libexpatpp - a modern C++ xml parser toolkit using expat

Table of Contents

• Overview
• Features
• Building
• Using expatpp library in your project
  • The "Hello World" example
  • Approach #1: Use Cmake's FetchContent() Command
  • Approach #2: Install libexpatpp library on machine.
  • Approach #3: Use as git submodule and use cmake in your project via CMake.
• documentation
• tests
• - generate C++ code from xsd files
• Examples
  • - parse doxygen xml output
• and contributing
• Publication
• Acknowledgements

Overview

A lightweight and modern C/C++ library for building xml parsers.

Currently a work in progress.

Features

• wraps and build expat as part of library
• runs on all major platforms: Windows, OSX, linux
• provides an easy to use delegate class to build xml parsers
• [WORK IN PROGRESS]utilizing lambda for easy adding of handler callbacks
• [WORK IN PROGRESS]provides implementation of parser with stack of parsestates
• [WORK IN PROGRESS]xsdgen for generating C++ classes and parser from xsd schemata

Building

libexpatpp can be built with CMake. CMake is able to produce a build environment for most platforms. For the most important IDE exists a generator option which allows to build project files for these systems.

The simplest (and platform independent) way to build the project using cmake is executing the following command:

cmake -B <builddir> && cmake --build <builddir>

First command in chain creates the build directory <builddir> and configures the project. Second command does a build of the default target in <builddir>.

Cmake can also be called with predefined options, here for configuring and building a Release build:

cmake -D CMAKE_BUILD_TYPE=Release -B <builddir> && cmake --build <builddir>

Using expatpp library in your project

The "Hello World" example

The example hello_world contains a complete sample project using libexpatcpp and makes use of Cmake's FetchContent() Command to include, build and link expatpp library(explained more detailed in Approach #1: Use Cmake's FetchContent() Command .

Our "hello_world" project has just one source file, hello_world.cpp file, and it looks like this:

 
#include <iostream>
#include "expatpp.hpp"
 
using std::cout;
using std::endl;
 
class element_delegate : public xmlpp::abstract_delegate {
public:
  std::string fullname;
  std::string characterData;
 
  void onStartElement( const XML_Char *fullname, const XML_Char **atts) override {
    this->fullname = fullname;
  }
 
  void onCharacterData(const char *pBuf, int len) override {
    characterData.append(pBuf,len);
  }
};
 
int main(int argc,char** argv) {
  // prepare xml input, 
  const char* xml = "<p>hello world!</p>";
 
  // use the delegate to extract character data from input string
  element_delegate d;
 
  // parse xml input using delegate d's callbacks
  xmlpp::parser::result res = xmlpp::parser::parseString(xml,d);
 
  switch(res) {
 
  case xmlpp::parser::result::OK:
    // and output the extracted data in case of successful parsing
    cout << "element " << d.fullname << endl
     << " contains this text: "<< d.characterData << endl;
    return EXIT_SUCCESS;
 
  default:
    cout << "error " << static_cast<int>(res)
     << " on parsing " << endl;
    return -static_cast<int>(res);
  }
}

Running it should output

element p
contains this text: Hello World

for the CMake based build we have included a simple CMakeLists.txt:

cmake_minimum_required(VERSION 3.1.3)
 
enable_language(C)
enable_language(CXX)
set(CMAKE_CXX_STANDARD 11)
 
if(POLICY CMP0077)
    cmake_policy(SET CMP0077 NEW)
endif()
 
project(expatpp_hello_world VERSION 0.0.1 LANGUAGES CXX)
 
include(FetchContent)
#
# expatpp Configuration variables
#
set(EXPATPP_BUILD_EXAMPLES Off)
set(EXPATPP_BUILD_TOOLS Off)
set(EXPATPP_BUILD_TESTS Off)
set(EXPATPP_BUILD_DOCS Off)
 
# add expatpp project to the build
FetchContent_Declare(expatpp
         GIT_REPOSITORY https://github.com/gittiver/libexpatpp.git
         GIT_TAG main
         )
 
if(NOT expatpp_POPULATED)
  FetchContent_Populate(expatpp)
  add_subdirectory(${expatpp_SOURCE_DIR} ${expatpp_BINARY_DIR})
endif(NOT expatpp_POPULATED)
 
# add executable
add_executable(hello_world hello_world.cpp)
 
# link against expatpp library (produced by expatpp)
target_link_libraries(hello_world PUBLIC expatpp)

To get you started quickly, let's take a look at a few ways to get simple Hello World project working.

Approach #1: Use Cmake's FetchContent() Command

CMake contains the FetchContent() command to use libraries where a project depends on.

With:

FetchContent_Declare(expatpp         
    GIT_REPOSITORY "https://github.com/gittiver/libexpatpp" 
    GIT_TAG "v0_0_1" )
FetchContent_MakeAvailable(expatpp)

we include the library into the build.

With:

target_link_libraries(your_exe expatpp)

we link our executable against libexpatpp. This approach is used in the helloworld example, you can use the CMakeFile.lst from there as starting point for your project.

Approach #2: Install libexpatpp library on machine.

You can install libraries by running in libexpatpp directory:

cmake --build <builddir> --target install

Now, all you have to do to compile your project is c++ helloWorld.cpp -o helloWorld -llibexpatpp.

If you get error message like cannot open shared object file: No such file or directory, make sure that your linker includes path where libexpatpp was installed.

Approach #3: Use as git submodule and use cmake in your project via CMake.

If you are using CMake for compilation, we suggest adding libexpatpp as a git submodule with the command

git submodule add https://github.com/gittiver/libexpatpp vendor/libexpatpp`

Afterwards, modify your top level CMakeLists.txt file accordingly:

add_subdirectory(vendor/libexpatpp EXCLUDE_FROM_ALL)
target_link_libraries(your_exe expatpp)

The add_subdirectory command adds a folder to the build tree, meaning it will run CMakeLists.txt from the included folder as well. Flag EXCLUDE_FROM_ALL disables building (and instalment) of targets in the added folder which are not needed in your project. In the above example only the (static) library libexpatpp will be build, while libexpatpp-aligner, hello_world and the rest won't. In order to access the libexpatpp API, add #include "expatpp.hpp" in your source file (CMake will automatically update your include path).

documentation

For complete documentation of libexpatpp library API, visit http://gittiver.github.io/libexpatpp (should be updated to the latest release).

To generate the latest API documentation yourself from the source, you need to have doxygen installed. Position yourself in the root directory and run doxygen, this will generate docs/ directory. Then open docs/html/index.html file with you favorite browser.

tests

- generate C++ code from xsd files

parses xml schemata and generates C++ code for types and elements from schema [TODO] generate also parser class for parsing schema

Examples

- parse doxygen xml output

the example parses the xml output of doxygen documentation system and does a simple listing of its elements on standard output.

and contributing

Feel free to send pull requests and raise issues.

When developing, you may want to use -D CMAKE_BUILD_TYPE=Debug flag when calling cmake in order to get debugging flags passed to compiler. This should also happen if you just run cmake .. with no flags, but I think I have noticed it does not always works as expected (probably has something to do with cmake cache). To check which flags is compiler using, run make with VERBOSE=1: make VERBOSE=1.

Publication

Acknowledgements