GetAsyncChar()

Description

GetAsyncChar() is used to retrieve a single character of input from the user.

Call Signature

string GetAsyncChar ( )

Return Value

string

A string of length zero or one, is returned depending on whether a character of pending input was found. See Remarks section.

Remarks

This intrinsic function will return either a single character of input from the user if the user has hit a key, or an empty string if there is no pending input. Unlike the INPUT command, this can be used to get input from the user asynchronously. That is to say, the procedure can check for input without blocking while waiting for it.

The GetAsyncChar() call puts the terminal in a special asynchronous input mode on some systems. Therefore it is critical that AsyncDisable() be called before either terminating a script, attempting to use the INPUT command, or calling a subprocedure or subprogram that attempts to get conventional input from the user.

Example

The following example script will loop waiting for input from the user. Each character is printed out as an ascii value and as a string. When the `q' key is returned, the script terminates, disabling asynchronous input mode. Also note that the script sleeps for a short time when it doesn't get any input in order to avoid "busy waiting" and while waiting for input.

 local int     bDone
 local string  response

 while( bDone = 0 )
    response = GetAsyncChar()

    if( f$len(response) = 0 )then
        call Sleep( 0.1 )
    else
        printf "%d {%s}\n", f$ascii(response[1]), response
        if( response = "q" )then
            bDone = 1
        endifg
    endif
 endwhile

 call AsyncDisable()