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.\" @(#)scanf.3 6.11 (Berkeley) 6/29/91
.Nd input format conversion
.Fn scanf "const char *format" ...
.Fn fscanf "FILE *stream" "const char *format" ...
.Fn sscanf "const char *str" "const char *format" ...
.Fn vscanf "const char *format" "va_list ap"
.Fn vsscanf "const char *str" "const char *format" "va_list ap"
.Fn vfscanf "FILE *stream" "const char *format" "va_list ap"
family of functions scans input according to a
.Em conversion specifiers ;
the results from such conversions, if any,
reads input from the standard input stream
reads input from the stream pointer
reads its input from the character string pointed to by
and reads input from the stream pointer
using a variable argument list of pointers (see
function scans a variable argument list from the standard input and
function scans it from a string;
argument must correspond properly with
each successive conversion specifier
(but see `suppression' below).
All conversions are introduced by the
(percent sign) character.
may also contain other characters.
White space (such as blanks, tabs, or newlines) in the
string match any amount of white space, including none, in the input.
when an input character does not match such a format character.
when an input conversion cannot be made (see below).
character introducing a conversion
The conversion that follows occurs as usual, but no pointer is used;
the result of the conversion is simply discarded.
Indicates that the conversion will be one of
and the next pointer is a pointer to a
Indicates either that the conversion will be one of
and the next pointer is a pointer to a
or that the conversion will be one of
and the next pointer is a pointer to
Indicates that the conversion will be
and the next pointer is a pointer to
(This type is not implemented; the
flag is currently ignored.)
In addition to these flags,
there may be an optional maximum field width,
expressed as a decimal integer,
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:
That is, `%\&%' in the format string
matches a single input `%' character.
No conversion is done, and assignment does not occur.
Matches an optionally signed decimal integer;
the next pointer must be a pointer to
this exists only for backwards compatibility.
Matches an optionally signed integer;
the next pointer must be a pointer to
The integer is read in base 16 if it begins
in base 8 if it begins with
and in base 10 otherwise.
Only characters that correspond to the base are used.
Matches an octal integer;
the next pointer must be a pointer to
this exists for backwards compatibility.
Matches an optionally signed decimal integer;
the next pointer must be a pointer to
Matches an optionally a signed hexadecimal integer;
the next pointer must be a pointer to
but is backwards compatible with previous
Matches an optionally signed floating-point number;
the next pointer must be a pointer to
but is backwards compatible with previous
this exists only for backwards compatibility.
Matches a sequence of non-white-space characters;
the next pointer must be a pointer to
and the array must be large enough to accept all the sequence and the
The input string stops at white space
or at the maximum field width, whichever occurs first.
the next pointer must be a pointer to
and there must be enough room for all the characters
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
the next pointer must be a pointer to
and there must be enough room for all the characters in the string,
The usual skip of leading white space is suppressed.
The string is to be made up of characters in
the set is defined by the characters between the open bracket
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
any other position will end the set.
when placed between two other characters,
it adds all intervening characters to the set.
make it the last character before the final close bracket.
means the set `everything except close bracket, zero through nine,
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.
Matches a pointer value (as printed by
the next pointer must be a pointer to
instead, the number of characters consumed thus far from the input
is stored through the next pointer,
which must be a pointer to
a conversion, although it can be suppressed with the
For backwards compatibility,
other conversion characters (except
are taken as if they were
causes an immediate return of
conversions will be changed in the future
after which they will act like
the number of input items assigned, which can be fewer than provided
for, or even zero, in the event of a matching failure.
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
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
the number of conversions which were successfully completed is returned.
The current situation with
conversions is unfortunate.
All of the backwards compatibility formats will be removed in the future.