binary , a built-in Tcl routine, performs byte-oriented operations on values.
binary interprets each character in a string as a byte value, i.e. a value between 0 and 255. binary scan extracts data from such values, and binary format generates such values. This is a sharp tool: If it encounters a character with a code point greater than 255, it simply ignores the extra bits, which can result in data loss if one isn't careful.
In a conversation in the Tcl Chatroom about how to display the bits in a number, DKF suggested this:
binary scan [binary format I $value] B32 x; set x
GPS: I use the following string to/from hexadecimal conversion procedures to store files that may contain special characters that interfere with the OS filesystem in my Grindweb program:
proc convert.string.to.hex str {
binary scan $str H* hex
return $hex
}
proc convert.hex.to.string hex {
foreach c [split $hex {}] {
if {![string is xdigit $c]} {
return "#invalid $hex"
}
}
binary format H* $hex
}Displaying the ascii equivalent of characters in a string:
set chrs abc binary scan [encoding convertto ascii $chrs] c* x puts $x 97 98 99
results in the translation of the characters to hex being assigned to $x. If the characters are some encoding other than ASCII, just change the ascii to the appropriate encoding name.
DKF: Also consider using scan $str %c for single characters where you want the unicode code point, which is the same as the ascii value for a character, and the same as the iso8859-1 codepoint too, since unicode is a superset of ISO8859-1, which in turn is a superset of ASCII.
AMG: Here's a way to reverse the bit order of each eight-bit character in a string:
proc bit_reverse {str} {
binary scan $str B* bits
binary format b* $bits
}PYK 2015-11-07: ::binary::^ might be the right name for a routine that does exclusive or operations on arbitrary strings. Here is an implementation of such a routine:
proc ::tcl::binary::^ {t1 t2} {
if {$t2 < $t1} {
set t1 $t2[set t2 $t1; list]
}
set step 256
set res {}
for {set i 0} {$i < [string length $t1]} {incr i $step} {
set end [expr {min($i+$step-1, [string length $t1]-1)}]
binary scan [string range $t1 $i $end] c* codes1
binary scan [string range $t2 $i $end] c* codes2
foreach c1 $codes1 c2 $codes2 {
if {$c1 eq {} || $c2 eq {}} {
break
}
append res [binary format c [::tcl::mathop::^ $c1 $c2]]
}
}
return $res
}
namespace ensemble configure ::binary -map [dict merge [
namespace ensemble configure ::binary -map] [
dict create ^ ::tcl::binary::^]]binaryscanr : A web-based Tcl binary scan command editor/tester app that help you learn and use the Tcl binary command by visualizing actions with your real data. The frontend is following common react + redux design pattern. The backend is implemented in Tcl + express.js that provides a simple API layer.