# 7. Using the library

XML/Ada is a library. When compiling an application that uses it, you thus need to specify where the spec files are to be found, as well as where the libraries are installed.

There are several ways to do it:

- The simplest is to use the xmlada-config script, and let it provide the list of switches for gnatmake. This is more convenient on Unix systems, where you can simply compile your application with:

      gnatmake main.adb `xmlada-config`

  Note the use of backticks. This means that xmlada-config is first executed, and then the command line is replaced with the output of the script, thus finally executing something like:

      gnatmake main.adb -Iprefix/include/xmlada -largs -Lprefix/lib \\
        -lxmlada_input_sources -lxmlada_sax -lxmlada_unicode -lxmlada_dom

  Unfortunately, this behavior is not available on Windows (unless of course you use a Unix shell). The simplest in that case is to create a `Makefile`, to be used with the make command, and copy-paste the output of xmlada-config into it.

  xmlada-config has several switches that might be useful:

  - –sax: If you this flag, your application will not be linked against the DOM module. This might save some space, particularly if linking statically.
  - –static: Return the list of flags to use to link your application statically against Xml/Ada. Your application is then standalone, and you don’t need to distribute XMl/Ada at the same time.
  - –static_sax: Combines both of the above flags.

  If you are working on a big project, particularly one that includes sources in languages other than Ada, you generally have to run the three steps of the compilation process separately (compile, bind and then link). xmlada-config can also be used, provided you use one of the following switches:

  - –cflags: This returns the compiler flags only, to be used for instance with gcc.
  - –libs: This returns the linker flags only, to be used for instance with gnatlink.

  This xmlada-config method doesn’t provide access to the `xml_gtk` module, which is only available when using project files (see below).

- The preferred method, however, is to use the GNAT project files. See the GNAT user’s guide for more information on the project files and how to create them for your application.

  Basically, a project file contains the description of your build environment (source directories, object directories, libraries,...).

  The very simple case is when you have all your sources in the same directory (say `src/`), and the object files are all generated in the `obj/` directory.

  In this case, your project file would look like:

      with "xmlada";
      project Default is
         for Source_Dirs use ("src/");
         for Object_Dir use "obj/";
      end Default;

  and you build your application with:

      gprbuild -Pdefault main.adb

  Note in the project file the first line, which indicates that your application requires XML/Ada to build. This will automatically set the appropriate compiler and linker switches to use XML/Ada. Your application will be linker against all modules of XML/Ada (DOM, SAX, ...).

  If your application doesn’t use DOM, you can replace the first line with something like:

      with "xmlada_sax";

  which will reduce the number of libraries that your application is linked with.

  WHen you are using project files, you need to let GNAT know where to find the project files. This is done by setting the ADA_PROJECT_PATH environment variable, by adding to it the installation directory of XML/Ada, ie the one that contains xmlada.gpr

  If the installation prefix is the same as your GNAT installation, and you are using GNAT more recent than 5.03a, then it will automatically find XML/Ada’s project files.

  Check the `dom/test` directory in the XML/Ada package, which contains both code examples and project files that you can use as a basic for your own code.

The default type of library depends on the way you installed XML/Ada. In all cases, and assuming you installed both static and shared libraries, you can choose among the two by setting the environment variable:

    LIBRARY_TYPE=static

or:

    LIBRARY_TYPE=relocatable

Whatever method you used to build your application, you might have to change, at least one UNIX systems, the environment variable LD_LIBRARY_PATH so that it contains the `lib/` directory in the XML/Ada installation, so that the dynamic libraries are correctly found.

This is not needed if you build XML/Ada as a static directory.

## 7.1. Running on VxWorks

On VxWorks, XML Ada processing might require more stack space than what is typically available from the VxWorks shell, the tasks spawned from there with “sp”, or Ada tasks with no or a too small Storage_Size value attached.

Such stack overflow conditions are typically characterized by non-deterministic erratic behavior and can be cured by allocating more stack space for the tasks involved.