Small, simple, cross-platform, free and fast  C++ XML Parser

This project started from my frustration that I could not find any simple, portable XML Parser to use inside all my projects (for example, inside the award-winning TIMi software suite commercialized by the TIMi company). Let's look at the well-known Xerces C++ library: The complete Xerces project is 53 MB! (11 MB compressed in a zipfile). In 2003, I was developping many small tools. I was using XML as standard for all my input/ouput configuration and data files. The source code of my small tools was usually around 600KB. In these conditions, don't you think that 53MB to be able to read an XML file is a little bit "too much"? So I created my own XML parser. My XML parser "library" is composed of only 2 files: a .cpp file and a .h file. The total size is 149 KB.

Here is how it works: The XML parser loads a full XML file in memory, it parses the file and it generates a tree structure representing the XML file. Of course, you can also parse XML data that you have already stored yourself into a memory buffer. Thereafter, you can easily "explore" the tree to get your data. You can also modify the tree using "add" and "delete" functions < and regenerate a formatted XML string from a subtree. Memory management is totally transparent through the use of smart pointers (in other words, you will never have to do any new, delete, malloc or free)("Smart pointers" are a primitive version of the garbage collector in Java).

UPDATE: Based on the expertise gained during the development of this XML Parsing library, I create a new, improved XML Parser: the Incredible XML Parser. The Incredible XML Parser has all the nice features from the library described on this page AND it's even faster, more scalable, less memory-hungry and easier to use. To the best of my knowledge, the Incredible XML Parser is the best "non-validating C++ XML parser" currently available 😄 (and by a large margin!). You should definitively check it out!

Here are the characteristics of the (old) XMLparser library:
  • Non-validating XML parser written in standard C++ (DTD's or XSD's informations are ignored).
  • Cross-plateform: the library is currently used every day on Solaris, Linux (32bit and 64bit) and Windows to manipulate "small" PMML documents (10 MB).
    The library has been tested and is working flawlessly using the following compilers: gcc (under linux, Mac OS X Tiger and under many unix flavours), Visual Studio 6.0, Visual Studio .NET (under Windows 9x,NT,2000,XP,Vista,CE,mobile), Intel C/C++ compiler, SUN CC compiler, C++ Borland Compiler. The library is also used under Apple OS, iPhone/iPad OS, Amiga OS, QNX and under the Netburner plateform. To the best of my knowledge, i think that all plateforms are now supported.
  • The parser builds a tree structure that you can "explore" easily (DOM-type parser).
  • The parser can be used to generate XML strings from subtrees (it's called rendering). You can also save subtrees directly to files (automatic "Byte Order Mark"-BOM support).
  • Modification or "from scratch creation" of large XML tree structures in memory using funtions like addChild, addAttribute, updateAttribute, deleteAttribute,...
  • It's SIMPLE: no need to learn how to use dozens of classes: there is only one simple class: the 'XMLNode' class (that represents one node of the XML tree).
  • Quite efficient (Efficiency is required to be able to handle BIG files)...But my new XML Parser library (the Incredible XML Parser) is now several order of magnitude faster:
  • Complete In-memory parsing (as are 99% of the Dom-Style XML Parsers).
  • Supports XML namespaces
  • Very small and totally stand-alone (not built on top of something else). Uses only standard <stdio.h> library (and only for the 'fopen' and the 'fread' functions to load the XML file).
  • Easy to integrate into you own projects: it's only 2 files! The .h file does not contain any implementation code. Compilation is thus very fast.
  • Robust (We are using it every day the since 2004 inside the TIMi company).
    Optionnally, if you define the C++ prepocessor directives STRICT_PARSING and/or APPROXIMATE_PARSING, the library can be "forgiving" in case of errors inside the XML.
    I have tried to respect the XML-specs given at: http://www.w3.org/TR/REC-xml/
  • Fully integrated error handling :
  • Thread-safe (more precisely: reentrant). However there exists some global parameters (the "guessUnicodeChar" parameter, the "character Encoding" parameter, and the "strictUTF8Parsing" parameter) that you can't change because they are shared by all threads. My newest XML Parser library (the Incredible XML Parser) is 100% Thread-safe.
  • Full Native Supports for a wide range of Character Encodings: ANSI (legacy) / UTF-8 / Shift-JIS / GB2312 / Big5 / GBK.
    Under Windows, Linux, Linux 64 bits & Solaris, we have additionnaly: Unicode 16bit / Unicode 32bit widechar characters support that includes: The XMLParser library is able to handle successfuly chinese, japanese, cyrilic and other extended characters thanks to an extended UTF-8 encoding support, Shift-JIS (japanese) and to GB2312/Big5/GBK encoding support (chinese) (see this UTF-8-demo that shows the characters available). If you are still experiencing character encoding problems, I suggest you to convert your XML files to UTF-8 using a tool like iconv (precompiled win32 binary).
  • Transparent memory management through the use of smart pointers.
  • Limited Support for character entities. The current known character entities are:
    &lt; < less than
    &gt; > greater than
    &amp; & ampersand
    &apos; ' apostrophe
    &quot; " quotation mark
    &#x04B; K direct access to the ascii code of any character
    (in hexadecimal)
    &#75; K direct access to the ascii code of any character
    (in standard decimal)
  • Support for a wide range of clearTags that are containing unformatted text:
    <![CDATA[ ... ]]>, <!-- ... -->, <PRE> ... </PRE>, <!DOCTYPE ... >
    Unformatted texts are not parsed by the library and can contain items that are usually 'forbidden' in XML (for example: html code)
  • Support for inclusion of pure binary data (images, sounds,...) into the XML document using the four provided ultrafast Base64 conversion functions.
  • Nice & Complete Doxygen documentation.
  • The library is under the Aladdin Free Public License(AFPL).
    If you need another license,simply (I don't want any money for the XMLParser).
  • Easy to customize: The code is small, commented and written in a plain and simple way. Thus, if you really need to change something (but I doubt of it), it's easy.

    • Download

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    Download here: small, simple, multi-Plateform XMLParser library with examples (zipfile).
    Inside the zip file, you will find 5 examples: If you have a Kindle, you might also be interested in KKCM: the Kranf Kindle Collection Manager.

    Log

    Version changes:

    A small tutorial

    Let's assume that you want to parse the XML file "PMMLModel.xml" that contains: 

    <?xml version="1.0" encoding="ISO-8859-1"?>
    <PMML version="3.0"
      xmlns="http://www.dmg.org/PMML-3-0"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema_instance" >
      <Header copyright="Frank Vanden Berghen">
     Hello TIMi!
         <Application name="&lt;Condor>" version="1.99beta" />
      </Header>
  <Extension name="keys"> <Key name="urn"> </Key> </Extension>
      <DataDictionary>
        <DataField name="persfam" optype="continuous" dataType="double">
           <Value value="9.900000e+001" property="missing" />
        </DataField>
        <DataField name="prov" optype="continuous" dataType="double" />
        <DataField name="urb" optype="continuous" dataType="double" />
        <DataField name="ses" optype="continuous" dataType="double" />
      </DataDictionary>
      <RegressionModel functionName="regression" modelType="linearRegression">
        <RegressionTable intercept="0.00796037">
          <NumericPredictor name="persfam" coefficient="-0.00275951" />
          <NumericPredictor name="prov" coefficient="0.000319433" />
          <NumericPredictor name="ses" coefficient="-0.000454307" />
      <NONNumericPredictor name="testXmlExample" />
        </RegressionTable>
      </RegressionModel>
    </PMML>

    Let's analyse line by line the following small example program: 

    #include <stdio.h>    // to get "printf" function
#include <stdlib.h>   // to get "free" function
#include "xmlParser.h"

int main(int argc, char **argv)
{
  // this open and parse the XML file:
      XMLNode xMainNode=XMLNode::openFileHelper("PMMLModel.xml","PMML");
    
  // this prints "<Condor>":
  XMLNode xNode=xMainNode.getChildNode("Header");
  printf("Application Name is: '%s'\n", xNode.getChildNode("Application").getAttribute("name"));
      
  // this prints "Hello TIMi!":
  printf("Text inside Header tag is :'%s'\n", xNode.getText());
    
  // this gets the number of "NumericPredictor" tags:
      xNode=xMainNode.getChildNode("RegressionModel").getChildNode("RegressionTable");
  int n=xNode.nChildNode("NumericPredictor");

  // this prints the "coefficient" value for all the "NumericPredictor" tags:
      for (int i=0; i<n; i++)
    printf("coeff %i=%f\n",i+1,atof(xNode.getChildNode("NumericPredictor",i).getAttribute("coefficient")));

  // this prints a formatted ouput based on the content of the first "Extension" tag of the XML file:
      char *t=xMainNode.getChildNode("Extension").createXMLString(true);
      printf("%s\n",t);
      free(t);
  return 0;
    }

    To manipulate the data contained inside the XML file, the first operation is to get an instance of the class XMLNode that is representing the XML file in memory. You can use: 

    XMLNode xMainNode=XMLNode::openFileHelper("PMMLModel.xml","PMML");
    or, if you use the UNICODE windows version of the library: 
    XMLNode xMainNode=XMLNode::openFileHelper("PMMLModel.xml",_T("PMML"));
    or, if the XML document is already in a memory buffer pointed by variable "char *xmlDoc" : 
    XMLNode xMainNode=XMLNode::parseString(xmlDoc,"PMML");
    This will create an object called xMainNode that represents the first tag named PMML found inside the XML document. This object is the top of tree structure representing the XML file in memory. The following command creates a new object called xNode that represents the "Header" tag inside the "PMML" tag. 

    XMLNode xNode=xMainNode.getChildNode("Header");
    The following command prints on the screen "<Condor>" (note that the "&lt;" character entity has been replaced by "<"): 
    printf("Application Name is: '%S'\n", xNode.getChildNode("Application").getAttribute("name"));
    The following command prints on the screen "Hello TIMi!": 
    printf("Text inside Header tag is :'%s'\n", xNode.getText());
    Let's assume you want to "go to" the tag named "RegressionTable": 

    xNode=xMainNode.getChildNode("RegressionModel").getChildNode("RegressionTable");

    Note that the previous value of the object named xNode has been "garbage collected" so that no memory leak occurs. If you want to know how many tags named "NumericPredictor" are contained inside the tag named "RegressionTable":

    int n=xNode.nChildNode("NumericPredictor");

    The variable n now contains the value 3. If you want to print the value of the coefficient attribute for all the NumericPredictor tags:

    and TIM
    for (int i=0; i<n; i++)
  printf("coeff %i=%f\n",i+1,atof(xNode.getChildNode("NumericPredictor",i).getAttribute("coefficient")));
    Or equivalently, but faster at runtime:
    int iterator=0;
for (int i=0; i<n; i++)
  printf("coeff %i=%f\n",i+1,atof(xNode.getChildNode("NumericPredictor",&iterator).getAttribute("coefficient")));

    If you want to generate and print on the screen the following XML formatted text: 

    <Extension name="keys">
  <Key name="urn" />
</Extension>

    You can use: 

    char *t=xMainNode.getChildNode("Extension").createXMLString(true);
    printf("%s\n",t);
    free(t);

    Note that you must free the memory yourself (using the "free(t);" function) : only the XMLNode objects and their contents are "garbage collected". The parameter true to the function createXMLString means that we want formatted output.


    The XML Parser library contains many more other small usefull methods that are not described here (The zip file contains some additional examples to explain other functionalities and a complete Doxygen documentation about the XMParser.). These methods allows you to: That's all folks! With this basic knowledge, you should be able to retreive easily any data from any XML file!