sscanf(3C)
NAME
scanf, fscanf, sscanf, vscanf, vfscanf, vsscanf - convert
formatted input
SYNOPSIS
#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);
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 argu-
ment 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 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 for-
mat is exhausted while arguments remain, the excess argu-
ments 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 specifica-
tions, 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 specifi-
cation, 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 charac-
ter 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 follow-
ing:
o one or more white-space characters (space, tab, new-
line, 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 optional size modifier h, l (ell), ll (ell ell), or
L indicating 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.
o A conversion character that specifies the type of
conversion to be applied. The valid conversion charac-
ters are described below.
The scanf() functions execute each directive of the format
in turn. If a directive fails, as detailed below, the func-
tion 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 com-
parison 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. 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 charac-
ter) 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 match-
ing sequence, the execution of the conversion specification
fails; this condition is a matching failure. Unless assign-
ment 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 unde-
fined.
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 for-
mat 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.
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 char-
acter 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 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 automati-
cally.
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 con-
verted 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 speci-
fied by the field width (1 if no field width is
present in the conversion specification). The
corresponding argument must be a pointer to the ini-
tial 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 con-
verted 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 ear-
lier during the same program execution, the pointer
that results will compare equal to that value; other-
wise 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 writ-
ten 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 execu-
tion 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 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 specifica-
tion terminates with an input failure. Otherwise, unless
execution of the current conversion specification is ter-
minated 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 offend-
ing 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 suc-
cessful 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(5) for descriptions of the following attri-
butes:
____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
| MT-Level | MT-Safe |
| CSI | Enabled |
|_____________________________|_____________________________|
SEE ALSO
fgetc(3C), fgets(3C), fgetwc(3C), fread(3C), isspace(3C),
printf(3C), setlocale(3C), stdarg(3HEAD), strtod(3C),
strtol(3C), strtoul(3C), wcrtomb(3C), ungetc(3C), attri-
butes(5)
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