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ActiveTcl User Guide |
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- NAME
- scan - Parse string using conversion specifiers in the style of
sscanf
- SYNOPSIS
- scan string format ?varName varName
...?
- INTRODUCTION
- DETAILS ON SCANNING
- d
- o
- x
- u
- i
- c
- s
- e or f 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 fields from an input string in the same fashion
as 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 field is scanned from string the result is converted
back into a string and 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 isn't 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 *, which indicates that
the converted value is to be discarded instead of assigned to a
variable; a XPG3 position specifier; a number indicating a maximum
field width; a field 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 specifier 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 following conversion characters are supported:
- d
- The input field must be a decimal integer. It is read in and
the value is stored in the variable as a decimal string. If the
l or L field size modifier is given, the scanned
value will have an internal representation that is at least 64-bits
in size.
- o
- The input field must be an octal integer. It is read in and the
value is stored in the variable as a decimal string. If the
l or L field size modifier is given, the scanned
value will have an internal representation that is at least 64-bits
in size. If the value exceeds MAX_INT (017777777777 on platforms
using 32-bit integers when the l and L modifiers are
not given), it will be truncated to a signed integer. Hence,
037777777777 will appear as -1 on a 32-bit machine by default.
- x
- The input field must be a hexadecimal integer. It is read in
and the value is stored in the variable as a decimal string. If the
l or L field size modifier is given, the scanned
value will have an internal representation that is at least 64-bits
in size. If the value exceeds MAX_INT (0x7FFFFFFF on platforms
using 32-bit integers when the l and L modifiers are
not given), it will be truncated to a signed integer. Hence,
0xFFFFFFFF will appear as -1 on a 32-bit machine.
- u
- The input field must be a decimal integer. The value is stored
in the variable as an unsigned decimal integer string. If the
l or L field size modifier is given, the scanned
value will have an internal representation that is at least 64-bits
in size.
- i
- The input field must be an integer. The base (i.e. decimal,
octal, or hexadecimal) is determined in the same fashion as
described in expr. The
value is stored in the variable as a decimal string. If the
l or L field size modifier is given, the scanned
value will have an internal representation that is at least 64-bits
in size.
- c
- A single character is read in and its binary value is stored in
the variable as a decimal string. Initial white space is not
skipped in this case, so the input field may be a white-space
character. This conversion is different from the ANSI standard in
that the input field always consists of a single character and no
field width may be specified.
- s
- The input field consists of all the characters up to the next
white-space character; the characters are copied to the
variable.
- e or f or g
- The input field 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 string.
- [chars]
- The input field consists of any number of 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 field consists of any number of 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.
- 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 field
for a given conversion terminates either when a white-space
character is encountered or when the maximum field 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:
- [1]
- %p conversion specifier is not currently supported.
- [2]
- For %c conversions a single character value is converted
to a decimal string, which is then assigned to the corresponding
varName; no field width may be specified for this
conversion.
- [3]
- 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).
- [4]
- 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.
Parse a simple color specification of the form #RRGGBB using
hexadecimal conversions with field sizes:
set string "#08D03F"
scan $string "#%2x%2x%2x" r g b
Parse a HH:MM time string, noting that this avoids
problems with octal numbers by forcing interpretation as decimals
(if we did not care, we would use the %i conversion
instead):
set string "08:08" ;# *Not* octal!
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"
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.
Copyright © 1995-1997 Roger E. Critchlow Jr.