array to string

What is the most efficient way to convert an array of bytes to string?

The only thing I can think of is creating a foreign string from the array and using fli:convert-from-foreign string.

It's the end of a long work day and I want to double-check.

	Thanks, Joel

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Re: array to string


On Sep 29, 2011, at 9:42 PM, Joel Reymont wrote:

> What is the most efficient way to convert an array of bytes to string?


This works but is there a better way?

PACKET> (subseq *buffer* 1 10)
#(111 112 101 110 112 111 107 101 114)

PACKET> (setq x *)
#(111 112 101 110 112 111 107 101 114)

PACKET> (fli:replace-foreign-array y x)
"openpoker"

PACKET> (type-of *buffer*)
(SIMPLE-ARRAY (UNSIGNED-BYTE 8) (4096))

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Re: array to string

On Fri, Sep 30, 2011 at 4:03 AM, Joel Reymont <joelr1@gmail.com> wrote:
>
>
> On Sep 29, 2011, at 10:02 PM, Joshua TAYLOR wrote:
>
>> CL-USER > (map 'string 'code-char #(111 112 101 110 112 111 107 101 114))
>> "openpoker"
>
>
> Obvious but slow?

You may want to look at flexi-streams:octets-to-string and
external-format:decode-external-string - these do the required
conversion from bytes to strings, but also allow you to specify a
character encoding.

Alternatively, if your byte array represents a UTF-8 string, the code
below, with suitable modifications, should be faster than either
flexi-streams:octets-to-string or
external-format:decode-external-string.

(defun reinterpret-string-as-utf8 (string)
  "Useful when a string has been generated from an external source,
where the source data has been interpreted as an 8-bit (direct)
encoding - e.g, :latin-1, but should have been interpreted as :utf-8."
  (declare (optimize (speed 3) (compilation-speed 0)
                     (debug 1) (safety 1)))
  (let ((output-chars-remaining 0)
        (output-accumulator 0))
    (with-output-to-string (s nil :element-type 'character)
      (flet ((output-byte (byte)
               (if (zerop output-chars-remaining)
                 (if (= (logand byte #x80) 0)
                   (write-char (code-char byte) s)
                   (cond ((= (logand byte #xe0) #xc0)
                          (setf output-accumulator (logand byte #x1f))
                          (setf output-chars-remaining 1))
                         ((= (logand byte #xf0) #xe0)
                          (setf output-accumulator (logand byte #x0f))
                          (setf output-chars-remaining 2))
                         ((= (logand byte #xf8) #xf0)
                          (setf output-accumulator (logand byte #x07))
                          (setf output-chars-remaining 3))
                         ((= (logand byte #xfc) #xf8)
                          (setf output-accumulator (logand byte #x03))
                          (setf output-chars-remaining 4))
                         ((= (logand byte #xe0) #xfe)
                          (setf output-accumulator (logand byte #x01))
                          (setf output-chars-remaining 5))
                         (t (error "Invalid UTF-8 byte ~A" byte))))
                 (progn
                   (assert (= (logand byte #xc0) #x80))
                   (setf output-accumulator (logior (ash output-accumulator 6)
                                                    (logand byte #x3f)))
                   (decf output-chars-remaining)
                   (when (zerop output-chars-remaining)
                     (write-char (code-char output-accumulator) s))))))
        (loop for c across string
              do (output-byte (char-code c))
              finally (assert (= output-chars-remaining 0)))))))

Re: array to string

Hi Joel,


On 30 sept. 2011, at 03:42, Joel Reymont <joelr1@gmail.com> wrote:

> What is the most efficient way to convert an array of bytes to string?

You should be able to do that with flexi-streams.

Ihttp://weitz.de/flexi-streams/


Best Regards,
Camille

>