304 lines
5.8 KiB
HTML
304 lines
5.8 KiB
HTML
<HTML
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>How to use a backtrace</TITLE
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TITLE="How to print something to debug log file"
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>Caudium HOWTO</TH
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>Chapter 6. Developing with Caudium</TD
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><A
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NAME="backtrace">6.5. How to use a backtrace</H1
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><P
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> A backtrace is text that will show you where your program come before the
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error. This is very useful for developers when they debug.
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The best is to take an example. Did you try the who module at the end of <A
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HREF="firstmodule.html"
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>Section 6.4</A
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>?
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If so take it and check it works. Now change the line
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<TT
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CLASS="computeroutput"
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>string command = QUERY(path2who)+" "+QUERY(options2who);</TT
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> to <TT
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CLASS="computeroutput"
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>string command = 0;</TT
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>.
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This will create an error because we put an int into a string. If we want to
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do that, we have to cast it (for example, use (string) 0).
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If you have not done it yet, press the <TT
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CLASS="option"
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>More options</TT
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> button in the <SPAN
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CLASS="abbrev"
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>CIF.</SPAN
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> and
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reload the module. Check that the <TT
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CLASS="option"
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>Global Variables</TT
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> -> <TT
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CLASS="option"
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>show_internals</TT
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> option
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is set to yes, and try your module. You will have an error which should look like this:
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</P
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><DIV
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CLASS="informalexample"
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><A
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NAME="AEN1017"><P
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></P
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><TABLE
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><TR
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><TD
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><FONT
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COLOR="#000000"
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><PRE
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CLASS="programlisting"
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> Caudium version: Caudium (Caudium/1.2.0)
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Requested URL: /who
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Error: Sprintf: Wrong type for argument 2: expected string, got int.
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../local/modules/who.pike:76:
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CaudiumModule(Who,My first virtual server)->find_file("",object)
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base_server/configuration.pike (version 1.91):1587:
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Configuration(My first virtual server)->low_get_file(object,0)
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base_server/configuration.pike (version 1.91):1779:
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Configuration(My first virtual server)->get_file(object,0)
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base_server/configuration.pike (version 1.91):1760:
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Configuration(My first virtual server)->handle_request(object)
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protocols/http.pike (version 1.71):1549: unknown function()
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protocols/http.pike (version 1.71):1610:
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unknown function(0,"GET /who HTTP/1.1\r\nHost: localhost\r\nUser-Agent:
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Mozilla/5.0 (X11; U; Linux i686; en-US; rv:0.9.8)
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Gecko/20020214\r\nAccept: text/xml,application/xml,
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application/xhtml+xml,text/html;q=0.9,text/plain"+[246])
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/usr/local/pike/7.2.262/lib/modules/Stdio.pmod/module.pmod
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(version 1.114):683:
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Stdio.File("socket", "127.0.0.1 1260", 777 /* fd=-1 */)
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->__stdio_read_callback()
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</PRE
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></FONT
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></TD
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></TR
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></TABLE
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><P
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></P
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></DIV
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><P
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> This seems awful but it is not. The first line is the error in itself:
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<DIV
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CLASS="informalexample"
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><A
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NAME="AEN1020"><P
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></P
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><TABLE
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BORDER="0"
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BGCOLOR="#E0E0E0"
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WIDTH="100%"
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><TR
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><TD
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><FONT
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COLOR="#000000"
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><PRE
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CLASS="programlisting"
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> "Error: Sprintf: Wrong type for argument 2: expected string, got int."
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The next line "../local/modules/who.pike:76:
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CaudiumModule(Who,My first virtual server)->find_file("",object)"
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is the program (../local/modules/who.pike at line 76)
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</PRE
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></FONT
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></TD
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></TR
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></TABLE
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><P
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></P
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></DIV
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>
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where the error occurred. <TT
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CLASS="function"
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>find_file</TT
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> is the name of the function where the
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error occurred and you have also the arguments given to it.
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If you use the source, you see mixed find_file(string path, object id). So
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here path="" and id=object <A
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NAME="AEN1023"
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HREF="#FTN.AEN1023"
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>[1]</A
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>.
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Next line is the function (<TT
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CLASS="function"
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>low_get_file</TT
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> in <TT
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CLASS="filename"
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>configuration.pike</TT
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>) that has
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called <TT
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CLASS="function"
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>find_file</TT
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> in <TT
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CLASS="filename"
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>who.pike</TT
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>. You also have its arguments and so on.
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This backtrace is very useful when the error doesn't come directly
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from your code but from another code before.
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</P
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></DIV
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><H3
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CLASS="FOOTNOTES"
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>Notes</H3
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VALIGN="TOP"
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WIDTH="5%"
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><A
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NAME="FTN.AEN1023"
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HREF="backtrace.html#AEN1023"
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>[1]</A
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></TD
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ALIGN="LEFT"
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VALIGN="TOP"
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WIDTH="95%"
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><P
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>Pike can't display contents of an object but can display any other types.</P
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></TD
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></TR
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