Nrthugu

I am reading stdin in a loop and do some comparaison with a bunch of "if" to decide what to do according to the input.

Here is a shortened snippet of the code :

CHARACTER (len= :), allocatable :: input

CHARACTER (len=4096) :: inbuffer            ! frustrating but... well, fortran :3



DO



    ! get input

    READ(*, '(a)') inbuffer     ! because apparently you can't have allocation on read so you can't just read "input". meh.

    input = TRIM(inbuffer)

    CALL debug_log(input)



    IF(input .EQ. 'uci') THEN

        CALL debug_log("   printing uci info")



    !isready

    ELSE IF(input .EQ. 'isready') THEN

        CALL debug_log("   isready -> readyok")

        WRITE(*, '(a)') "readyok"



    !ucinewgame

    ELSE IF(input .EQ. 'ucinewgame') THEN

        CALL debug_log("not implemented : reset board and start a new game")



    !position

    ELSE IF(input(1:8) .EQ. 'position') THEN

        CALL debug_log("not implemented : set position")



    !quit -> exit main loop

    ELSE IF(input .EQ. 'quit') THEN

        CALL debug_log("   quit command issued, exiting main loop")

        EXIT



    !non uci command

        !nothing yet



    !unknown command

    ELSE

        CALL debug_log("   ignoring invalid command")

    END IF



end do

The input will expect command like "position 123 23415 etc..."

If I type "posi" it's say it's an invalid command as expected.

If I type "position" it say it's not implemented as expected too.

However:

• If I type "position": I get not implemented


• Followed by "posi": it says "not implemented" instead of "invalid command"

My guess is that it read 8 character even if the input is only 4 and since the previous command was "position" it make posi + tion = position

Here is some log to demonstrate:

** opening debug file : 20181111 / 223418.127

223418.127 : Initializing Fortiche engine

223418.129 : Entering main loop

223420.859 : posi

223420.859 :    ignoring invalid command

223426.467 : xxxxtion

223426.467 :    ignoring invalid command

223430.498 : posi

223430.498 : not implemented : set position

223437.323 : xxxxxxxxx

223437.323 :    ignoring invalid command

223439.418 : posi

223439.418 :    ignoring invalid command

223443.979 : position

223443.979 : not implemented : set position

223447.122 : quit

223447.122 :    quit command issued, exiting main loop

223447.122 : closing, bye

xxxxtion + posi = position

Which is clearly wrong but I can understand how it ended up like this.

Should I use something other than .EQ.?
When I print the input it clearly doesn't print the input + whatever garbage was left behind in memory. But it's doing it when comparing string of possibly different length.

What can I do to solve this problem?

I'm not even started with the hardcore parsing and I already have a problem.

I'm using GNU Fortran on Windows.

Yes, it's UCI stuff as Universal Chess Interface.

EDIT : Full source code : https://github.com/ker2x/fortiche (comment the dirty hack at line 107 & 108 to reproduce the problem)

Substring references need to have starting and ending positions that are within the limits of the string.

You don't defend against a string that has a length less than eight prior to the substring reference input(1:8) .eq. 'position'.

With input shorter than eight characters, your program is non-conforming, anything can then happen, where anything very reasonably includes the behaviour you see.

Runtime debugging options may help to catch this programming error, depending on the capabilities of your compiler.