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file-length

file-length Function

Syntax:

file-length stream → length

Arguments and Values:

stream—a stream associated with a file.

length—a non-negative integer or nil.

Description:

file-length returns the length of stream, or nil if the length cannot be determined.

For a binary file, the length is measured in units of the element type of the stream.

Examples:

(with-open-file (s "decimal-digits.text" 
		   
		   
		   :direction :output :if-exists :error) 
  (princ "0123456789" s) 
  (truename s)) 
→ #P"A:>Joe>decimal-digits.text.1" 
(with-open-file (s "decimal-digits.text") 
  (file-length s)) 
→ 10

Exceptional Situations:

Should signal an error of type type-error if stream is not a stream associated with a file.

See Also:

open

Expanded Reference: file-length​

Basic Usage​

file-length returns the length of the file associated with a stream, or NIL if the length cannot be determined.

(with-open-file (s "/tmp/cl-fl-test.txt"
                   :direction :output :if-exists :supersede)
  (write-string "0123456789" s))

(with-open-file (s "/tmp/cl-fl-test.txt")
  (file-length s))
=> 10

Binary File Length​

For binary files, the length is measured in units of the element type.

(with-open-file (s "/tmp/cl-fl-test.bin"
                   :direction :output
                   :element-type '(unsigned-byte 8)
                   :if-exists :supersede)
  (dotimes (i 5) (write-byte i s)))

(with-open-file (s "/tmp/cl-fl-test.bin"
                   :element-type '(unsigned-byte 8))
  (file-length s))
=> 5

Using with file-position​

file-length and file-position together enable random access patterns.

(with-open-file (s "/tmp/cl-fl-test.bin"
                   :element-type '(unsigned-byte 8))
  (let ((len (file-length s)))
    (file-position s (1- len))    ; seek to last byte
    (read-byte s)))
=> 4