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.
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).
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).
j
Indicates that the conversion will be one of dioux or n and the next pointer is a pointer to an intmax_t (rather than int).
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 than float).
ll
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).
q
Indicates that the conversion will be one of dioux or n and the next pointer is a pointer to a quad_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).
L
Indicates that the conversion will be efg and the next pointer is a pointer to long double.
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 characters are scanned in processing the conversion. 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.
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 compatibility.
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.
O
Equivalent to lo; this exists for backwards compatibility.
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.
f
Matches an optionally signed floating-point number; the next pointer must be a pointer to float.
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.
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 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.
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.
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 format string specifier macros described in
inttypes(3) should be used for the standard “C99” fixed-size integers documented in
stdint(3).