SCANF(3) Library Routines SCANF(3)
scanf, fscanf, sscanf, vscanf, vsscanf, vfscanf - input format conver-
int scanf (const char *format, ...);
int fscanf (FILE *stream, const char *format, ...);
int sscanf (const char *str, const char *format, ...);
int vscanf (const char *format, va_list ap);
int vsscanf (const char *str, const char *format, va_list ap);
int vfscanf (FILE *stream, const char *format, va_list ap);
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
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 func-
tion 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 'suppression' below). All
conversions are introduced by the % (percent sign) character. The for-
mat 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).
Following the % character introducing a conversion there may be a num-
ber of flag characters, as follows:
* Suppresses assignment. The conversion that follows
occurs as usual, but no pointer is used; the result of
the conversion is simply discarded.
h Indicates that the conversion will be one of dioux or n
and the next pointer is a pointer to a short int (rather
l Indicates either that the conversion will be one of dioux
or n and the next pointer is a pointer to a long int
(rather than int), or that the conversion will be one of
efg and the next pointer is a pointer to double (rather
L Indicates that the conversion will be efg and the next
pointer is a pointer to long double. (This type is not
implemented; the L flag is currently ignored.)
In addition to these flags, there may be an optional maximum field
width, expressed as a decimal integer, between the % and the conver-
sion. If no width is given, a default of 'infinity' is used (with one
exception, below); otherwise at most this many characters are scanned
in processing the conversion. Before conversion begins, most conver-
sions skip white space; this white space is not counted against the
The following conversions are available:
% Matches a literal '%'. That is, '%%' in the format
string matches a single input '%' character. No conver-
sion is done, and assignment does not occur.
d Matches an optionally signed decimal integer; the next
pointer must be a pointer to int.
D Equivalent to ld; this exists only for backwards compati-
i Matches an optionally signed integer; the next pointer
must be a pointer to int. The integer is read 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 corre-
spond to the base are used.
o Matches an octal integer; the next pointer must be a
pointer to unsigned int.
O Equivalent to lo; this exists for backwards compatibil-
u Matches an optionally signed decimal integer; the next
pointer must be a pointer to unsigned int.
x Matches an optionally signed hexadecimal integer; the
next pointer must be a pointer to unsigned int.
X Equivalent to lx; this violates the ANSI/C standard, but
is backwards compatible with previous UNIX systems.
f Matches an optionally signed floating-point number; the
next pointer must be a pointer to float.
e Equivalent to f.
g Equivalent to f.
E Equivalent to lf; this violates the ANSI/C standard, but
is backwards compatible with previous UNIX systems.
F Equivalent to lf; this exists only for backwards compati-
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
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.
[ Matches a nonempty sequence of characters from the speci-
fied 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 sup-
pressed. 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 char-
acters 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 char-
acter 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 circum-
flex, in) set or when the field width runs out.
p Matches a pointer value (as printed by %p in printf(3));
the next 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
For backwards compatibility, other conversion characters (except \0)
are taken as if they were %d or, if uppercase, %ld, and a 'conversion'
of %\0 causes an immediate return of EOF. The F and X conversions will
be changed in the future to conform to the ANSI/C standard, after which
they will act like f and x respectively.
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 fail-
ure. Zero indicates that, while there was input available, no conver-
sions were assigned; typically this is due to an invalid input charac-
ter, such as an alphabetic character for a %d conversion.
The value EOF is returned if an input failure occurs before any conver-
sion 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 suc-
cessfully completed is returned.
strtol(3), strtoul(3), strtod(3), getc(3), printf(3)
The functions fscanf, scanf, and sscanf conform to ANSI/C.
The functions vscanf, vsscanf and vfscanf are new to this release.
The ORCA/C stdio implementation also provides a %b format specifier,
for Pascal-type strings. This is not currently implemented.
The current situation with %F and %X conversions is unfortunate.
All of the backwards compatibility formats will be removed in the
Numerical strings are truncated to 512 characters; for example, %f and
%d are implicitly %512f and %512d.
GNO 15 September 1997 SCANF(3)
Man(1) output converted with