binary - Insert and extract fields from binary strings

(Dissect and join binary data into/from tcl values)

    :   '''[binary format]''' ''formatString'' ?''arg arg ...''?

    :   '''[binary scan]''' ''string formatString'' ?''varName varName ...''?

    :   '''[binary encode]''' ''format'' ?''-option value ...''? ''data''

    :   '''[binary decode]''' ''format'' ?''-option value ...''? ''data''

http://purl.org/tcl/home/man/tcl8.5/TclCmd/binary.htm

----
This is the primary command to use when [Working with binary data].
For dealing with binary data on C level see also [http://www.tcl.tk/man/tcl8.5/TclLib/ByteArrObj.htm%|%the ByteArray manpage].
See [Binary representation of numbers] or [bitstrings] for examples of usage.

<<discussion>>

What are the issues when dealing with special values - 64 bits for instance?

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**Examples**

In a conversation in the Tcl'ers Chat about how to display the bits in a number [DKF] came up with this:

======
 binary scan [binary format I $value] B32 x; set x
======

[GPS]: I use the following string to/from hex 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
 }
======

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Q. Is there a way to display the [ASCII] equivalent of characters in a string?

A.

======
 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] character number (which is the same as the ASCII one for ASCII characters, and the same as the ISO8859-1 codepoint too, since UNICODE is a superset of ISO8859-1 and that 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} {
    set result ""
    foreach char [split $str ""] {
        append result [binary format b8 [binary scan $char B8 bits; set bits]]
    }
    return $result
}
======

<<discussion>>
----
**See also**
   * [encoding]
   * [format]
   * [scan]
   * For ''transfer'' encodings:
   ** [base64]
   ** [uuencode]
   ** [zlib]
<<categories>> Tcl syntax help | Command | Binary Data