scan(n) Tcl scan(n)
_________________________________________________________________
NAME
scan - Parse string using conversion specifiers in the style
of sscanf
SYNOPSIS
scan 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 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.
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). Otherwise, 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
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.
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.
Page 1 (printed 2/19/99)
scan(n) Tcl scan(n)
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 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.
[^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 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.
Page 2 (printed 2/19/99)
scan(n) Tcl scan(n)
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 varName; 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, scan
Page 3 (printed 2/19/99)
