SCANF(3) BSD 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 prop-
erly 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:
* Suppresses assignment. The conversion that follows occurs as usual, but no pointer is used; the result of the conversion is simply
discarded.
hh Indicates that the conversion will be one of dioux or n and the next pointer is a pointer to a char (rather than int).
h Indicates that the conversion will be one of dioux 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 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)
Indicates that the conversion will be one of dioux 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 dioux 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 dioux or n and the next pointer is a pointer to a ptrdiff_t (rather than int).
z Indicates that the conversion will be one of dioux 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 dioux 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 pro-
cessing 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 assign-
ment does not occur.
d Matches an optionally signed decimal integer; the next pointer must be a pointer to int.
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 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, which-
ever 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, 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 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 * flag.
The decimal point character is defined in the program's locale (category LC_NUMERIC).
For backwards compatibility, a ``conversion'' of '% ' 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 char-
acter, 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 success-
fully 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'').
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.
BSD
January 4, 2003 BSD