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SCANF(3) FreeBSD Library Functions Manual SCANF(3)
NAME
scanf, fscanf, sscanf, vscanf, vsscanf, vfscanf - input format conversion
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <stdio.h>
int
scanf(const char * restrict format, ...);
int
fscanf(FILE * restrict stream, const char * restrict format, ...);
int
sscanf(const char * restrict str, const char * restrict format, ...);
#include <stdarg.h>
int
vscanf(const char * restrict format, va_list ap);
int
vsscanf(const char * restrict str, const char * restrict format,
va_list ap);
int
vfscanf(FILE * restrict stream, const char * restrict format,
va_list ap);
DESCRIPTION
The scanf() family of functions scans input according to a format as
described below. This format may contain conversion specifiers; the
results from such conversions, if any, are stored through the pointer
arguments. The scanf() function reads input from the standard input
stream stdin, fscanf() reads input from the stream pointer stream, and
sscanf() reads its input from the character string pointed to by str.
The vfscanf() function is analogous to vfprintf(3) and reads input from
the stream pointer stream using a variable argument list of pointers (see
stdarg(3)). The vscanf() function scans a variable argument list from
the standard input and the vsscanf() function scans it from a string;
these are analogous to the vprintf() and vsprintf() functions
respectively. Each successive pointer argument must correspond properly
with each successive conversion specifier (but see the * conversion
below). All conversions are introduced by the % (percent sign)
character. The format string may also contain other characters. White
space (such as blanks, tabs, or newlines) in the format string match any
amount of white space, including none, in the input. Everything else
matches only itself. Scanning stops when an input character does not
match such a format character. Scanning also stops when an input
conversion cannot be made (see below).
CONVERSIONS
Following the % character introducing a conversion there may be a number
of flag characters, as follows:
h Indicates that the conversion will be one of bdioux or n and
the next pointer is a pointer to a short int (rather than
int).
l (ell) Indicates that the conversion will be one of bdioux or n and
the next pointer is a pointer to a long int (rather than
int), that the conversion will be one of a, e, f, or g and
the next pointer is a pointer to double (rather than float),
or that the conversion will be one of c, s or [ and the next
pointer is a pointer to an array of wchar_t (rather than
char).
ll (ell ell)
Indicates that the conversion will be one of bdioux or n and
the next pointer is a pointer to a long long int (rather than
int).
L Indicates that the conversion will be one of a, e, f, or g
and the next pointer is a pointer to long double.
j Indicates that the conversion will be one of bdioux or n and
the next pointer is a pointer to a intmax_t (rather than
int).
t Indicates that the conversion will be one of bdioux or n and
the next pointer is a pointer to a ptrdiff_t (rather than
int).
wN (where N is 8, 16, 32, or 64) Indicates that the conversion
will be one of bdioux or n and the next pointer is a pointer
to a intN_t (rather than int).
wfN (where N is 8, 16, 32, or 64) Indicates that the conversion
will be one of bdioux or n and the next pointer is a pointer
to a int_fastN_t (rather than int).
z Indicates that the conversion will be one of bdioux or n and
the next pointer is a pointer to a size_t (rather than int).
q (deprecated.) Indicates that the conversion will be one of
bdioux or n and the next pointer is a pointer to a long long
int (rather than int).
In addition to these flags, there may be an optional maximum field width,
expressed as a decimal integer, between the % and the conversion. If no
width is given, a default of "infinity" is used (with one exception,
below); otherwise at most this many bytes are scanned in processing the
conversion. In the case of the lc, ls and l[ conversions, the field
width specifies the maximum number of multibyte characters that will be
scanned. Before conversion begins, most conversions skip white space;
this white space is not counted against the field width.
The following conversions are available:
% Matches a literal `%'. That is, "%%" in the format string matches
a single input `%' character. No conversion is done, and
assignment does not occur.
b, B Matches an optionally signed binary integer; the next pointer must
`0b' or `0B', in base 16 if it begins with `0x' or `0X', in base 8
if it begins with `0', and in base 10 otherwise. Only characters
that correspond to the base are used.
o Matches an octal integer; the next pointer must be a pointer to
unsigned int.
u Matches an optionally signed decimal integer; the next pointer must
be a pointer to unsigned int.
x, X Matches an optionally signed hexadecimal integer; the next pointer
must be a pointer to unsigned int.
a, A, e, E, f, F, g, G
Matches a floating-point number in the style of strtod(3). The
next pointer must be a pointer to float (unless l or L is
specified.)
s Matches a sequence of non-white-space characters; the next pointer
must be a pointer to char, and the array must be large enough to
accept all the sequence and the terminating NUL character. The
input string stops at white space or at the maximum field width,
whichever occurs first.
If an l qualifier is present, the next pointer must be a pointer to
wchar_t, into which the input will be placed after conversion by
mbrtowc(3).
S The same as ls.
c Matches a sequence of width count characters (default 1); the next
pointer must be a pointer to char, and there must be enough room
for all the characters (no terminating NUL is added). The usual
skip of leading white space is suppressed. To skip white space
first, use an explicit space in the format.
If an l qualifier is present, the next pointer must be a pointer to
wchar_t, into which the input will be placed after conversion by
mbrtowc(3).
C The same as lc.
[ Matches a nonempty sequence of characters from the specified set of
accepted characters; the next pointer must be a pointer to char,
and there must be enough room for all the characters in the string,
plus a terminating NUL character. The usual skip of leading white
space is suppressed. The string is to be made up of characters in
(or not in) a particular set; the set is defined by the characters
between the open bracket [ character and a close bracket ]
character. The set excludes those characters if the first
character after the open bracket is a circumflex ^. To include a
close bracket in the set, make it the first character after the
open bracket or the circumflex; any other position will end the
set. The hyphen character - is also special; when placed between
two other characters, it adds all intervening characters to the
set. To include a hyphen, make it the last character before the
final close bracket. For instance, `[^]0-9-]' means the set
"everything except close bracket, zero through nine, and hyphen".
The string ends with the appearance of a character not in the (or,
pointer must be a pointer to void.
n Nothing is expected; instead, the number of characters consumed
thus far from the input is stored through the next pointer, which
must be a pointer to int. This is not a conversion, although it
can be suppressed with the * flag.
The decimal point character is defined in the program's locale (category
LC_NUMERIC).
For backwards compatibility, a "conversion" of `%\0' causes an immediate
return of EOF.
RETURN VALUES
These functions return the number of input items assigned, which can be
fewer than provided for, or even zero, in the event of a matching
failure. Zero indicates that, while there was input available, no
conversions were assigned; typically this is due to an invalid input
character, such as an alphabetic character for a `%d' conversion. The
value EOF is returned if an input failure occurs before any conversion
such as an end-of-file occurs. If an error or end-of-file occurs after
conversion has begun, the number of conversions which were successfully
completed is returned.
SEE ALSO
getc(3), mbrtowc(3), printf(3), strtod(3), strtol(3), strtoul(3),
wscanf(3)
STANDARDS
The functions fscanf(), scanf(), sscanf(), vfscanf(), vscanf() and
vsscanf() conform to ISO/IEC 9899:1999 ("ISO C99").
HISTORY
The functions scanf(), fscanf(), and sscanf() first appeared in Version 7
AT&T UNIX, and vscanf(), vsscanf(), and vfscanf() in 4.3BSD-Reno.
BUGS
Earlier implementations of scanf treated %D, %E, %F, %O and %X as their
lowercase equivalents with an l modifier. In addition, scanf treated an
unknown conversion character as %d or %D, depending on its case. This
functionality has been removed.
Numerical strings are truncated to 512 characters; for example, %f and %d
are implicitly %512f and %512d.
The %n$ modifiers for positional arguments are not implemented.
The scanf family of functions do not correctly handle multibyte
characters in the format argument.
FreeBSD 14.0-RELEASE-p11 September 5, 2023 FreeBSD 14.0-RELEASE-p11