read-char (AutoLISP)

Returns the integer representing the character read from the keyboard input buffer or from an open file

Supported Platforms: Windows and Mac OS

Signature

(read-char [file-desc])

file-desc

Type: File

A file descriptor (obtained from open) referring to an open file. If no file-desc is specified, read-char obtains input from the keyboard input buffer.

Return Values

Type: Integer

Character code in the range of 1-65536.

The read-char function returns a single newline character (code 10) whenever it detects an end-of-line character or character sequence.

Release Information

Releases:

• AutoCAD R12 and later on Windows
• AutoCAD 2011 and later on Mac OS

History

AutoCAD 2021

• Return value was modified to support Unicode characters and might be different than earlier releases. For example, suppose the "€" character was in a file named test.txt. Previously, the value of this character would be returned as ASCII code 128, but with Unicode support the value of this character would be returned as Unicode code 8364.

  (setq fp (open "E:\\test.txt" "r" "utf8"))
  (read-char fp)
  8364

• LISPSYS system variable controls which AutoLISP engine is used and the behavior of the function.
  • 0 - ASCII character support (legacy behavior)
  • 1 or 2 - Unicode character support
  Note: After the value of the LISPSYS system variable has been changed, AutoCAD must be restarted for the change to take affect.

Examples

The following example omits file-desc, so read-char looks for data in the keyboard buffer:

(read-char)

The keyboard buffer is empty, so read-char waits for user input:

ABC
65

The user entered ABC; read-char returned the code representing the first character entered (A). The next three calls to read-char return the data remaining in the keyboard input buffer. This data translates to 66 (the code for the letter B), 67 (C), and 10 (newline), respectively:

(read-char)
66

(read-char)
67

(read-char)
10

With the keyboard input buffer now empty, read-char waits for user input the next time it is called:

(read-char)