scan(n) Tcl ( ) scan(n)
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NAME
scan - Parse string using conversion specifiers in the style
of sscanf
SYNOPSIS
scan string format varName ?varName ...?
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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 fields sucessfully parsed. 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 is ignored. Otherwise, if it isn't a % character then it
must match the next non-white-space 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.
x The input field must be a hexadecimal integer. It
is read in and the value is stored in the variable
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scan(n) Tcl ( ) scan(n)
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 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 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.
DIFFERENCES FROM ANSI SSCANF
The behavior of the scan command is the same as the behavior
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scan(n) Tcl ( ) scan(n)
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
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