| SCANF(3) | Library Functions Manual | SCANF(3) |
fscanf, scanf,
sscanf, vfscanf,
vscanf, vsscanf —
input format conversion
Standard C Library (libc, -lc)
#include
<stdio.h>
int
fscanf(FILE *restrict stream,
const char *restrict format,
...);
int
scanf(const char *restrict
format, ...);
int
sscanf(const char *restrict s,
const char *restrict format,
...);
#include
<stdarg.h>
#include <stdio.h>
int
vfscanf(FILE *restrict stream,
const char *restrict format, va_list
arg);
int
vscanf(const char *restrict
format, va_list arg);
int
vsscanf(const char *restrict s,
const char *restrict format, va_list
arg);
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
s.
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).
Extended locale versions of these functions are documented in scanf_l(3). See xlocale(3) for more information.
Following the % character introducing a
conversion, there may be a number of
flag
characters, as follows:
*hhdioux
or n and the next pointer is a pointer to a
char (rather than int).hdioux
or n and the next pointer is a pointer to a
short int (rather than
int).l
(ell)dioux
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)dioux
or n and the next pointer is a pointer to a
long long int (rather than
int).La,
e, f, or
g and the next pointer is a pointer to
long double.jdioux
or n and the next pointer is a pointer to a
intmax_t (rather than
int).tdioux
or n and the next pointer is a pointer to a
ptrdiff_t (rather than
int).zdioux
or n and the next pointer is a pointer to a
size_t (rather than int).qdioux 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:
%%’. That is,
“%%” in the format string matches a
single input ‘%’ character. No
conversion is done, and assignment does not occur.di0x’ or
‘0X’, in base 8 if it begins with
‘0’, and in base 10 otherwise. Only
characters that correspond to the base are used.oux,
Xa,
A, e,
E, f,
F, g,
Gl
or L is specified.)sNUL 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).
Sls.cNUL 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).
Clc.[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, with a circumflex, in) set or when the field width runs out.
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).
p%p’ in
printf(3)); the next pointer must be
a pointer to void * (or other pointer type).n* 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.
These functions return the number of input items assigned. This
can be fewer than provided for, or even zero, in the event of a matching
failure. Zero indicates that, although 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.
getc(3), mbrtowc(3), printf(3), scanf_l(3), strtod(3), strtol(3), strtoul(3), wscanf(3)
The functions fscanf(),
scanf(), sscanf(),
vfscanf(), vscanf(), and
vsscanf() conform to ISO/IEC
9899:1999 (“ISO C99”).
Earlier implementations of fscanf treated
%D, %E,
%F, %O and
%X as their lowercase equivalents with an
l modifier. In addition,
fscanf 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 fscanf family of functions do not
correctly handle multibyte characters in the format
argument.
| January 4, 2003 | macOS 15.0 |