Question

我有一些lisp数字符串字符串要解析为数字：

＆＃34; 3.000000000E + 00＆＃34;
  ＆＃34; 0.0d0＆＃34;
  ＆＃34; 3＆＃34;

Answer 1

请使用Quicklisp提供的parse-number库。

Answer 2

(define-condition argument-not-numeric-string (error)
  ((text :initarg :text :reader text)))

(defun string-to-number (str &optional (radix 10))
  (let* ((*read-base* radix)
         (value (and (stringp str)                      
                     (ignore-errors
                      (with-input-from-string (in str)
                        (read in))))))
    (if (numberp value)
        value
        (flet ((read-new-value () (format t "Enter new value: ") (multiple-value-list (eval (read)))))
          (restart-case (error 'argument-not-numeric-string :text "Argument needs to be a string with an numeric value")
            (use-value (value) :interactive read-new-value (progn (assert (numberp value) (value) "value isn't numeric") value))
            (restart-with-string (string) :interactive read-new-value (string-to-number string radix)))))))

以下是测试：

(string-to-number "3.000000000E+00") ; ==> 3.0
(string-to-number "0.0d0")           ; ==> 0.0d0
(string-to-number "3")               ; ==> 3

(handler-bind ((argument-not-numeric-string #'(lambda (c) (invoke-restart 'restart-with-string "0"))))
  (string-to-number "hello")) ; ==> 0

(handler-bind ((argument-not-numeric-string #'(lambda (c) (use-value 0))))
  (string-to-number "hello")) ; ==> 0

(string-to-number "aa" 16) ; ==> 170

(string-to-number "gf" 16) 
*** - Condition of type ARGUMENT-NOT-NUMERIC-STRING.
The following restarts are available:
USE-VALUE      :R1      USE-VALUE
RESTART-WITH-STRING :R2 RESTART-WITH-STRING
ABORT          :R3      Abort main loop
Break 1 [50]> :r2
Enter new value: "ff"
; ==> 255

Answer 3

google之后，请参阅post：

* (with-input-from-string (in "3.000000000E+00")
    (read in))

3.0
*

lisp如何将不同数字的字符串解析为数字

3 个答案: