Lisp Function fails, although working previously (Draft Sight, SVG to CAD)

Question

We are trying to implement a Draft Sight/AutoCad script that will transform a SVG file into a CAD drawing.

The principal idea is to read the file line by line (performed by ReadSVGData), split the svg definitions by spaces (ReadHTMLItemData), read the individual HTML attributes into a list and based on the type of the SVG item draw a CAD element. So much in regards to the principal...

The unususal part is, that whenever the Html Attributes, like "id="Box_8_0"" are sent to the findchar function, by attrlis function, the script fails, although the same arrangement went well before

Does anybody have a hint where my mistake is hidden?

(defun findchar (FindChar Text) 

    (setq
        ;current location in string
        coord 1
        ;Init Return Coordinate
        ReturnCoord 0
        ;Length of Searched Item, to enable string searching
        FindCharLen (strlen FindChar)
        ;Nil Count: Requires as regular expressions like (/t) are identified as two times ascii char 9
        NilCnt 0
        ;Storage of last Char Ascii to identify regular expressions
        LastCharAsci -1
    )

    ;iterate the String and break in case of the first occurence
    (while (and (<= coord (strlen Text) ) (= ReturnCoord 0))
        ;Current Character
        (setq CurChar (substr Text coord FindCharLen))

        ;Find Searched String
        (if (= FindChar CurChar)
            (setq ReturnCoord coord)
        )

        ;Check for regular expression
        (if (and (= LastCharAsci 9) (= (ascii CurChar) 9))
            (setq NilCnt (+ NilCnt 1))
        )

        ;Update String position and String
        (setq LastCharAsci (ascii CurChar))
        (setq coord (+ coord 1))
    )
    ;return variable
    (- ReturnCoord NilCnt)
)


(defun attrlis (HTMLAttr)
    (setq Koordi 0)




    (progn
        (setq CharLoc (findchar "<" HTMLAttr))

        (princ HTMLAttr)
        (terpri)
    )

    (+ Koordi 1)
)

(defun ReadHTMLItemData(HTMLItem)

    (setq 
        coord 1
        HTMLItmBgn 1
        Attributes 0
        CurChar 0
        Dictionary 0

    )

    ;(princ HTMLItem)
    ;(terpri)
    (while (<= coord (strlen HTMLItem))

        (setq CurChar (substr HTMLItem coord 1))
        (if (or (= (ascii CurChar) 32) (= (ascii CurChar) 62))
            (progn
                (if (> (- coord HTMLItmBgn) 0)
                    (progn
                        (setq htmlattr (substr HTMLItem HTMLItmBgn (- coord HTMLItmBgn)))

                        (setq Result (attrlis htmlattr))

                        (princ Result)

                        (setq HTMLItmBgn (+ coord 1))
                    )
                )
            )
        )
        (setq coord (+ coord 1))
    )
)


(defun ReadLineContents(Line)
    (if (/= Line nil)
        (progn
            ;(princ Line)
            ;(terpri)

            (setq 

                Bgn (findchar "<" Line)
                End (findchar ">" Line)
                ItemDef (substr Line (+ Bgn (strlen "<"))  End)
            )

            (ReadHTMLItemData ItemDef)
        )
    )
)



(defun C:ReadSVGData()
    (setq SVGFile (open (getfiled "Select a file" "" "svg" 0) "r"))

    (setq Line 1)
    (while (/= Line nil)

        (setq Line (read-line SVGFile))
        (ReadLineContents Line)
    )

    (close SVGFile)

    (princ "Done")
)

Reading the following file:

<svg class="boxview" id="boxview" style="width:1198.56px; height:486.8004px; display:block;" viewBox="0 0 1198.56 486.8004">
<g id="BD_box">
    <rect class="box" id="Box_8_0" x="109.21" y="394.119" width="58.512" height="62.184" box="4047"></rect>
</g>
</svg>

EDIT

Change of substring Index, based on satraj's answer

Answer 1

The problem lies in the way the "substr" Autolisp function is used. The start index of substr always starts from index 1 (not from 0). So your code must be changed such that the start index are initialized as 1. The following lines in your code fails.

(setq CurChar (substr HTMLItem coord 1))

(setq htmlattr (substr HTMLItem HTMLItmBgn (- coord HTMLItmBgn)))

Since coord and HTMLItemBgn variables are initialized as 0, the substr function fails.

Also, why not use "vl-string-search" function if you want to find the position of a text in a string? you can get rid of the findchar function.

An Example:

(setq CharLoc (vl-string-search "<" HTMLAttr))

In general, if you want to debug failures in AutoLisp, add the following function to your lisp file and it will print a stack trace in case of failures, which will enable you to locate exact place where the error occured.

(defun *error* (msg)
(vl-bt)
)