我想将一个文件的内容读入一个列表。到目前为止,我的一些尝试是 -
(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))
这些都不起作用。谁能告诉我一个方法?或者更好——如何将所有内容放入一个数组中?
怎么样
(defun get-file (filename)
(with-open-file (stream filename)
(loop for line = (read-line stream nil)
while line
collect line)))
我会添加库。
edit 使用
uiop
更容易,它包含在 ASDF 中:
(uiop:read-file-lines "file.txt")
https://common-lisp.net/project/asdf/uiop.html#UIOP_002fSTREAM
还有
(uiop:read-file-string "file")
read-file-into-string
和分裂序列:
(alexandria:read-file-into-string "file.txt")
(split-sequence:split-sequence #\Newline *)
与str:
(str:lines (str:from-file "file.txt"))
有关文件的更多食谱:https://lispcookbook.github.io/cl-cookbook/files.html
问题在哪里?
(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
循环
DO
的LOOP
子句只会执行一些副作用。
COLLECT
将收集结果,LOOP
然后将在退出时返回收集值列表。
打开和关闭文件
如前所述,使用
WITH-OPEN-FILE
代替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,而且在错误情况下,通过使用 UNWIND-PROTECT
来确保执行。
读取文件内容
如果你想读取一个文件的内容,你可以使用函数
READ-SEQUENCE
。与通常的问题。例如,当您将 ASCII 文件作为文本读入字符串时,字符串可能比文件短。例如,在 CRLF 是换行符的平台上,Common Lisp 将在内部用单个字符表示 CRLF。另一个例子:在 Unicode 支持实现中,文件中的 UTF-8 代码可能会被单个字符替换。
2023 更新
使用Transducer 模式可以很容易地处理文件的内容(或任何其他数据流)。具体对于一个文件:
(t:transduce #'t:pass #'t:cons #p"path/to/file.txt")
这会将给定文件中的每一行读入列表。请注意,没有太多理由这样做,因为之后您可能想在列表上执行的任何处理都可以在during 转换本身完成,从而避免一次将整个文件拉入内存的需要。
例如统计一个文件的字数:
(t:transduce (t:comp (t:map #'str:words) ;; (2) Split each line into a list of words.
#'t:concatenate) ;; (3) Flatten that list back into a single stream.
#'t:count ;; (4) Count the total number of split words.
#p"foobar.txt") ;; (1) Read from a file, one line at a time.
请注意,任一示例中的
t:
名称空间前缀都是假设在导入时已为库提供的昵称,如:
(:local-nicknames (#:t #:transducers))