- NAME
- scan — Parse string using conversion specifiers in the style of
sscanf
- SYNOPSIS
- INTRODUCTION
- DETAILS ON
SCANNING
- OPTIONAL
POSITIONAL SPECIFIER
- OPTIONAL SIZE
MODIFIER
- MANDATORY
CONVERSION CHARACTER
- d
- o
- x or
X
- b
- u
- i
- c
- s
- e or
f or g or E or G
- [chars]
- [^chars]
- n
- DIFFERENCES
FROM ANSI SSCANF
- EXAMPLES
- SEE
ALSO
- KEYWORDS
scan — Parse string using conversion specifiers in the style of
sscanf
scan string format ?varName varName ...?
This command parses substrings from an input string in a fashion
similar to the ANSI C sscanf procedure and returns a count
of the number of conversions performed, or -1 if the end of the
input string is reached before any conversions have been performed.
String gives the input to be parsed and format
indicates how to parse it, using % conversion specifiers as
in sscanf. Each varName gives the name of a variable;
when a substring is scanned from string that matches a
conversion specifier, the substring is assigned to the
corresponding variable. If no varName variables are
specified, then scan works in an inline manner, returning
the data that would otherwise be stored in the variables as a list.
In the inline case, an empty string is returned when the end of the
input string is reached before any conversions have been performed.
Scan operates by scanning string and format
together. If the next character in format is a blank or tab
then it matches any number of white space characters in
string (including zero). Otherwise, if it is not a %
character then it must match the next character of string.
When a % is encountered in format, it indicates the
start of a conversion specifier. A conversion specifier contains up
to four fields after the %: a XPG3 position specifier (or a
* to indicate the converted value is to be discarded instead
of assigned to any variable); a number indicating a maximum
substring width; a size modifier; and a conversion character. All
of these fields are optional except for the conversion character.
The fields that are present must appear in the order given above.
When scan finds a conversion specifier in format,
it first skips any white-space characters in string (unless
the conversion character is [ or c). Then it converts
the next input characters according to the conversion specifier and
stores the result in the variable given by the next argument to
scan.
If the % is followed by a decimal number and a $, as
in “%2$d”, then the variable to use is not taken from the
next sequential argument. Instead, it is taken from the argument
indicated by the number, where 1 corresponds to the first
varName. If there are any positional specifiers in
format then all of the specifiers must be positional. Every
varName on the argument list must correspond to exactly one
conversion specifier or an error is generated, or in the inline
case, any position can be specified at most once and the empty
positions will be filled in with empty strings.
The size modifier field is used only when scanning a substring into
one of Tcl's integer values. The size modifier field dictates the
integer range acceptable to be stored in a variable, or, for the
inline case, in a position in the result list. The syntactically
valid values for the size modifier are h, l,
z, t, q, j, ll, and L.
The h size modifier value is equivalent to the absence of a
size modifier in the the conversion specifier. Either one indicates
the integer range to be stored is limited to the 32-bit range. The
L size modifier is equivalent to the ll size
modifier. Either one indicates the integer range to be stored is
unlimited. The l (or q or j) size modifier
indicates that the integer range to be stored is limited to the
same range produced by the wide() function of the
expr command. The z
and t modifiers indicate the integer range to be the same as
for either h or l, depending on the value of the
pointerSize element of the tcl_platform array.
The following conversion characters are supported:
- d
- The input substring must be a decimal integer. It is read in
and the integer value is stored in the variable, truncated as
required by the size modifier value.
- o
- The input substring must be an octal integer. It is read in and
the integer value is stored in the variable, truncated as required
by the size modifier value.
- x or X
- The input substring must be a hexadecimal integer. It is read
in and the integer value is stored in the variable, truncated as
required by the size modifier value.
- b
- The input substring must be a binary integer. It is read in and
the integer value is stored in the variable, truncated as required
by the size modifier value.
- u
- The input substring must be a decimal integer. The integer
value is truncated as required by the size modifier value, and the
corresponding unsigned value for that truncated range is computed
and stored in the variable as a decimal string.
- i
- The input substring must be an integer. The base (i.e. decimal,
octal, or hexadecimal) is determined by the C convention (leading 0
for octal; prefix 0x for hexadecimal). The integer value is stored
in the variable, truncated as required by the size modifier
value.
- c
- A single character is read in and its Unicode value is stored
in the variable as an integer value. Initial white space is not
skipped in this case, so the input substring may be a white-space
character.
- s
- The input substring consists of all the characters up to the
next white-space character; the characters are copied to the
variable.
- e or f or g or
E or G
- The input substring must be a floating-point number consisting
of an optional sign, a string of decimal digits possibly containing
a decimal point, and an optional exponent consisting of an e
or E followed by an optional sign and a string of decimal
digits. It is read in and stored in the variable as a
floating-point value.
- [chars]
- The input substring consists of one or more characters in
chars. The matching string is stored in the variable. If the
first character between the brackets is a ] then it is
treated as part of chars rather than the closing bracket for
the set. If chars contains a sequence of the form
a-b then any character between a and
b (inclusive) will match. If the first or last character
between the brackets is a -, then it is treated as part of
chars rather than indicating a range.
- [^chars]
- The input substring consists of one or more characters not in
chars. The matching string is stored in the variable. If the
character immediately following the ^ is a ] then it
is treated as part of the set rather than the closing bracket for
the set. If chars contains a sequence of the form
a-b then any character between a and
b (inclusive) will be excluded from the set. If the first or
last character between the brackets is a -, then it is
treated as part of chars rather than indicating a range
value.
- n
- No input is consumed from the input string. Instead, the total
number of characters scanned from the input string so far is stored
in the variable.
The number of characters read from the input for a conversion is
the largest number that makes sense for that particular conversion
(e.g. as many decimal digits as possible for %d, as many
octal digits as possible for %o, and so on). The input
substring for a given conversion terminates either when a
white-space character is encountered or when the maximum substring
width has been reached, whichever comes first. If a * is
present in the conversion specifier then no variable is assigned
and the next scan argument is not consumed.
The behavior of the scan command is the same as the behavior
of the ANSI C sscanf procedure except for the following
differences:
- %p conversion specifier is not supported.
- For %c conversions a single character value is
converted to a decimal string, which is then assigned to the
corresponding varName; no substring width may be specified
for this conversion.
- The h modifier is always ignored and the
l and L modifiers are ignored when converting real
values (i.e. type double is used for the internal
representation). The ll modifier has no sscanf
counterpart.
- If the end of the input string is reached before any
conversions have been performed and no variables are given, an
empty string is returned.
Convert a UNICODE character to its numeric value:
set char "x"
set value [scan $char %c]
Parse a simple color specification of the form #RRGGBB
using hexadecimal conversions with substring sizes:
set string "#08D03F"
scan $string "#%2x%2x%2x" r g b
Parse a HH:MM time string:
set string "08:08"
if {[scan $string "%d:%d" hours minutes] != 2} {
error "not a valid time string"
}
# We have to understand numeric ranges ourselves...
if {$minutes < 0 || $minutes > 59} {
error "invalid number of minutes"
}
Break a string up into sequences of non-whitespace characters
(note the use of the %n conversion so that we get skipping
over leading whitespace correct):
set string " a string {with braced words} + leading space "
set words {}
while {[scan $string %s%n word length] == 2} {
lappend words $word
set string [string range $string $length end]
}
Parse a simple coordinate string, checking that it is complete
by looking for the terminating character explicitly:
set string "(5.2,-4e-2)"
# Note that the spaces before the literal parts of
# the scan pattern are significant, and that ")" is
# the Unicode character \u0029
if {
[scan $string " (%f ,%f %c" x y last] != 3
|| $last != 0x0029
} then {
error "invalid coordinate string"
}
puts "X=$x, Y=$y"
An interactive session demonstrating the truncation of integer
values determined by size modifiers:
% scan 20000000000000000000 %d
2147483647
% scan 20000000000000000000 %ld
9223372036854775807
% scan 20000000000000000000 %lld
20000000000000000000
format, sscanf
conversion
specifier, parse,
scan
Copyright © 1993 The Regents of the University of
California.
Copyright © 1994-1996 Sun Microsystems, Inc.
Copyright © 2000 Scriptics Corporation.