球拍：登录到文件

Question

我正在写一个需要登录信息但我想将日志存储在文件中的球拍程序。我的第一个尝试是使用“with-logging-to-port”并使用“open-output-file”创建一个输出端口。

#lang racket 
(require racket/logging) 
(define (identity/log x) 
    (log-info "returning ~a" x) x) 

(with-logging-to-port (open-output-file "testing.txt") 
    (λ() (identity/log 4)) 'info) 

但是，当我打开文件后，它是空白的！另外，由于“open-output-file”给我一个文件已经存在的错误，我不能再运行一次以上。

Answer 1

打开与您的文件的标志'追加。例如：

(open-output-file "testing.txt" #:exists 'append) 

Answer 2

我很确定原因是您没有正确关闭文件。这应该工作：

(let ((out (open-output-file "testing.txt" 
          ; just to not get an error on consecutive runs 
          #:exists 'append))) 
    (with-logging-to-port out 
    (λ() (identity/log 4)) 'info) 
    (close-output-port out)) 

而不是做家政的，你可以使用call-with-output-file

(call-with-output-file "testing.txt" 
    (λ (out) 
    (with-logging-to-port out 
     (λ() (identity/log 4)) 'info)) 
    #:exists 'append) 

Answer 3

如果日志信息是一个字符串列表，说LST，还可以使用以下功能：

(display-lines-to-file lst "mylog.txt" 
    #:exists 'append) 

参见：https://docs.racket-lang.org/reference/Filesystem.html?q=lines-file#%28def._%28%28lib._racket%2Ffile..rkt%29._display-lines-to-file%29%29

(require racket/file) 
(display-lines-to-file lst  path     
    [ #:separator separator     
     #:mode mode-flag     
     #:exists exists-flag])  →  void? 

Answer 4

我给你我的日志FUNC的源：

(define my_logger (make-logger 'my-log)) 

(define logger_thread #f) 

(define (log fmt . content) 
    (log-message my_logger 'info "" (string-append (format-time (now)) " " (apply format (cons fmt content))))) 

(define (start-logger log_path) 
    (let ([r (make-log-receiver my_logger 'info)] 
     [riqi (format-riqi (now))]) 
    (set! logger_thread 
      (thread 
      (lambda() 
      (let ([log_dir (build-path log_path (substring riqi 0 4))]) 
       (when (not (directory-exists? log_dir)) 
       (make-directory log_dir)) 
       (with-output-to-file 
        (build-path log_path (substring riqi 0 4) riqi) #:exists 'append 
        (lambda() 
        (let loop() 
         (match (sync r) 
         [(vector l m v v1) 
          (printf "~a\n" v) 
          (flush-output)]) 
         (loop)))))))))) 

(define (restart-logger) 
    (kill-thread logger_thread) 
    (start-logger)) 

(define (launch-log-daemon log_path) 
    (start-logger log_path) 
    (thread 
    (lambda() 
    (let loop() 
     (sync 
     (alarm-evt (+ (current-inexact-milliseconds) (* 1000 60 60)))) 
     (when (= 0 (date-hour (seconds->date (current-seconds)))) 
     (restart-logger)) 
     (loop))))) 

在应用程序开始时，你应该运行：

(launch-log-daemon log_path) 

那么你可以使用它像这样：

(log "~a:~a" "some1" "some2") 

我使用日期作为日志文件的目录和名称，

当日期改变时它会自动启动一个新的日志文件。

foramt-riqi和格式，时间是在这里：

(define (format-riqi the_date) 
    (format "~a~a~a" 
      (date-year the_date) 
      (~a (date-month the_date) #:min-width 2 #:pad-string "0" #:align 'right) 
      (~a (number->string (date-day the_date)) #:min-width 2 #:pad-string "0" #:align 'right))) 

(define (format-time the_date) 
    (format "~a:~a:~a" 
      (~a (date-hour the_date) #:min-width 2 #:pad-string "0" #:align 'right) 
      (~a (date-minute the_date) #:min-width 2 #:pad-string "0" #:align 'right) 
      (~a (date-second the_date) #:min-width 2 #:pad-string "0" #:align 'right)))