Working with XML in C++: PugiXML and RapidXML Libraries |…

Working with XML in C++: PugiXML and RapidXML Libraries

XML (Extensible Markup Language) remains one of the key formats for storing and transmitting structured data. In C++, there are several powerful libraries for working with XML, among which PugiXML (lightweight, with XPath support) and RapidXML (extremely fast, working "in-place") stand out. In this article, we will cover both libraries, their features, installation, and practical examples.

1. PugiXML — A Versatile Tool

PugiXML is a lightweight, cross-platform library with support for XPath 1.0 and UTF-8/UTF-16 encodings. It is ideal for most tasks: from reading configuration files to complex analysis of XML documents.

Installation

Download the header files from the official website or use a package manager (vcpkg, Conan). Include in your project:

#include "pugixml.hpp"using namespace pugi;

Example: Loading and Reading XML

#include <iostream>#include "pugixml.hpp"

int main() {    xml_document doc;    if (!doc.load_file("config.xml")) {        std::cerr << "Error loading file";        return -1;    }

    // Get the root element    xml_node root = doc.child("settings");    for (xml_node node = root.child("param"); node; node = node.next_sibling("param")) {        std::string name = node.attribute("name").as_string();        int value = node.attribute("value").as_int();        std::cout << "Parameter: " << name << " = " << value << "";    }    return 0;}

Example: Creating an XML Document

xml_document doc;xml_node root = doc.append_child("catalog");for (int i = 1; i <= 3; ++i) {    xml_node item = root.append_child("item");    item.append_attribute("id") = i;    item.append_child("name").text() = ("Product " + std::to_string(i)).c_str();    item.append_child("price").text() = 100.0 * i;}doc.save_file("catalog.xml");

Advantages of PugiXML:

XPath support for complex queries (e.g., doc.select_nodes("//item[@id>1]")).
Encoding and Unicode support.
Detailed documentation and an active community.

2. RapidXML — Speed and Minimalism

RapidXML is a header-only library that parses XML without copying data (in-place). It works significantly faster than PugiXML, but does not support XPath and requires caution with string lifetimes.

Installation

Copy rapidxml.hpp and additional files (rapidxml_utils.hpp, rapidxml_print.hpp) into your project.

Example: Parsing a String

#include <iostream>#include "rapidxml.hpp"

int main() {    char xml[] = "<root><item id='1'>Value</item></root>";    rapidxml::xml_document<> doc;    doc.parse<0>(xml); // 0 — parsing flags

    rapidxml::xml_node<>* root = doc.first_node("root");    rapidxml::xml_node<>* item = root->first_node("item");    if (item) {        std::cout << "ID: " << item->first_attribute("id")->value() << "";        std::cout << "Content: " << item->value() << "";    }    return 0;}

Example: Creating XML

rapidxml::xml_document<> doc;rapidxml::xml_node<>* root = doc.allocate_node(rapidxml::node_element, "data");doc.append_node(root);

rapidxml::xml_node<>* child = doc.allocate_node(rapidxml::node_element, "value", "42");root->append_node(child);

// Output to stringstd::string result;rapidxml::print(std::back_inserter(result), doc);std::cout << result;

Important: