scan(n) Tcl Built-In Commands scan(n)______________________________________________________________________________NAMEscan - Parse string using conversion specifiers in the style of sscanf
SYNOPSISscan string format varName ?varName ...?
_________________________________________________________________INTRODUCTION
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 con‐
versions 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.
DETAILS ON SCANNING
Scan operates by scanning string and formatString together. If the
next character in formatString is a blank or tab then it matches any
number of white space characters in string (including zero). Other‐
wise, if it isn't a % character then it must match the next character
of string. When a % is encountered in formatString, it indicates the
start of a conversion specifier. A conversion specifier contains three
fields after the %: a *, which indicates that the converted value is to
be discarded instead of assigned to a variable; a number indicating a
maximum field width; and a conversion character. All of these fields
are optional except for the conversion character.
When scan finds a conversion specifier in formatString, it first skips
any white-space characters in string. 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. The following con‐
version 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.
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.
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.
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 vari‐
able.
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 con‐
taining 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.
[^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.
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 pos‐
sible for %o, and so on). The input field for a given conversion ter‐
minates 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.
DIFFERENCES FROM ANSI SSCANF
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 and %n conversion specifiers are not currently supported.
[2] For %c conversions a single character value is converted to a
decimal string, which is then assigned to the corresponding var‐
Name; no field width may be specified for this conversion.
[3] The l, h, and L modifiers are ignored; integer values are
always converted as if there were no modifier present and real
values are always converted as if the l modifier were present
(i.e. type double is used for the internal representation).
KEYWORDS
conversion specifier, parse, scanTclscan(n)