Fast start to XML in C++

Enough bull. You want to create XML or read and find things in XML. All you need to know about CMarkup is that it is just one object per XML document (for the API design concept see EDOM). And by the way the free firstobject XML Editor generates C++ source code for creating and navigating your own XML documents with CMarkup.

Creating an XML Document

To create an XML document, instantiate a CMarkup object and call AddElem to create the root element. At this point your document would simply contain the empty root element e.g. <ORDER/>. Then call IntoElem to go "inside" the ORDER element so that you can create child elements under the root element (i.e. the root element will be the "container" of the child elements).

The following example code creates an XML document.

CMarkup xml;
xml.AddElem( "ORDER" );
xml.IntoElem();
xml.AddElem( "ITEM" );
xml.IntoElem();
xml.AddElem( "SN", "132487A-J" );
xml.AddElem( "NAME", "crank casing" );
xml.AddElem( "QTY", "1" );

This code generates the following XML. The root is the ORDER element; notice that its start tag <ORDER> is at the beginning and end tag </ORDER> is at the bottom. When an element is under (i.e. inside or contained by) a parent element, the parent's start tag is before it and the parent's end tag is after it. The ORDER element contains one ITEM element. That ITEM element contains 3 child elements: SN, NAME, and QTY.

<ORDER>
<ITEM>
<SN>132487A-J</SN>
<NAME>crank casing</NAME>
<QTY>1</QTY>
</ITEM>
</ORDER>

As shown in the example, you create elements under an element by calling IntoElem to make your current main position (or "place holder") into your current parent position so you can begin adding child elements. CMarkup maintains a current position in order to keep your source code shorter and simpler. This same position logic is used when navigating a document.

You can write the above document to file with Save:

xml.Save( "C:\\Sample.xml" );

And you can retrieve the XML into a string with GetDoc:

MCD_STR strXML = xml.GetDoc();

Markup.h defines MCD_STR to the string type you compile CMarkup for, so we use MCD_STR in these examples, but you can use your own string type explicitly (e.g. std::string or CString).

Navigating an XML Document

You can navigate the data right inside the same CMarkup object you created in the example above; just call ResetPos if you want to go back to the beginning of the document. Or you can populate a new CMarkup object:

CMarkup xml;

From a file with Load:

xml.Load( "C:\\Sample.xml" );

Or from an XML string with SetDoc:

xml.SetDoc( strXML );

In the following example, we go inside the root ORDER element and loop through all ITEM elements with FindElem to get the serial number and quantity of each with GetData. The serial number is treated as a string and the quantity is converted to an integer using atoi (MCD_2PCSZ is defined in Markup.h to return the string's const pointer).

xml.FindElem(); // root ORDER element
xml.IntoElem(); // inside ORDER
while ( xml.FindElem("ITEM") )
{
    xml.IntoElem();
    xml.FindElem( "SN" );
    MCD_STR strSN = xml.GetData();
    xml.FindElem( "QTY" );
    int nQty = atoi( MCD_2PCSZ(xml.GetData()) );
    xml.OutOfElem();
}

For each item we find, we call IntoElem to interrogate its child elements, and then OutOfElem afterwards. As you get accustomed to this type of navigation you will know to check in your loops to make sure there is a corresponding OutOfElem call for every IntoElem call.

Adding Elements and Attributes

The above example for creating a document only created one ITEM element. Here is an example that creates multiple items loaded from a previously populated data source, plus a SHIPMENT information element in which one of the elements has an attribute we set with SetAttrib.

CMarkup xml;
xml.AddElem( "ORDER" );
xml.IntoElem(); // inside ORDER
for ( int nItem=0; nItem<aItems.GetSize(); ++nItem )
{
    xml.AddElem( "ITEM" );
    xml.IntoElem(); // inside ITEM
    xml.AddElem( "SN", aItems[nItem].strSN );
    xml.AddElem( "NAME", aItems[nItem].strName );
    xml.AddElem( "QTY", aItems[nItem].nQty );
    xml.OutOfElem(); // back out to ITEM level
}
xml.AddElem( "SHIPMENT" );
xml.IntoElem(); // inside SHIPMENT
xml.AddElem( "POC" );
xml.SetAttrib( "type", strPOCType );
xml.IntoElem(); // inside POC
xml.AddElem( "NAME", strPOCName );
xml.AddElem( "TEL", strPOCTel );

This code generates the following XML. The root ORDER element contains 2 ITEM elements and a SHIPMENT element. The ITEM elements both contain SN, NAME and QTY elements. The SHIPMENT element contains a POC element which has a type attribute, and NAME and TEL child elements.

<ORDER>
<ITEM>
<SN>132487A-J</SN>
<NAME>crank casing</NAME>
<QTY>1</QTY>
</ITEM>
<ITEM>
<SN>4238764-A</SN>
<NAME>bearing</NAME>
<QTY>15</QTY>
</ITEM>
<SHIPMENT>
<POC type="non-emergency">
<NAME>John Smith</NAME>
<TEL>555-1234</TEL>
</POC>
</SHIPMENT>
</ORDER>

Finding Elements

The FindElem method goes to the next sibling element. If the optional tag name argument is specified, then it goes to the next element with a matching tag name. The element that is found becomes the current element, and the next call to FindElem will go to the next sibling or matching sibling after that current position.

When you cannot assume the order of the elements, you must move the position back before the first sibling with ResetMainPos in between your calls to the FindElem method. Looking at the ITEM element in the above example, if someone else is creating the XML and you cannot assume the SN element is before the QTY element, then call ResetMainPos before finding the QTY element.

{
    xml.IntoElem();
    xml.FindElem( "SN" );
    MCD_STR strSN = xml.GetData();
    xml.ResetMainPos();
    xml.FindElem( "QTY" );
    int nQty = atoi( MCD_2PCSZ(xml.GetData()) );
    xml.OutOfElem();
}

To find the item with a particular serial number, you can loop through the ITEM elements and compare the SN element data to the serial number you are searching for. By specifying the "ITEM" element tag name in the FindElem method we ignore all other sibling elements such as the SHIPMENT element. Also, instead of going into and out of the ITEM element to look for the SN child element, we use the FindChildElem and GetChildData methods for convenience.

xml.ResetPos(); // top of document
xml.FindElem(); // ORDER element is root
xml.IntoElem(); // inside ORDER
while ( xml.FindElem("ITEM") )
{
    xml.FindChildElem( "SN" );
    if ( xml.GetChildData() == strFindSN )
        break; // found
}

You are NOT on your own

This site has all kinds of examples of doing various XML operations. CMarkup has been widely used for many years. Of course it doesn't do everything, but almost every purpose has at least been discussed. Don't hesitate to ask if you have questions. A good place to go next is the CMarkup Methods.