scanf(3C) Standard C Library Functions scanf(3C)
scanf, fscanf, sscanf, vscanf, vfscanf, vsscanf - convert formatted
input
#include <stdio.h>
int scanf(const char *format, ...);
int fscanf(FILE*stream, const char *format, ...);
int sscanf(const char *s, const char *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);
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 (see
stdarg(3HEAD)). 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 con‐
trol 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$,
where n is a decimal integer in the range [1, NL_ARGMAX]. This feature
provides for the definition of format strings that select arguments in
an order appropriate to specific languages. In format strings contain‐
ing the %n$ 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$, but the two forms cannot normally be mixed within a sin‐
gle format string. The only exception to this is that %% or %* can be
mixed with the %n$ form.
The scanf() function in all its forms allows for detection of a lan‐
guage-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 direc‐
tive is composed of one of the following:
· one or more white-space characters (space, tab, newline, verti‐
cal-tab or form-feed characters);
· an ordinary character (neither % nor a white-space character); or
· 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:
· An optional assignment-suppressing character *.
· An optional non-zero decimal integer that specifies the maximum
field width.
· An optional size modifier h, l (ell), ll (ell ell), or L indicat‐
ing the size of the receiving object. The conversion characters
d, i, and n must be preceded by h if the corresponding argument
is a pointer to short int rather than a pointer to int, by l
(ell) if it is a pointer to long int, or by ll (ell ell) if it is
a pointer to long long int. Similarly, the conversion characters
o, u, and x must be preceded by h if the corresponding argument
is a pointer to unsigned short int rather than a pointer to
unsigned int, by l (ell) if it is a pointer to unsigned long int,
or by ll (ell ell) if it is a pointer to unsigned long long int.
The conversion characters e, f, and g must be preceded by l (ell)
if the corresponding argument is a pointer to double rather than
a pointer to float, or by L if it is a pointer to long double.
Finally, the conversion characters c, s, and [ must be precede by
l (ell) if the corresponding argument is a pointer to wchar_t
rather than a pointer to a character type. If an h, l (ell), ll
(ell ell), or L appears with any other conversion character, the
behavior is undefined.
· A conversion 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 com‐
prises the directive; if the comparison shows that they are not equiva‐
lent, the directive fails, and the differing and subsequent bytes
remain unread.
A directive that is a conversion specification defines a set of match‐
ing 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. An input item is defined as the
longest sequence of input bytes (up to any specified maximum field
width, which may be measured in characters or bytes dependent on the
conversion character) which is an initial subsequence of a matching
sequence. The first byte, if any, after the input item remains unread.
If the length of the input item is 0, the execution of the conversion
specification 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 conver‐
sion 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 argu‐
ment 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.
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 modi‐
fier, 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 modi‐
fier, 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 mod‐
ifier, the corresponding argument must be a pointer to unsigned
int.
e,f,g Matches an optionally signed floating-point number, 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.
If the printf(3C) family of functions generates character string
representations for infinity and NaN (a 7858 symbolic entity
encoded in floating-point format) to support the ANSI/IEEE Std
754: 1985 standard, the scanf() family of functions will
recognize them as input.
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 charac‐
ter is converted to a wide-character as if by a call to the mbr‐
towc(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 ter‐
minating 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 char‐
acters 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 charac‐
ter 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 scan‐
list 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 con‐
version 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 charac‐
ter 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 corre‐
sponding printf(3C) functions. The corresponding argument must be
a pointer to a pointer to void. If the input item is a value con‐
verted 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 exe‐
cution of the function.
C Same as lc.
S Same as ls.
% Matches a single %; no conversion or assignment occurs. The com‐
plete conversion specification must be %%.
If a conversion specification is invalid, the behavior is undefined.
The conversion characters E, G, and X are also valid and behave the
same as, respectively, e, 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 exe‐
cution 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 encounter‐
ing 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 specifica‐
tion. 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).
Upon successful completion, these functions return the number of suc‐
cessfully 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.
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.
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.
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.
See attributes(5) for descriptions of the following attributes:
+-----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|MT-Level |MT-Safe |
|CSI |Enabled |
+-----------------------------+-----------------------------+
fgetc(3C), fgets(3C), fgetwc(3C), fread(3C), isspace(3C), printf(3C),
setlocale(3C), stdarg(3HEAD), strtod(3C), strtol(3C), strtoul(3C), wcr‐
tomb(3C), ungetc(3C), attributes(5)
SunOS 5.9 3 May 2001 scanf(3C)