scan(3Tcl)

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.

     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.


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