivalent to the
scanf(), fscanf(), and sscanf() functions, respectively, except that
instead of being called with a variable number of arguments, they are
called with an argument list as defined by the <stdarg.h> header . These
functions do not invoke the va_end() macro. Applications using these
functions should call va_end(ap) afterwards to clean up.


Each function reads bytes, 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 result is
undefined if there are insufficient arguments for the format. If the
format is exhausted while arguments remain, the excess arguments are
evaluated but are otherwise ignored.


Conversions can be applied to the nth argument after the format in the
argument list, rather than to the next unused argument. In this case, the
conversion character % (see below) is replaced by the sequence %n$, where
n is a decimal integer in the range [1, NL_ARGMAX]. This feature provides
for the definition of format strings that select arguments in an order
appropriate to specific languages. In format strings containing the %n$
form of conversion specifications, it is unspecified whether numbered
arguments in the argument list can be referenced from the format string
more than once.


The format can contain either form of a conversion specification, that
is, % or %n$, but the two forms cannot normally be mixed within a single
format string. The only exception to this is that %% or %* can be mixed
with the %n$ form.


The scanf() function in all its forms allows for detection of a language-
dependent radix character in the input string. The radix character is
defined in the program's locale (category LC_NUMERIC). In the POSIX
locale, or in a locale where the radix character is not defined, the
radix character defaults to a period (.).


The format is a character string, beginning and ending in its initial
shift state, if any, composed of zero or more directives. Each directive
is composed of one of the following:

o one or more white-space characters (space, tab, newline,
vertical-tab or form-feed characters);

o an ordinary character (neither % nor a white-space character);
or

o a conversion specification.

Conversion Specifications

Each conversion specification is introduced by the character % or the
character sequence %n$, after which the following appear in sequence:

o An optional assignment-suppressing character *.

o An optional non-zero decimal integer that specifies the
maximum field width.

o An option length modifier that specifies the size of the
receiving object.

o A conversion specifier character that specifies the type of
conversion to be applied. The valid conversion characters are
described below.


The scanf() functions execute each directive of the format in turn. If a
directive fails, as detailed below, the function returns. Failures are
described as input failures (due to the unavailability of input bytes) or
matching failures (due to inappropriate input).


A directive composed of one or more white-space characters is executed by
reading input until no more valid input can be read, or up to the first
byte which is not a white-space character which remains unread.


A directive that is an ordinary character is executed as follows. The
next byte is read from the input and compared with the byte that
comprises the directive; if the comparison shows that they are not
equivalent, the directive fails, and the differing and subsequent bytes
remain unread.


A directive that is a conversion specification defines a set of matching
input sequences, as described below for each conversion character. A
conversion specification is executed in the following steps:


Input white-space characters (as specified by isspace(3C)) are skipped,
unless the conversion specification includes a [, c, C, or n conversion
character.


An item is read from the input unless the conversion specification
includes an n conversion character. The length of the item read is
limited to any specified maximum field width, which is interpreted in
either characters or bytes depending on the conversion character. In
Solaris default mode, the input item is defined as the longest sequence
of input bytes that forms a matching sequence. In some cases, scanf()
might need to read several extra characters beyond the end of the input
item to find the end of a matching sequence. In C99/SUSv3 mode, the input
item is defined as the longest sequence of input bytes that is, or is a
prefix of, a matching sequence. With this definition, scanf() need only
read at most one character beyond the end of the input item. Therefore,
in C99/SUSv3 mode, some sequences that are acceptable to strtod(3C),
strtol(3C), and similar functions are unacceptable to scanf(). In either
mode, scanf() attempts to push back any excess bytes read using
ungetc(3C). Assuming all such attempts succeed, the first byte, if any,
after the input item remains unread. If the length of the input item is
0, the conversion fails. This condition is a matching failure unless end-
of-file, an encoding error, or a read error prevented input from the
stream, in which case it is an input failure.


Except in the case of a % conversion character, the input item (or, in
the case of a %n conversion specification, the count of input bytes) is
converted to a type appropriate to the conversion character. If the input
item is not a matching sequence, the execution of the conversion
specification fails; this condition is a matching failure. Unless
assignment suppression was indicated by a *, the result of the conversion
is placed in the object pointed to by the first argument following the
format argument that has not already received a conversion result if the
conversion specification is introduced by %, or in the nth argument if
introduced by the character sequence %n$. If this object does not have an
appropriate type, or if the result of the conversion cannot be
represented in the space provided, the behavior is undefined.

Length Modifiers

The length modifiers and their meanings are:

hh
Specifies that a following d, i, o, u, x, X, or n
conversion specifier applies to an argument with type
pointer to signed char or unsigned char.


h
Specifies that a following d, i, o, u, x, X, or n
conversion specifier applies to an argument with type
pointer to short or unsigned short.


l (ell)
Specifies that a following d, i, o, u, x, X, or n
conversion specifier applies to an argument with type
pointer to long or unsigned long; that a following a, A,
e, E, f, F, g, or G conversion specifier applies to an
argument with type pointer to double; or that a following
c, s, or [ conversion specifier applies to an argument
with type pointer to wchar_t.


ll (ell-ell)
Specifies that a following d, i, o, u, x, X, or n
conversion specifier applies to an argument with type
pointer to long long or unsigned long long.


j
Specifies that a following d, i, o, u, x, X, or n
conversion specifier applies to an argument with type
pointer to intmax_t or uintmax_t.


z
Specifies that a following d, i, o, u, x, X, or n
conversion specifier applies to an argument with type
pointer to size_t or the corresponding signed integer
type.


t
Specifies that a following d, i, o, u, x, X, or n
conversion specifier applies to an argument with type
pointer to ptrdiff_t or the corresponding unsigned type.


L
Specifies that a following a, A, e, E, f, F, g, or G
conversion specifier applies to an argument with type
pointer to long double.


If a length modifier appears with any conversion specifier other than as
specified above, the behavior is undefined.

Conversion Characters

The following conversion characters are valid:

d
Matches an optionally signed decimal integer, whose format is
the same as expected for the subject sequence of strtol(3C)
with the value 10 for the base argument. In the absence of a
size modifier, the corresponding argument must be a pointer to
int.


i
Matches an optionally signed integer, whose format is the same
as expected for the subject sequence of strtol() with 0 for
the base argument. In the absence of a size modifier, the
corresponding argument must be a pointer to int.


o
Matches an optionally signed octal integer, whose format is
the same as expected for the subject sequence of strtoul(3C)
with the value 8 for the base argument. In the absence of a
size modifier, the corresponding argument must be a pointer to
unsigned int.


u
Matches an optionally signed decimal integer, whose format is
the same as expected for the subject sequence of strtoul()
with the value 10 for the base argument. In the absence of a
size modifier, the corresponding argument must be a pointer to
unsigned int.


x
Matches an optionally signed hexadecimal integer, whose format
is the same as expected for the subject sequence of strtoul()
with the value 16 for the base argument. In the absence of a
size modifier, the corresponding argument must be a pointer to
unsigned int.


a,e,f,g
Matches an optionally signed floating-point number, infinity,
or NaN, whose format is the same as expected for the subject
sequence of strtod(3C). In the absence of a size modifier, the
corresponding argument must be a pointer to float. The e, f,
and g specifiers match hexadecimal floating point values only
in C99/SUSv3 (see standards(7)) mode, but the a specifier
always matches hexadecimal floating point values.

These conversion specifiers match any subject sequence
accepted by strtod(3C), including the INF, INFINITY, NAN, and
NAN(n-char-sequence) forms. The result of the conversion is
the same as that of calling strtod() (or strtof() or
strtold()) with the matching sequence, including the raising
of floating point exceptions and the setting of errno to
ERANGE, if applicable.


s
Matches a sequence of bytes that are not white-space
characters. The corresponding argument must be a pointer to
the initial byte of an array of char, signed char, or unsigned
char large enough to accept the sequence and a terminating
null character code, which will be added automatically.

If an l (ell) qualifier is present, the input is a sequence of
characters that begins in the initial shift state. Each
character is converted to a wide-character as if by a call to
the mbrtowc(3C) function, with the conversion state described
by an mbstate_t object initialized to zero before the first
character is converted. The corresponding argument must be a
pointer to an array of wchar_t large enough to accept the
sequence and the terminating null wide-character, which will
be added automatically.


[
Matches a non-empty sequence of characters from a set of
expected characters (the scanset). The normal skip over white-
space characters is suppressed in this case. The corresponding
argument must be a pointer to the initial byte of an array of
char, signed char, or unsigned char large enough to accept the
sequence and a terminating null byte, which will be added
automatically.

If an l (ell) qualifier is present, the input is a sequence of
characters that begins in the initial shift state. Each
character in the sequence is converted to a wide-character as
if by a call to the mbrtowc() function, with the conversion
state described by an mbstate_t object initialized to zero
before the first character is converted. The corresponding
argument must be a pointer to an array of wchar_t large enough
to accept the sequence and the terminating null wide-
character, which will be added automatically.

The conversion specification includes all subsequent
characters in the format string up to and including the
matching right square bracket (]). The characters between the
square brackets (the scanlist) comprise the scanset, unless
the character after the left square 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 square bracket. If the conversion specification begins
with [] or [^], the right square bracket is included in the
scanlist and the next right square bracket is the matching
right square bracket that ends the conversion specification;
otherwise the first right square bracket is the one that ends
the conversion specification. If a - is in the scanlist and is
not the first character, nor the second where the first
character is a ^, nor the last character, it indicates a range
of characters to be matched.


c
Matches a sequence of characters of the number specified by
the field width (1 if no field width is present in the
conversion specification). The corresponding argument must be
a pointer to the initial byte of an array of char, signed
char, or unsigned char large enough to accept the sequence. No
null byte is added. The normal skip over white-space
characters is suppressed in this case.

If an l (ell) qualifier is present, the input is a sequence of
characters that begins in the initial shift state. Each
character in the sequence is converted to a wide-character as
if by a call to the mbrtowc() function, with the conversion
state described by an mbstate_t object initialized to zero
before the first character is converted. The corresponding
argument must be a pointer to an array of wchar_t large enough
to accept the resulting sequence of wide-characters. No null
wide-character is added.


p
Matches the set of sequences that is the same as the set of
sequences that is produced by the %p conversion of the
corresponding printf(3C) functions. The corresponding argument
must be a pointer to a pointer to void. If the input item is a
value converted earlier during the same program execution, the
pointer that results will compare equal to that value;
otherwise the behavior of the %p conversion is undefined.


n
No input is consumed. The corresponding argument must be a
pointer to the integer into which is to be written the number
of bytes read from the input so far by this call to the
scanf() functions. Execution of a %n conversion specification
does not increment the assignment count returned at the
completion of execution of the function.


C
Same as lc.


S
Same as ls.


%
Matches a single %; no conversion or assignment occurs. The
complete conversion specification must be %%.


If a conversion specification is invalid, the behavior is undefined.


The conversion characters A, E, F, G, and X are also valid and behave the
same as, respectively, a, e, f, g, and x.


If end-of-file is encountered during input, conversion is terminated. If
end-of-file occurs before any bytes matching the current conversion
specification (except for %n) have been read (other than leading white-
space characters, where permitted), execution of the current conversion
specification terminates with an input failure. Otherwise, unless
execution of the current conversion specification is terminated with a
matching failure, execution of the following conversion specification (if
any) is terminated with an input failure.


Reaching the end of the string in sscanf() is equivalent to encountering
end-of-file for fscanf().


If conversion terminates on a conflicting input, the offending input is
left unread in the input. Any trailing white space (including newline
characters) is left unread unless matched by a conversion specification.
The success of literal matches and suppressed assignments is only
directly determinable via the %n conversion specification.


The fscanf() and scanf() functions may mark the st_atime field of the
file associated with stream for update. The st_atime field will be marked
for update by the first successful execution of fgetc(3C), fgets(3C),
fread(3C), fscanf(), getc(3C), getchar(3C), gets(3C), or scanf() using
stream that returns data not supplied by a prior call to ungetc(3C).

RETURN VALUES

Upon successful completion, these functions return the number of
successfully matched and assigned input items; this number can be 0 in
the event of an early matching failure. If the input ends before the
first matching failure or conversion, EOF is returned. If a read error
occurs the error indicator for the stream is set, EOF is returned, and
errno is set to indicate the error.

ERRORS

For the conditions under which the scanf() functions will fail and may
fail, refer to fgetc(3C) or fgetwc(3C).


In addition, fscanf() may fail if:

EILSEQ
Input byte sequence does not form a valid character.


EINVAL
There are insufficient arguments.

USAGE

If the application calling the scanf() functions has any objects of type
wint_t or wchar_t, it must also include the header <wchar.h> to have
these objects defined.

EXAMPLES

Example 1: The call:

int i, n; float x; char name[50];
n = scanf("%d%f%s", &i, &x, name)


with the input line:


25 54.32E-1 Hamster


will assign to n the value 3, to i the value 25, to x the value 5.432,
and name will contain the string Hamster.

Example 2: The call:

int i; float x; char name[50];
(void) scanf("%2d%f%*d %[0123456789]", &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(3C) will return the character a.

ATTRIBUTES

See attributes(7) for descriptions of the following attributes:


+--------------------+-------------------+
|ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-------------------+
|CSI | Enabled |
+--------------------+-------------------+
|Interface Stability | Committed |
+--------------------+-------------------+
|MT-Level | MT-Safe |
+--------------------+-------------------+
|Standard | See standards(7). |
+--------------------+-------------------+

SEE ALSO

fgetc(3C), fgets(3C), fgetwc(3C), fread(3C), isspace(3C), printf(3C),
setlocale(3C), strtod(3C), strtol(3C), strtoul(3C), ungetc(3C),
wcrtomb(3C), attributes(7), standards(7)

NOTES

The behavior of the conversion specifier "%%" has changed for all of the
functions described on this manual page. Previously the "%%" specifier
accepted a "%" character from input only if there were no preceding
whitespace characters. The new behavior accepts "%" even if there are
preceding whitespace characters. This new behavior now aligns with the
description on this manual page and in various standards. If the old
behavior is desired, the conversion specification "%*[%]" can be used.

July 10, 2008 SCANF(3C)