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Posted to c-users@xerces.apache.org by "Galande, Manish" <Ma...@bmc.com> on 2009/10/08 15:11:31 UTC

Reading portions of XML file.

Hi,

I want to read the portions of XML file depending on byte-position, using getSrcOffset(). Is there a way I can directly start reading/parsing from a pre-defined offset in the source, similar to lseek and read?

Thanks.

Manish

RE: Reading portions of XML file.

Posted by John Lilley <jl...@datalever.com>.
My suggestion is to make your class "fake" a root tag, which it prepends to the actual data.  Here bytesRead is a counter you keep in your class:

XMLSize_t MyFileInputStream::readBytes(XMLByte* const toFill, const XMLSize_t maxToRead) {
	if (bytesRead == 0) {
		fseek(...fp...);	// skip front of file
	}
	int bytesReturned = 0;
	if (bytesRead < 6) {
		int bytesToCopy = min(maxToRead, 6-bytesRead);
		memcpy(toFill, "<root>", bytesToCopy);
		bytesRead += bytesToCopy;
		maxToRead -= bytesToCopy;
		toFile += bytesToCopy;
		bytesReturned += bytesToCopy;
	}
	// normal file I/O
	bytesReturned += fread(toFill, 1, maxToRead, fp);
	return bytesReturned;
}

The other issue you will have is that the SAX parser is not a state machine.  It won't return from parsing and let you pick up later where it left off.  There are two ways of dealing with this that I can think of.  The simpler is to just make a new parser and fake a new root tag every time you see more input.  The harder is to make your file reader run in a separate thread, and communicate to your inputsource object in the foreground thread that more data is available via a semaphore or other thread-synchronization primitive.  It depends on the requirements of your processing model.

john


-----Original Message-----
From: Galande, Manish [mailto:Manish_Galande@bmc.com] 
Sent: Thursday, October 22, 2009 1:28 AM
To: c-users@xerces.apache.org
Subject: RE: Reading portions of XML file.

I'm able to reposition the file pointer and start reading from there on. But now the problem is I can read only one tag at a time. The first tag encountered, during read, is treated as root tag and startDocument/endDocument events are generated accordingly. Where as I want to continue reading. Here is a sample xml file:
<root>
<rec>rec1</rec>
<rec>rec2</rec>
<rec>rec3</rec>
</root>

Initially the file contains only two lines and later lines are added at a regular interval. My intent is to parse whatever the content of the file and then do not parse the same content again next time I read the file.
The approach that I'm thinking of is to read till the root-tag in xml file and then reposition the file-pointer and start reading from there on. But, I'm not sure if this can be done. Is there any way to do this?

Thanks.

Manish

-----Original Message-----
From: Galande, Manish
Sent: Friday, October 09, 2009 6:58 PM
To: 'c-users@xerces.apache.org'
Subject: RE: Reading portions of XML file.

True. I realized it after I sent the earlier reply. Till then I was thinking only of Xerces API's but it too implements the platform dependent code using these native calls.

Manish

-----Original Message-----
From: John Lilley [mailto:jlilley@datalever.com]
Sent: Friday, October 09, 2009 6:33 PM
To: c-users@xerces.apache.org
Subject: RE: Reading portions of XML file.

You have to implement that in your class.  Presumably your class will contain a file handle or object.  Call fseek() or lseek() as appropriate.
john

-----Original Message-----
From: Galande, Manish [mailto:Manish_Galande@bmc.com]
Sent: Friday, October 09, 2009 5:52 AM
To: c-users@xerces.apache.org
Subject: RE: Reading portions of XML file.

Thanks John.
But how would I move to the interested offset when I already have the offset. I'm not aware of any lseek like call in Xerces.

Manish

-----Original Message-----
From: John Lilley [mailto:jlilley@datalever.com]
Sent: Thursday, October 08, 2009 7:04 PM
To: c-users@xerces.apache.org
Subject: RE: Reading portions of XML file.

Er, a bit cleaner snippet:

You can subclass InputSource and InputStream, then implement it however you like.  In this snippet, XN:: is defined as the Xerces namespace.

class MyFileInputStream : public XN::BinInputStream {
public:
        MyFileInputStream(...) {}
        virtual XMLFilePos curPos() const { return ... }
        virtual XMLSize_t readBytes(XMLByte* const toFill, const XMLSize_t maxToRead) {
                return ...;
        }
        // No "out-of-band" content type
        virtual const XMLCh* getContentType() const { return 0; }
private:
        ...
};
class MyFileInputSource : public XN::InputSource
{
public :
        MyFileInputSource(...) {}
        virtual XN::BinInputStream* makeStream() const {
                // Caller is owner of stream
                return new MyFileInputStream(...);
        }
private:
        ...
};

john

-----Original Message-----
From: Galande, Manish [mailto:Manish_Galande@bmc.com]
Sent: Thursday, October 08, 2009 7:12 AM
To: c-users@xerces.apache.org
Subject: Reading portions of XML file.

Hi,

I want to read the portions of XML file depending on byte-position, using getSrcOffset(). Is there a way I can directly start reading/parsing from a pre-defined offset in the source, similar to lseek and read?

Thanks.

Manish

RE: Reading portions of XML file.

Posted by "Galande, Manish" <Ma...@bmc.com>.
I'm able to reposition the file pointer and start reading from there on. But now the problem is I can read only one tag at a time. The first tag encountered, during read, is treated as root tag and startDocument/endDocument events are generated accordingly. Where as I want to continue reading. Here is a sample xml file:
<root>
<rec>rec1</rec>
<rec>rec2</rec>
<rec>rec3</rec>
</root>

Initially the file contains only two lines and later lines are added at a regular interval. My intent is to parse whatever the content of the file and then do not parse the same content again next time I read the file.
The approach that I'm thinking of is to read till the root-tag in xml file and then reposition the file-pointer and start reading from there on. But, I'm not sure if this can be done. Is there any way to do this?

Thanks.

Manish

-----Original Message-----
From: Galande, Manish
Sent: Friday, October 09, 2009 6:58 PM
To: 'c-users@xerces.apache.org'
Subject: RE: Reading portions of XML file.

True. I realized it after I sent the earlier reply. Till then I was thinking only of Xerces API's but it too implements the platform dependent code using these native calls.

Manish

-----Original Message-----
From: John Lilley [mailto:jlilley@datalever.com]
Sent: Friday, October 09, 2009 6:33 PM
To: c-users@xerces.apache.org
Subject: RE: Reading portions of XML file.

You have to implement that in your class.  Presumably your class will contain a file handle or object.  Call fseek() or lseek() as appropriate.
john

-----Original Message-----
From: Galande, Manish [mailto:Manish_Galande@bmc.com]
Sent: Friday, October 09, 2009 5:52 AM
To: c-users@xerces.apache.org
Subject: RE: Reading portions of XML file.

Thanks John.
But how would I move to the interested offset when I already have the offset. I'm not aware of any lseek like call in Xerces.

Manish

-----Original Message-----
From: John Lilley [mailto:jlilley@datalever.com]
Sent: Thursday, October 08, 2009 7:04 PM
To: c-users@xerces.apache.org
Subject: RE: Reading portions of XML file.

Er, a bit cleaner snippet:

You can subclass InputSource and InputStream, then implement it however you like.  In this snippet, XN:: is defined as the Xerces namespace.

class MyFileInputStream : public XN::BinInputStream {
public:
        MyFileInputStream(...) {}
        virtual XMLFilePos curPos() const { return ... }
        virtual XMLSize_t readBytes(XMLByte* const toFill, const XMLSize_t maxToRead) {
                return ...;
        }
        // No "out-of-band" content type
        virtual const XMLCh* getContentType() const { return 0; }
private:
        ...
};
class MyFileInputSource : public XN::InputSource
{
public :
        MyFileInputSource(...) {}
        virtual XN::BinInputStream* makeStream() const {
                // Caller is owner of stream
                return new MyFileInputStream(...);
        }
private:
        ...
};

john

-----Original Message-----
From: Galande, Manish [mailto:Manish_Galande@bmc.com]
Sent: Thursday, October 08, 2009 7:12 AM
To: c-users@xerces.apache.org
Subject: Reading portions of XML file.

Hi,

I want to read the portions of XML file depending on byte-position, using getSrcOffset(). Is there a way I can directly start reading/parsing from a pre-defined offset in the source, similar to lseek and read?

Thanks.

Manish

RE: Reading portions of XML file.

Posted by "Galande, Manish" <Ma...@bmc.com>.
True. I realized it after I sent the earlier reply. Till then I was thinking only of Xerces API's but it too implements the platform dependent code using these native calls.

Manish

-----Original Message-----
From: John Lilley [mailto:jlilley@datalever.com]
Sent: Friday, October 09, 2009 6:33 PM
To: c-users@xerces.apache.org
Subject: RE: Reading portions of XML file.

You have to implement that in your class.  Presumably your class will contain a file handle or object.  Call fseek() or lseek() as appropriate.
john

-----Original Message-----
From: Galande, Manish [mailto:Manish_Galande@bmc.com]
Sent: Friday, October 09, 2009 5:52 AM
To: c-users@xerces.apache.org
Subject: RE: Reading portions of XML file.

Thanks John.
But how would I move to the interested offset when I already have the offset. I'm not aware of any lseek like call in Xerces.

Manish

-----Original Message-----
From: John Lilley [mailto:jlilley@datalever.com]
Sent: Thursday, October 08, 2009 7:04 PM
To: c-users@xerces.apache.org
Subject: RE: Reading portions of XML file.

Er, a bit cleaner snippet:

You can subclass InputSource and InputStream, then implement it however you like.  In this snippet, XN:: is defined as the Xerces namespace.

class MyFileInputStream : public XN::BinInputStream {
public:
        MyFileInputStream(...) {}
        virtual XMLFilePos curPos() const { return ... }
        virtual XMLSize_t readBytes(XMLByte* const toFill, const XMLSize_t maxToRead) {
                return ...;
        }
        // No "out-of-band" content type
        virtual const XMLCh* getContentType() const { return 0; }
private:
        ...
};
class MyFileInputSource : public XN::InputSource
{
public :
        MyFileInputSource(...) {}
        virtual XN::BinInputStream* makeStream() const {
                // Caller is owner of stream
                return new MyFileInputStream(...);
        }
private:
        ...
};

john

-----Original Message-----
From: Galande, Manish [mailto:Manish_Galande@bmc.com]
Sent: Thursday, October 08, 2009 7:12 AM
To: c-users@xerces.apache.org
Subject: Reading portions of XML file.

Hi,

I want to read the portions of XML file depending on byte-position, using getSrcOffset(). Is there a way I can directly start reading/parsing from a pre-defined offset in the source, similar to lseek and read?

Thanks.

Manish

RE: Reading portions of XML file.

Posted by John Lilley <jl...@datalever.com>.
You have to implement that in your class.  Presumably your class will contain a file handle or object.  Call fseek() or lseek() as appropriate.
john

-----Original Message-----
From: Galande, Manish [mailto:Manish_Galande@bmc.com] 
Sent: Friday, October 09, 2009 5:52 AM
To: c-users@xerces.apache.org
Subject: RE: Reading portions of XML file.

Thanks John.
But how would I move to the interested offset when I already have the offset. I'm not aware of any lseek like call in Xerces.

Manish

-----Original Message-----
From: John Lilley [mailto:jlilley@datalever.com]
Sent: Thursday, October 08, 2009 7:04 PM
To: c-users@xerces.apache.org
Subject: RE: Reading portions of XML file.

Er, a bit cleaner snippet:

You can subclass InputSource and InputStream, then implement it however you like.  In this snippet, XN:: is defined as the Xerces namespace.

class MyFileInputStream : public XN::BinInputStream {
public:
        MyFileInputStream(...) {}
        virtual XMLFilePos curPos() const { return ... }
        virtual XMLSize_t readBytes(XMLByte* const toFill, const XMLSize_t maxToRead) {
                return ...;
        }
        // No "out-of-band" content type
        virtual const XMLCh* getContentType() const { return 0; }
private:
        ...
};
class MyFileInputSource : public XN::InputSource
{
public :
        MyFileInputSource(...) {}
        virtual XN::BinInputStream* makeStream() const {
                // Caller is owner of stream
                return new MyFileInputStream(...);
        }
private:
        ...
};

john

-----Original Message-----
From: Galande, Manish [mailto:Manish_Galande@bmc.com]
Sent: Thursday, October 08, 2009 7:12 AM
To: c-users@xerces.apache.org
Subject: Reading portions of XML file.

Hi,

I want to read the portions of XML file depending on byte-position, using getSrcOffset(). Is there a way I can directly start reading/parsing from a pre-defined offset in the source, similar to lseek and read?

Thanks.

Manish

RE: Reading portions of XML file.

Posted by "Galande, Manish" <Ma...@bmc.com>.
Thanks John.
But how would I move to the interested offset when I already have the offset. I'm not aware of any lseek like call in Xerces.

Manish

-----Original Message-----
From: John Lilley [mailto:jlilley@datalever.com]
Sent: Thursday, October 08, 2009 7:04 PM
To: c-users@xerces.apache.org
Subject: RE: Reading portions of XML file.

Er, a bit cleaner snippet:

You can subclass InputSource and InputStream, then implement it however you like.  In this snippet, XN:: is defined as the Xerces namespace.

class MyFileInputStream : public XN::BinInputStream {
public:
        MyFileInputStream(...) {}
        virtual XMLFilePos curPos() const { return ... }
        virtual XMLSize_t readBytes(XMLByte* const toFill, const XMLSize_t maxToRead) {
                return ...;
        }
        // No "out-of-band" content type
        virtual const XMLCh* getContentType() const { return 0; }
private:
        ...
};
class MyFileInputSource : public XN::InputSource
{
public :
        MyFileInputSource(...) {}
        virtual XN::BinInputStream* makeStream() const {
                // Caller is owner of stream
                return new MyFileInputStream(...);
        }
private:
        ...
};

john

-----Original Message-----
From: Galande, Manish [mailto:Manish_Galande@bmc.com]
Sent: Thursday, October 08, 2009 7:12 AM
To: c-users@xerces.apache.org
Subject: Reading portions of XML file.

Hi,

I want to read the portions of XML file depending on byte-position, using getSrcOffset(). Is there a way I can directly start reading/parsing from a pre-defined offset in the source, similar to lseek and read?

Thanks.

Manish

RE: Reading portions of XML file.

Posted by John Lilley <jl...@datalever.com>.
Er, a bit cleaner snippet:

You can subclass InputSource and InputStream, then implement it however you like.  In this snippet, XN:: is defined as the Xerces namespace.

class MyFileInputStream : public XN::BinInputStream {
public:
	MyFileInputStream(...) {}
	virtual XMLFilePos curPos() const { return ... }
	virtual XMLSize_t readBytes(XMLByte* const toFill, const XMLSize_t maxToRead) {
		return ...;
	}
	// No "out-of-band" content type
	virtual const XMLCh* getContentType() const { return 0; }
private:
	...
};
class MyFileInputSource : public XN::InputSource
{
public :
	MyFileInputSource(...) {}
	virtual XN::BinInputStream* makeStream() const {
		// Caller is owner of stream
		return new MyFileInputStream(...);
	}
private:
	...
};

john

-----Original Message-----
From: Galande, Manish [mailto:Manish_Galande@bmc.com] 
Sent: Thursday, October 08, 2009 7:12 AM
To: c-users@xerces.apache.org
Subject: Reading portions of XML file.

Hi,

I want to read the portions of XML file depending on byte-position, using getSrcOffset(). Is there a way I can directly start reading/parsing from a pre-defined offset in the source, similar to lseek and read?

Thanks.

Manish

RE: Reading portions of XML file.

Posted by John Lilley <jl...@datalever.com>.
You can subclass InputSource and InputStream, then implement it however you like.  In this snippet, XN:: is defined as the Xerces namespace.

class MyFileInputStream : public XN::BinInputStream {
public:
	MyFileInputStream(...) {}
	virtual XMLFilePos curPos() const { return ... }
	virtual XMLSize_t readBytes(XMLByte* const toFill, const XMLSize_t maxToRead) {
		return ...;
	}
	// No "out-of-band" content type
	virtual const XMLCh* getContentType() const { return 0; }
private:
	...
};
class DL_GLOBAL_CLASS SaxFileInputSource : public XN::InputSource
{
public :
	MyFileInputSource(...) {}
	virtual XN::BinInputStream* makeStream() const {
		// Caller is owner of stream
		return new MyFileInputStream(...);
	}
private:
	...
};

john

-----Original Message-----
From: Galande, Manish [mailto:Manish_Galande@bmc.com] 
Sent: Thursday, October 08, 2009 7:12 AM
To: c-users@xerces.apache.org
Subject: Reading portions of XML file.

Hi,

I want to read the portions of XML file depending on byte-position, using getSrcOffset(). Is there a way I can directly start reading/parsing from a pre-defined offset in the source, similar to lseek and read?

Thanks.

Manish

Re: Xerces support for HP new Itanium OS

Posted by David Bertoni <db...@apache.org>.
Dantzler, DeWayne C wrote:
> Hello
> 
> Is there a version of Xerces that will compile on the latest version of HP's Unix-based HP-UX operating system for Intel's family of Itanium processors,HP-UX 11i Version 2? 
Xerces-C 2.8 and 3.x both compile with HP's aCC on Itanium.

Dave

Xerces support for HP new Itanium OS

Posted by "Dantzler, DeWayne C" <de...@boeing.com>.
Hello

Is there a version of Xerces that will compile on the latest version of HP's Unix-based HP-UX operating system for Intel's family of Itanium processors,HP-UX 11i Version 2? 

DeWayne Dantlzer

Re: Reading portions of XML file.

Posted by David Bertoni <db...@apache.org>.
Galande, Manish wrote:
> Hi,
> 
> I want to read the portions of XML file depending on byte-position, using getSrcOffset(). Is there a way I can directly start reading/parsing from a pre-defined offset in the source, similar to lseek and read?
You can write custom InputSource and BinInputStream derivatives that 
filter out the portions of the stream you're not interested in. 
However, you need to make sure the portion you are interested in is a 
well-formed XML document.

Dave