Problem in editing xml file through Dom parser.

[Niamita]

Hi all

i am in a trouble. My xml file is not edit right. Whem i am editing the file the contents to be edit are written in file with the rest data of file again. I am using Dom for reading and writing xml.

My code is

void HomeWindow::create_xml_file()
{
    QFile *file = new QFile("E:/new.txt");
    if(!edit_flag){ /// craeting the file and write in it in this condition
    const int Indent = 4;
    int id_value;
    static QDomDocument doc;
    static QDomElement root,root1;
    QDomElement statement, action_node, condition_node;
    QDomText id_text;
    root = doc.createElement("root");
 
    if(!file->exists())
    {
	file->open(QIODevice::WriteOnly);
	QDomElement id = doc.createElement("id");
	id_text = doc.createTextNode("0");
	root.appendChild(id);
	id.appendChild(id_text);
	doc.appendChild(root);
    }
    else
    {
	file->open(QFile::ReadWrite);
	doc.setContent(file);
	root1 = doc.documentElement();
	QDomElement node = root1.firstChildElement("id");
	QString id_string = node.text();
	id_value = id_string.toInt();
	QDomElement new_id_node = doc.createElement(QString("id"));
	QDomText new_id_Text = doc.createTextNode(QString::number(++id_value));
	new_id_node.appendChild(new_id_Text);  // replace existing node with new node
	root1.replaceChild(new_id_node, node);
	statement = doc.createElement("statement");
	condition_node = doc.createElement("condition");
	action_node = doc.createElement("action");
	QDomText condition_text = doc.createTextNode(condition_text_edit->toPlainText());
	QDomText action_text = doc.createTextNode(action_text_edit->toPlainText());
	statement.setAttribute("id", id_value);
	statement.appendChild(condition_node);
	statement.appendChild(action_node);
	condition_node.appendChild(condition_text);
	action_node.appendChild(action_text);
	root1.appendChild(statement);
	file->seek(0);
	static int i =1;
	table->setRowCount(i);
	QTableWidgetItem *item_id = new QTableWidgetItem(QString::number(id_value));
	QTableWidgetItem *item_condition = new QTableWidgetItem(condition_text_edit->toPlainText());
	QTableWidgetItem *item_action = new QTableWidgetItem(action_text_edit->toPlainText());
	int row = i;
	row = --row;
	table->setItem(row, 0, item_id);
	table->setItem(row, 1, item_condition);
	table->setItem(row, 2, item_action);
	i++;
	condition_text_edit->clear();
	action_text_edit->clear();
    }
    QTextStream out(file);
    doc.save(out, Indent);
    if(file->error())
	qDebug()<<"error"<<file->errorString();
    }
    else{          ///////edit the file 
	const int indent  =8;
	QDomDocument doc;
	file->open(QFile::ReadWrite);
	doc.setContent(file);
	QDomElement root_edit = doc.documentElement();
	QDomNode node = root_edit.firstChild();
	while(!node.isNull())
	{
	    if (node.toElement().tagName() == "statement"){
		if(string_id == node.toElement().attribute("id"))
		{
		    QDomElement statement = doc.createElement("statement");
		    statement.setAttribute("id", string_id);
		    QDomElement condition_node = doc.createElement("condition");
		    QDomElement action_node = doc.createElement("action");
		    QDomText condition_text = doc.createTextNode(condition_text_edit->toPlainText());
		    QDomText action_text = doc.createTextNode(action_text_edit->toPlainText());
		    statement.appendChild(condition_node);
		    statement.appendChild(action_node);
		    condition_node.appendChild(condition_text);
		    action_node.appendChild(action_text);
		    root_edit.replaceChild(statement, node.toElement());
		    break;
		}
	    }
	node = node.nextSibling();
	}
	QTextStream out(file);
	doc.save(out, indent);
	QTableWidgetItem *item_id = new QTableWidgetItem(string_id);
	QTableWidgetItem *item_condition = new QTableWidgetItem(condition_text_edit->toPlainText());
	QTableWidgetItem *item_action = new QTableWidgetItem(action_text_edit->toPlainText());
	table->setItem(row_index, 0, item_id);
	table->setItem(row_index, 1, item_condition);
	table->setItem(row_index, 2, item_action);
	condition_text_edit->clear();
	action_text_edit->clear();
	edit_flag = false;
    }
}

void HomeWindow::create_xml_file()
{
    QFile *file = new QFile("E:/new.txt");
    if(!edit_flag){ /// craeting the file and write in it in this condition
    const int Indent = 4;
    int id_value;
    static QDomDocument doc;
    static QDomElement root,root1;
    QDomElement statement, action_node, condition_node;
    QDomText id_text;
    root = doc.createElement("root");

    if(!file->exists())
    {
	file->open(QIODevice::WriteOnly);
	QDomElement id = doc.createElement("id");
	id_text = doc.createTextNode("0");
	root.appendChild(id);
	id.appendChild(id_text);
	doc.appendChild(root);
    }
    else
    {
	file->open(QFile::ReadWrite);
	doc.setContent(file);
	root1 = doc.documentElement();
	QDomElement node = root1.firstChildElement("id");
	QString id_string = node.text();
	id_value = id_string.toInt();
	QDomElement new_id_node = doc.createElement(QString("id"));
	QDomText new_id_Text = doc.createTextNode(QString::number(++id_value));
	new_id_node.appendChild(new_id_Text);  // replace existing node with new node
	root1.replaceChild(new_id_node, node);
	statement = doc.createElement("statement");
	condition_node = doc.createElement("condition");
	action_node = doc.createElement("action");
	QDomText condition_text = doc.createTextNode(condition_text_edit->toPlainText());
	QDomText action_text = doc.createTextNode(action_text_edit->toPlainText());
	statement.setAttribute("id", id_value);
	statement.appendChild(condition_node);
	statement.appendChild(action_node);
	condition_node.appendChild(condition_text);
	action_node.appendChild(action_text);
	root1.appendChild(statement);
	file->seek(0);
	static int i =1;
	table->setRowCount(i);
	QTableWidgetItem *item_id = new QTableWidgetItem(QString::number(id_value));
	QTableWidgetItem *item_condition = new QTableWidgetItem(condition_text_edit->toPlainText());
	QTableWidgetItem *item_action = new QTableWidgetItem(action_text_edit->toPlainText());
	int row = i;
	row = --row;
	table->setItem(row, 0, item_id);
	table->setItem(row, 1, item_condition);
	table->setItem(row, 2, item_action);
	i++;
	condition_text_edit->clear();
	action_text_edit->clear();
    }
    QTextStream out(file);
    doc.save(out, Indent);
    if(file->error())
	qDebug()<<"error"<<file->errorString();
    }
    else{          ///////edit the file 
	const int indent  =8;
	QDomDocument doc;
	file->open(QFile::ReadWrite);
	doc.setContent(file);
	QDomElement root_edit = doc.documentElement();
	QDomNode node = root_edit.firstChild();
	while(!node.isNull())
	{
	    if (node.toElement().tagName() == "statement"){
		if(string_id == node.toElement().attribute("id"))
		{
		    QDomElement statement = doc.createElement("statement");
		    statement.setAttribute("id", string_id);
		    QDomElement condition_node = doc.createElement("condition");
		    QDomElement action_node = doc.createElement("action");
		    QDomText condition_text = doc.createTextNode(condition_text_edit->toPlainText());
		    QDomText action_text = doc.createTextNode(action_text_edit->toPlainText());
		    statement.appendChild(condition_node);
		    statement.appendChild(action_node);
		    condition_node.appendChild(condition_text);
		    action_node.appendChild(action_text);
		    root_edit.replaceChild(statement, node.toElement());
		    break;
		}
	    }
	node = node.nextSibling();
	}
	QTextStream out(file);
	doc.save(out, indent);
	QTableWidgetItem *item_id = new QTableWidgetItem(string_id);
	QTableWidgetItem *item_condition = new QTableWidgetItem(condition_text_edit->toPlainText());
	QTableWidgetItem *item_action = new QTableWidgetItem(action_text_edit->toPlainText());
	table->setItem(row_index, 0, item_id);
	table->setItem(row_index, 1, item_condition);
	table->setItem(row_index, 2, item_action);
	condition_text_edit->clear();
	action_text_edit->clear();
	edit_flag = false;
    }
}

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My xml file is looking like following

<root>
<id>3</id>
<statement id="1">
<condition>Digital Input Equals to END</condition>
<action>Analog Output Equals to END</action>
</statement>
<statement id="2">
<condition>Digital Input Equals to END</condition>
<action>Analog Output Equals to END</action>
</statement>
<statement id="3">
<condition>Digital Input Equals to END</condition>
<action>Analog Output Equals to END</action>
</statement>
</root>
tput Equals to END</action>
</statement>
<statement id="2">
<condition>Digital Input Equals to END</condition>
<action>gffjryjuuyd</action>
</statement>
</root>
<root>
<id>3</id>
<statement id="1">
<condition>Digital Input Equals to END</condition>
<action>Analog Output Equals to END</action>
</statement>
<statement id="2">
<condition>Digital Input Equals to END</condition>
<action>Analog Output Equals to END</action>
</statement>
<statement id="3">
<condition>Digital Input Equals to END</condition>
<action>gjkghk</action>
</statement>
</root>


Please guide me where i am wrong.
Waiting for quick reply.
Thanks.

[wysota]

If a file is 10 bytes long and you seek to the beginning and write 8 bytes, the file will remain to be 10 bytes long -- you will only modify the first 8 bytes, leaving the last two unchanged. If you want to discard the remaining bytes, you need to truncate the file.

[Niamita]

but i did not seek the file at the time of editing. Have you look at the xml file which generate after editing it.
Please give me some sample code.
Thanks.

[wysota]

I have already said everything I had to say, you have all info you need, just make proper use of it -- this is not kindergarden. Analyze your own code and reach your own conclusions. I can only repeat -- if you want to have the file be shorter than it was before, you need to truncate the file. This is general programming knowledge, nothing related to Qt or even C++.

[ChrisW67]

but i did not seek the file at the time of editing.

Sure you did...

root1.appendChild(statement);
file->seek(0);
static int i =1;
table->setRowCount(i);

root1.appendChild(statement);
file->seek(0);
static int i =1;
table->setRowCount(i);

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The whole approach needs revision IMHO. Assuming the XML file is fairly small, the process is:

• Read the whole document in the DOM from disc or create an "empty" DOM document if no file exists yet
• Create/modify the document in the DOM using the relevant methods and whatever UI
• Write the whole DOM document back to disc overwriting the old file if one exists.

No fiddling about with read/write files or trying to update in-situ. You should be able to draw solid dividing lines between the three elements.

[wysota]

...and truncate the file if you intend to write less than the previous content of the file.