Introduction

Quick start

Here there is a small collection of code snippets to help the reader begin using pugixml.

For everything you can do with pugixml, you need a document. There are several ways to obtain it:

#include <fstream>
#include <iostream>

#include "pugixml.hpp"

using namespace std;
using namespace pugi;

int main()
{
    // Several ways to get XML document

    {
        // Load from string
        xml_document doc;

        cout << doc.load("<sample-xml>some text <b>in bold</b> here</sample-xml>") << endl;
    }

    {
        // Load from file
        xml_document doc;

        cout << doc.load_file("sample.xml") << endl;
    }

    {
        // Load from any input stream (STL)
        xml_document doc;

        std::ifstream in("sample.xml");
        cout << doc.load(in) << endl;
    }

    {
        // More advanced: parse the specified string without duplicating it
        xml_document doc;

        char* s = new char[100];
        strcpy(s, "<sample-xml>some text <b>in bold</b> here</sample-xml>");
        cout << doc.parse(transfer_ownership_tag(), s) << endl;
    }

    {
        // Even more advanced: assume manual lifetime control
        xml_document doc;

        char* s = new char[100];
        strcpy(s, "<sample-xml>some text <b>in bold</b> here</sample-xml>");
        cout << doc.parse(s) << endl;

        delete[] s; // <-- after this point, all string contents of document is invalid!
    }

    {
        // Or just create document from code?
        xml_document doc;

        // add nodes to document (see next samples)
    }
}

This sample should print a row of 1, meaning that all load/parse functions returned true (of course, if sample.xml does not exist or is malformed, there will be 0's)

Once you have your document, there are several ways to extract data from it.

#include <iostream>

#include "pugixml.hpp"

using namespace std;
using namespace pugi;

struct bookstore_traverser: public xml_tree_walker
{
    virtual bool for_each(xml_node& n)
    {
        for (int i = 0; i < depth(); ++i) cout << "  "; // indentation

        if (n.type() == node_element) cout << n.name() << endl;
        else cout << n.value() << endl;

        return true; // continue traversal
    }
};

int main()
{
    xml_document doc;
    doc.load("<bookstore><book title='ShaderX'><price>3</price></book><book title='GPU Gems'><price>4</price></book></bookstore>");

    // If you want to iterate through nodes...

    {
        // Get a bookstore node
        xml_node bookstore = doc.child("bookstore");

        // Iterate through books
        for (xml_node book = bookstore.child("book"); book; book = book.next_sibling("book"))
        {
            cout << "Book " << book.attribute("title").value() << ", price " << book.child("price").first_child().value() << endl;
        }

        // Output:
        // Book ShaderX, price 3
        // Book GPU Gems, price 4
    }

    {
        // Alternative way to get a bookstore node (wildcards)
        xml_node bookstore = doc.child_w("*[sS]tore"); // this will select bookstore, anyStore, Store, etc.

        // Iterate through books with STL compatible iterators
        for (xml_node::iterator it = bookstore.begin(); it != bookstore.end(); ++it)
        {
            // Note the use of helper function child_value()
            cout << "Book " << it->attribute("title").value() << ", price " << it->child_value("price") << endl;
        }
        
        // Output:
        // Book ShaderX, price 3
        // Book GPU Gems, price 4
    }

    {
        // You can also traverse the whole tree (or a subtree)
        bookstore_traverser t;

        doc.traverse(t);
        
        // Output:
        // bookstore
        //   book
        //     price
        //       3
        //   book
        //     price
        //       4

        doc.first_child().traverse(t);

        // Output:
        // book
        //   price
        //     3
        // book
        //   price
        //     4
    }

    // If you want a distinct node...

    {
        // You can specify the way to it through child() functions
        cout << doc.child("bookstore").child("book").next_sibling().attribute("title").value() << endl;

        // Output:
        // GPU Gems
    
        // You can use a sometimes convenient path function
        cout << doc.first_element_by_path("bookstore/book/price").child_value() << endl;
        
        // Output:
        // 3

        // And you can use powerful XPath expressions
        cout << doc.select_single_node("/bookstore/book[@title = 'ShaderX']/price").node().child_value() << endl;
        
        // Output:
        // 3

        // Of course, XPath is much more powerful

        // Compile query that prints total price of all Gems book in store
        xpath_query query("sum(/bookstore/book[contains(@title, 'Gems')]/price)");

        cout << query.evaluate_number(doc) << endl;

        // Output:
        // 4

        // You can apply the same XPath query to any document. For example, let's add another Gems
        // book (more detail about modifying tree in next sample):
        xml_node book = doc.child("bookstore").append_child();
        book.set_name("book");
        book.append_attribute("title") = "Game Programming Gems 2";
        
        xml_node price = book.append_child();
        price.set_name("price");

        xml_node price_text = price.append_child(node_pcdata);
        price_text.set_value("5.3");
    
        // Now let's reevaluate query
        cout << query.evaluate_number(doc) << endl;

        // Output:
        // 9.3
    }
}

Finally, let's get into more details about tree modification and saving.

#include <iostream>

#include "pugixml.hpp"

using namespace std;
using namespace pugi;

int main()
{
    // For this example, we'll start with an empty document and create nodes in it from code
    xml_document doc;

    // Append several children and set values/names at once
    doc.append_child(node_comment).set_value("This is a test comment");
    doc.append_child().set_name("application");

    // Let's add a few modules
    xml_node application = doc.child("application");

    // Save node wrapper for convenience
    xml_node module_a = application.append_child();
    module_a.set_name("module");
    
    // Add an attribute, immediately setting it's value
    module_a.append_attribute("name").set_value("A");

    // You can use operator=
    module_a.append_attribute("folder") = "/work/app/module_a";

    // Or even assign numbers
    module_a.append_attribute("status") = 85.4;

    // Let's add another module
    xml_node module_c = application.append_child();
    module_c.set_name("module");
    module_c.append_attribute("name") = "C";
    module_c.append_attribute("folder") = "/work/app/module_c";

    // Oh, we missed module B. Not a problem, let's insert it before module C
    xml_node module_b = application.insert_child_before(node_element, module_c);
    module_b.set_name("module");
    module_b.append_attribute("folder") = "/work/app/module_b";

    // We can do the same thing for attributes
    module_b.insert_attribute_before("name", module_b.attribute("folder")) = "B";
    
    // Let's add some text in module A
    module_a.append_child(node_pcdata).set_value("Module A description");

    // Well, there's not much left to do here. Let's output our document to file using several formatting options

    doc.save_file("sample_saved_1.xml");
    
    // Contents of file sample_saved_1.xml (tab size = 4):
    // <?xml version="1.0"?>
    // <!--This is a test comment-->
    // <application>
    //     <module name="A" folder="/work/app/module_a" status="85.4">Module A description</module>
    //     <module name="B" folder="/work/app/module_b" />
    //     <module name="C" folder="/work/app/module_c" />
    // </application>

    // Let's use two spaces for indentation instead of tab character
    doc.save_file("sample_saved_2.xml", "  ");

    // Contents of file sample_saved_2.xml:
    // <?xml version="1.0"?>
    // <!--This is a test comment-->
    // <application>
    //   <module name="A" folder="/work/app/module_a" status="85.4">Module A description</module>
    //   <module name="B" folder="/work/app/module_b" />
    //   <module name="C" folder="/work/app/module_c" />
    // </application>
    
    // Let's save a raw XML file
    doc.save_file("sample_saved_3.xml", "", format_raw);
    
    // Contents of file sample_saved_3.xml:
    // <?xml version="1.0"?><!--This is a test comment--><application><module name="A" folder="/work/app/module_a" status="85.4">Module A description</module><module name="B" folder="/work/app/module_b" /><module name="C" folder="/work/app/module_c" /></application>

    // Finally, you can print a subtree to any output stream (including cout)
    xml_writer_stream writer(cout);
    doc.child("application").child("module").print(writer);

    // Output:
    // <module name="A" folder="/work/app/module_a" status="85.4">Module A description</module>
}

Note, that these examples do not cover the whole pugixml API. For further information, look into reference section.

Reference

pugixml is a library for parsing XML files, which means that you give it XML data some way, and it gives you the DOM tree and the ways to traverse it and to get some useful information from it. The library source consist of two headers, pugixml.hpp and pugiconfig.hpp, and two source files, pugixml.cpp and pugixpath.cpp. You can either compile cpp files in your project, or build a static library. All library classes reside in namespace pugi, so you can either use fully qualified names (pugi::xml_node) or write a using declaration (using namespace pugi;, using pugi::xml_node) and use plain names. All classes have eitther xml_ or xpath_ prefix.

By default it's supposed that you compile the source file with your project (add it into your project, or add relevant entry in your Makefile, or do whatever you need to do with your compilation environment). The library is written in standard-conformant C++ and was tested on following platforms:

W3C compliance

pugixml is not a compliant XML parser. The main reason for that is that it does not reject most malformed XML files. The more or less complete list of incompatibilities follows (I will be talking of ones when using parse_w3c mode):

• The parser is completely DOCTYPE-ignorant, that is, it does not even skip all possible DOCTYPEs correctly, let alone use them for parsing
• It accepts multiple attributes with the same name in one node
• It is charset-ignorant
• It accepts invalid attribute values (those with < in them) and does not reject invalid entity references or character references (in fact, it does not do DOCTYPE parsing, so it does not perform entity reference expansion)
• It does not reject comments with -- inside
• It does not reject PI with the names of 'xml' and alike
• And some other things that I forgot to mention

Comparison with existing parsers

This table summarizes the comparison in terms of time and memory consumption between pugixml and other parsers. For DOM parsers (all, except Expat, irrXML and SAX parser of XercesC), the process is as follows:

• construct DOM tree from file, which is preloaded in memory (all parsers take const char* and size as an input). 'parse time' means number of CPU clocks which is spent, 'parse allocs' - number of allocations, 'parse memory' - peak memory consumption
• traverse DOM tree to fill information from it into some structure (which is the same for all parsers, of course). 'walk time' means number of CPU clocks which is spent, 'walk allocs' - number of allocations

For SAX parsers, the parse step is skipped (hence the N/A in relevant table cells), structure is filled during 'walk' step.

For all parsers, 'total time' column means total time spent on the whole process, 'total allocs' - total allocation count, 'total memory' - peak memory consumption for the whole process.

The tests were performed on a 1 Mb XML file with a small amount of text. They were compiled with Microsoft Visual C++ 8.0 (2005) compiler in Release mode, with checked iterators/secure STL turned off. The test system is AMD Sempron 2500+, 512 Mb RAM.

Note, that non-destructive parsing mode was just a test and is not yet in pugixml.

FAQ

Q: I do not have/want STL support. How can I compile pugixml without STL?

A: There is an undocumented define PUGIXML_NO_STL. If you uncomment the relevant line in pugixml header file, it will compile without any STL classes. The reason it is undocumented are that it will make some documented functions not available (specifically, xml_document::load, that operates on std::istream, xml_node::path function, XPath-related functions and classes and as_utf16/as_utf8 conversion functions). Otherwise, it will work fine.

Q: Do paths that are accepted by first_element_by_path have to end with delimiter?

A: Either way will work, both /path/to/node/ and /path/to/node is fine.

Bugs

Future work

Here are some improvements that will be done in future versions (they are sorted by priority, the upper ones will get there sooner).

• Support for UTF-16 files (parsing BOM to get file's type and converting UTF-16 file to UTF-8 buffer if necessary)
• More intelligent parsing of DOCTYPE (it does not always skip DOCTYPE for now)
• XML 1.1 changes (changed EOL handling, normalization issues, etc.)
• Name your own?

Changelog

15.07.2006 - v0.1

First private release for testing purposes

6.11.2006 - v0.2

First public release. Changes:

• Introduced child_value(name) and child_value_w(name)
• Fixed child_value() (for empty nodes)
• Fixed xml_parser_impl warning at W4
• parse_eol_pcdata and parse_eol_attribute flags + parse_minimal optimizations
• Optimizations of strconv_t

21.02.2007 - v0.3

Refactored, reworked and improved version. Changes:

• Interface:
  • Added XPath
  • Added tree modification functions
  • Added no STL compilation mode
  • Added saving document to file
  • Refactored parsing flags
  • Removed xml_parser class in favor of xml_document
  • Added transfer ownership parsing mode
  • Modified the way xml_tree_walker works
  • Iterators are now non-constant
• Implementation:
  • Support of several compilers and platforms
  • Refactored and sped up parsing core
  • Improved standard compliancy
  • Added XPath implementation
  • Fixed several bugs

31.10.2007 - v0.34

Maintenance release. Changes:

• Improved compatibility (supported Digital Mars C++, MSVC 6, CodeWarrior 8, PGI C++, Comeau, supported PS3 and XBox360)
• Fixed bug with loading from text-mode iostreams
• Fixed leak when transfer_ownership is true and parsing is failing
• Fixed bug in saving (\r and \n are now escaped in attribute values)
• PUGIXML_NO_EXCEPTION flag for platforms without exception handling
• Renamed free() to destroy() - some macro conflicts were reported

18.01.2009 - v0.4

Changes:

• Bugs:
  • Documentation fix in samples for parse() with manual lifetime control
  • Fixed document order sorting in XPath (it caused wrong order of nodes after xpath_node_set::sort and wrong results of some XPath queries)
• Node printing changes:
  • Single quotes are no longer escaped when printing nodes
  • Symbols in second half of ASCII table are no longer escaped when printing nodes; because of this, format_utf8 flag is deleted as it's no longer needed and format_write_bom is renamed to format_write_bom_utf8.
  • Reworked node printing - now it works via xml_writer interface; implementations for FILE* and std::ostream are available. As a side-effect, xml_document::save_file now works without STL.
• New features:
  • Added unsigned integer support for attributes (xml_attribute::as_uint, xml_attribute::operator=)
  • Now document declaration (<?xml ...?>) is parsed as node with type node_declaration when parse_declaration flag is specified (access to encoding/version is performed as if they were attributes, i.e. doc.child("xml").attribute("version").as_float()); corresponding flags for node printing were also added
  • Added support for custom memory management (see set_memory_management_functions for details)
  • Implemented node/attribute copying (see xml_node::insert_copy_* and xml_node::append_copy for details)
  • Added find_child_by_attribute and find_child_by_attribute_w to simplify parsing code in some cases (i.e. COLLADA files)
  • Added file offset information querying for debugging purposes (now you're able to determine exact location of any xml_node in parsed file, see xml_node::offset_debug for details)
  • Improved error handling for parsing - now load(), load_file() and parse() return xml_parse_result, which contains error code and last parsed offset; this does not break old interface as xml_parse_result can be implicitly casted to bool.

Acknowledgements

License

The pugixml parser is distributed under the MIT license:

Copyright (c) 2006-2007 Arseny Kapoulkine

Permission is hereby granted, free of charge, to any person
obtaining a copy of this software and associated documentation
files (the "Software"), to deal in the Software without
restriction, including without limitation the rights to use,
copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the
Software is furnished to do so, subject to the following
conditions:

The above copyright notice and this permission notice shall be
included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
OTHER DEALINGS IN THE SOFTWARE.

Revised 18 January, 2009