How to Work with XML Processing in C++

Aspose.Cells FOSS for C++ includes a lightweight XML processing layer used internally for reading and writing Open XML parts. The XmlDocument, XmlElement, and XmlAttribute classes provide programmatic access to XML data. This guide covers loading XML, traversing elements, and serializing documents.

Step-by-Step Guide

Step 1: Set Up the Build

cmake_minimum_required(VERSION 3.15)
project(XmlProcessing CXX)
set(CMAKE_CXX_STANDARD 17)

add_subdirectory(path/to/Aspose.Cells-FOSS-for-Cpp)
add_executable(XmlProcessing main.cpp)
target_link_libraries(XmlProcessing PRIVATE Aspose.Cells.Foss.Cpp)

Step 2: Include Headers

#include "aspose/cells_foss/XmlDocument.h"
#include "aspose/cells_foss/XmlElement.h"
#include "aspose/cells_foss/XmlAttribute.h"

using namespace Aspose::Cells_FOSS;

Step 3: Load an XML Document

Use XmlDocument::Load to parse an XML string into the in-memory document tree:

int main() {
    XmlDocument doc;
    doc.Load("<root><item key=\"a\">Hello</item><item key=\"b\">World</item></root>");
    return 0;
}

Step 4: Check for Null Elements

XmlElement uses a handle-based model — an element returned from a missing path is null. Always check IsNull() before accessing data:

XmlElement root = doc.GetRootElement();
if (!root.IsNull()) {
    std::string val = root.GetValue();
}

Step 5: Traverse Attributes

Use XmlElement::GetAttributes() to retrieve the attribute collection. Each attribute handle exposes its name and value:

auto attrs = root.GetAttributes();
for (auto& attr : attrs) {
    bool isNull = attr.IsNull();
}

Step 6: Serialize to UTF-8 String

Use XmlDocument::SaveToUtf8() to get the serialized XML:

std::string xml = doc.SaveToUtf8();

Step 7: Handle Parse Errors

Wrap XmlDocument::Load in a try/catch block when processing untrusted XML:

try {
    doc.Load(xmlContent);
} catch (const XmlParsingException& ex) {
    // Handle malformed XML
}

Common Issues and Fixes

IsNull() returns true unexpectedly The element path does not exist in the document. Verify the XML structure matches your expected schema before traversal.

XmlParsingException on load The input is malformed or contains unsupported entities. Validate the XML with an external tool before passing it to Load.

SaveToUtf8() returns unexpected output The document structure was modified after Load. Verify all intermediate Build operations completed correctly.

Attributes not found Attribute lookup is case-sensitive. Verify the attribute name matches exactly as it appears in the XML source.

Empty result from GetValue() Text nodes that contain only whitespace may return an empty string. Check the raw XML to confirm the element has non-whitespace content.

Frequently Asked Questions

Is the XML layer intended for application use or internal use only?

The XmlDocument, XmlElement, and XmlAttribute classes are part of the public API and can be used directly. The mapper classes (WorkbookXmlMapper, WorksheetXmlMapper, etc.) are internal helpers called by XlsxWorkbookSerializer and are not intended for direct use.

Can I build a new XML document from scratch?

Yes. Use XmlDocument::Build to construct a document programmatically, then use XmlElement and XmlAttribute::MakeAttribute to add nodes.

Does `XmlDocument` support XPath queries?

No. The current implementation provides element handle traversal only; XPath is not supported.

What encoding does `SaveToUtf8()` produce?

The output is always UTF-8 encoded XML. The XML declaration (<?xml version="1.0" encoding="UTF-8"?>) is included in the output.

Can I use `XmlDocument` to read XLSX archive parts?

The XLSX archive parts are managed internally by XlsxWorkbookSerializer. There is no public API to extract raw archive parts. Use Workbook for all XLSX load/save operations.