- 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.