Question

我想将文件内容读入列表。到目前为止，我的一些尝试都是 -

(defun get-file (filename)
  (let ((x (open filename)))
    (when x
      (loop for line = (read-line x nil)
     while line do (list line)))
    (close x)))

(defun get-file (filename)
  (let ((x (open filename :if-does-not-exist nil)) (contents (list nil)))
    (when x
      (loop for line = (read-line x nil)
     while line do (cons contents line)))
    (close x) contents))

(defun get-file (filename)
  (let ((x (open filename :if-does-not-exist nil)) (contents nil))
    (when x
      (loop for line = (read-line x nil)
     while line do (append contents line)))
    (close x) contents))

这些都没有奏效。谁能告诉我一个方法？或者甚至更好 - 如何将所有内容放入数组中？

Answer 1

怎么样

(defun get-file (filename)
  (with-open-file (stream filename)
    (loop for line = (read-line stream nil)
          while line
          collect line)))

Answer 2

问题出在哪里？

(defun get-file (filename)
  (let ((x (open filename)))
    (when x
      (loop for line = (read-line x nil)
            while line
            do (list line)))    ; <-- you are not collecting, just doing
    (close x)))                 ; <- the function returns the value of CLOSE

(defun get-file (filename)
  (let ((x (open filename :if-does-not-exist nil))
        (contents (list nil)))
    (when x
      (loop for line = (read-line x nil)
            while line
            do (cons contents line)))  ; <-- again, the cons goes nowhere
    (close x) contents))               ; <-- CONTENTS has never been changed

(defun get-file (filename)
  (let ((x (open filename :if-does-not-exist nil))
        (contents nil))
    (when x
      (loop for line = (read-line x nil)
            while line
            do (append contents line)))  ; <- again the result goes nowhere
    (close x) contents))                 ; <-- CONTENTS has never been changed

DO只会执行副作用。

COLLECT将收集结果，然后LOOP将在退出时返回收集值的列表。

如前所述，使用WITH-OPEN-FILE而不是OPEN / CLOSE。 WITH-OPEN-FILE将在离开动态范围时关闭文件。不仅从正常退出，而且在使用UNWIND-PROTECT的错误条件下。

如果要读取文件的内容，可以使用READ-SEQUENCE。与平常的问题。例如，当您将ASCII文件作为文本读入字符串时，该字符串可能比文件短。例如，Common Lisp将在CRLF为换行符的平台上用单个字符表示内部CRLF。另一个例子：在支持Unicode的实现中，文件中的UTF-8代码可能被替换为单个字符。

Answer 3

我将添加库。

修改更简单，使用uiop，包含在ASDF中：

(uiop:read-file-lines "file.txt")

https://github.com/fare/asdf/blob/master/uiop/stream.lisp#L445

也有

(uiop:read-file-string "file")

使用Alexandria's read-file-into-string和拆分序列：

(alexandria:read-file-into-string "file.txt")
(split-sequence:split-sequence #\Newline *)

使用str：

(str:lines (str:from-file "file.txt"))

如何将文件内容读入Lisp中的列表？

3 个答案: