Making Xerces parse a string instead of a file

Question

I know how to create a complete dom from an xml file just using XercesDOMParser:

xercesc::XercesDOMParser parser = new xercesc::XercesDOMParser();
parser->parse(path_to_my_file);
parser->getDocument(); // From here on I can access all nodes and do whatever i want

Well, that works... but what if I'd want to parse a string? Something like

std::string myxml = "<root>...</root>";
xercesc::XercesDOMParser parser = new xercesc::XercesDOMParser();
parser->parse(myxml);
parser->getDocument(); // From here on I can access all nodes and do whatever i want

I'm using version 3. Looking inside the AbstractDOMParser I see that parse method and its overloaded versions, only parse files.

How can I parse from a string?

Solution 1

Create a MemBufInputSource and parse that:

xercesc::MemBufInputSource myxml_buf(myxml.c_str(), myxml.size(),
                                     "myxml (in memory)");
parser->parse(myxml_buf);

Solution 2

Use the following overload of XercesDOMParser::parse():

void XercesDOMParser::parse(const InputSource& source);

passing it a MemBufInputSource:

MemBufInputSource src((const XMLByte*)myxml.c_str(), myxml.length(), "dummy", false);
parser->parse(src);

Solution 3

Im doing it another way. If this is incorrect, please tell me why. It seems to work. This is what parse expects:

DOMDocument* DOMLSParser::parse(const DOMLSInput * source )

So you need to put in a DOMLSInput instead of a an InputSource:

xercesc::DOMImplementation * impl = xercesc::DOMImplementation::getImplementation();
xercesc::DOMLSParser *parser = (xercesc::DOMImplementationLS*)impl)->createLSParser(xercesc::DOMImplementation::MODE_SYNCHRONOUS, 0);
xercesc::DOMDocument *doc;

xercesc::Wrapper4InputSource source (new xercesc::MemBufInputSource((const XMLByte *) (myxml.c_str()), myxml.size(), "A name");
parser->parse(&source);

Comments

[Fred Foo]

It's a "fake system id" that's used in error messages and "any entities which are referred to from this entity via relative paths/URLs will be relative to this fake system id". See API docs.

[Andry]

larsmans could you please tell me why, when using your code and correctly printing the xml, when I call Terminate() my app goes on Segmentation Fault?????

[Fred Foo]

@Andry, I can't tell with just this info. Can you try copying the string with new char[] and setting the 4th (adoptBuffer) ctor argument to true? (see xerces.apache.org/xerces-c/apiDocs-3/…)

[Andry]

Well I discovered it... see here... absurd ahaha xerces.apache.org/xerces-c/faq-parse-2.html#faq-7

[Fred Foo]

@Andry: I know, the Xerces rules for memory allocation are overly complicated. They seem never to have heard of RAII. Too bad.

[Silver]

How can I figure out in what namespace MemBufInputSource and Wrapper4InputSource are in? I'm having serious trouble with namespaces in xerces. Ty

[Jesse Chisholm]

@Andry - sadly, the absurd ahaha link has aged into oblivion. :( Appears to have become: xerces.apache.org/xerces-c/faq-parse-3.html#faq-7

[Mike S]

How did you solve the seg fault? I'm having the same problem.

[villasv]

It's on xercesc namespace, but you also need #include <xercesc/framework/MemBufInputSource.hpp> . I'm two years late, but I had the same issue and someone else can have it again later.

[villasv]

Also +1 for also specifying the necessary cast.

[user23573]

Thanks for hinting this. This answer seems to be closer to the actual DOM Programming Guide

[steiryx]

I tried to use this but it seems to fail, when i tried to replace double quotes to single and add \n\ on each line, parsing seems ok. I did that based on MemParse.cpp sample in xerces. Do you know the problem with that?

[Silver]

Hi, This is an answer from 7 year ago so I have no clue what I was doing at the time. Maybe if you can elaborate I can think with you. Where/what line did you change the quotes and add the \n?

[chars]

Don't know if this is why any of above comments were seeing seg faults but MemBufInputSource doesn't seem to work unless you first initialize the system. More detail in answer below.