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make-string-output-stream

make-string-output-stream Function

Syntax:

make-string-output-stream &key element-type → string-stream

Arguments and Values:

element-type—a type specifier . The default is character.

string-stream—an output string stream.

Description:

Returns an output string stream that accepts characters and makes available (via get-output-stream-string) a string that contains the characters that were actually output.

The element-type names the type of the elements of the string; a string is constructed of the most specialized type that can accommodate elements of that element-type.

Examples:

(let ((s (make-string-output-stream))) 
  (write-string "testing... " s) 
  (prin1 1234 s) 
  (get-output-stream-string s)) 
→ "testing... 1234" 
None..

See Also:

get-output-stream-string, with-output-to-string

Expanded Reference: make-string-output-stream​

Basic Usage​

make-string-output-stream creates an output stream that collects characters into a string, which can later be retrieved with get-output-stream-string.

(let ((s (make-string-output-stream)))
  (write-string "hello " s)
  (write-string "world" s)
  (get-output-stream-string s))
=> "hello world"

Building Strings with Multiple Operations​

Various output functions can write to a string output stream.

(let ((s (make-string-output-stream)))
  (write-string "testing... " s)
  (prin1 1234 s)
  (get-output-stream-string s))
=> "testing... 1234"

Clearing on Retrieval​

Calling get-output-stream-string clears the stream, so subsequent calls return only newly written content.

(let ((s (make-string-output-stream)))
  (write-string "first" s)
  (let ((r1 (get-output-stream-string s)))
    (write-string "second" s)
    (let ((r2 (get-output-stream-string s)))
      (list r1 r2))))
=> ("first" "second")

Using with format​

format can direct output to a string output stream.

(let ((s (make-string-output-stream)))
  (format s "~D item~:P at ~,2F each" 3 9.5)
  (get-output-stream-string s))
=> "3 items at 9.50 each"

Stream Properties​

A string output stream is an output stream but not an input stream.

(let ((s (make-string-output-stream)))
  (list (output-stream-p s)
        (input-stream-p s)
        (streamp s)))
=> (T NIL T)