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libxml2 with C++ exception

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  libxml2 with C++ exception Philipp Kraus <philipp.kraus@flashpixx.de> - 2011-07-13 13:34 +0200
    Re: libxml2 with C++ exception Michael DOUBEZ <michael.doubez@free.fr> - 2011-07-13 05:25 -0700
      Re: libxml2 with C++ exception Philipp Kraus <philipp.kraus@flashpixx.de> - 2011-07-13 15:14 +0200

#7777 — libxml2 with C++ exception

Hello,

I' using for XML parsing the libxml2 library and I use the native C 
interface (not the C++ bindings). I parse a std::string with this code
        const char* l_xmlcontent = p_xml.c_str();
        xmlDocPtr l_xml          = xmlParseMemory( l_xmlcontent, 
strlen(l_xmlcontent) );

p_xml is a std::string. In some cases the XML data within the string 
can't be valid and I get the correct message:
Entity: line 1: parser error : Start tag expected, '<' not found

The message is shown on the command line on each time, but I would like 
to catch the error and would like to throw an exception. A try-catch 
statement around the xmlParseMemory does not work. I've found some 
notes that I can use a callback function, which is run on an error, but 
I don't find any information for the implementation.

I hope my question isn't off-topic and anyonw can help me to create on 
a parser error a correct exception

Thanks

Phil
 

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#7779

On Jul 13, 1:34 pm, Philipp Kraus <philipp.kr...@flashpixx.de> wrote:
> I' using for XML parsing the libxml2 library and I use the native C
> interface (not the C++ bindings). I parse a std::string with this code
>         const char* l_xmlcontent = p_xml.c_str();
>         xmlDocPtr l_xml          = xmlParseMemory( l_xmlcontent,
> strlen(l_xmlcontent) );
>
> p_xml is a std::string. In some cases the XML data within the string
> can't be valid and I get the correct message:
> Entity: line 1: parser error : Start tag expected, '<' not found
>
> The message is shown on the command line on each time, but I would like
> to catch the error and would like to throw an exception.

Catching the error is easy: libxml2 let you define the error handlers:
see the xml*ErrorFunc() functions in the API.

> A try-catch
> statement around the xmlParseMemory does not work. I've found some
> notes that I can use a callback function, which is run on an error, but
> I don't find any information for the implementation.

*BUT* propagating an exception through C code is a bad idea. The
libxml2 doesn't expect to loose flow for control and leaks are likely
to occur. The proper solution is to build a C++ wrapper that stores
errors and throw them upon error return code (you can use
xmlCtxtGetLastError/xmlGetLastError)

--
Michael

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#7780

On 2011-07-13 14:25:17 +0200, Michael DOUBEZ said:

> On Jul 13, 1:34 pm, Philipp Kraus <philipp.kr...@flashpixx.de> wrote:
>> I' using for XML parsing the libxml2 library and I use the native C
>> interface (not the C++ bindings). I parse a std::string with this code
>>         const char* l_xmlcontent = p_xml.c_str();
>>         xmlDocPtr l_xml          = xmlParseMemory( l_xmlcontent,
>> strlen(l_xmlcontent) );
>> 
>> p_xml is a std::string. In some cases the XML data within the string
>> can't be valid and I get the correct message:
>> Entity: line 1: parser error : Start tag expected, '<' not found
>> 
>> The message is shown on the command line on each time, but I would like
>> to catch the error and would like to throw an exception.
> 
> Catching the error is easy: libxml2 let you define the error handlers:
> see the xml*ErrorFunc() functions in the API.

oh thanks a lot :-P

> 
>> A try-catch
>> statement around the xmlParseMemory does not work. I've found some
>> notes that I can use a callback function, which is run on an error, but
>> I don't find any information for the implementation.
> 
> *BUT* propagating an exception through C code is a bad idea. The
> libxml2 doesn't expect to loose flow for control and leaks are likely
> to occur. The proper solution is to build a C++ wrapper that stores
> errors and throw them upon error return code (you can use
> xmlCtxtGetLastError/xmlGetLastError)

I do this for a special XML structure. Parsing XML, checking errors, 
clearing all data and throwing an error if needed.

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