plugin.h File Reference

Simplify 'plugin' classes to be discovered and/or loaded at runtime. More...

#include <openbabel/babelconfig.h>
#include <openbabel/dlhandler.h>
#include <string>
#include <iostream>
#include <vector>
#include <map>
#include <sstream>
#include <cstring>
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struct  CharPtrLess
 Case insensitive string comparison for PluginMapType key. More...
class  OBPlugin
 Base class for all types of dynamic classes discovered at runtime. More...


namespace  OpenBabel


#define MAKE_PLUGIN(BaseClass)
#define OB_STATIC_PLUGIN(className, instanceName)


std::vector< std::string > EnableStaticPlugins ()

Detailed Description

Simplify 'plugin' classes to be discovered and/or loaded at runtime.

The code in this file makes it easy to make 'plugin' classes. These classes are derived from a base class, like OBFingerprint. The derived classes ('sub-types' like fingerprint2) usually have a single instance. Plugin classes are only discovered at runtime, so no existing code needs to be changed when adding a new derived class. In some builds the new code can be added or removed by just moving a DLL or so file. The plugin classes derived from any base class (including new ones) type can be listed from the commandline.

Step-by-Step Instructions

1) In the header file for YourBaseClass (which handles whatsits). Make sure to include the plugin.h header , derive the class from OBPlugin and in its definition add the MAKE_PLUGIN macro and a function TypeID() containing a simple descriptor of the type

#include <openbabel/plugin.h>
class YourBaseClass : public OBPlugin

  const char* TypeID()
  { return "whatsits"; }; of implementation, probably involving virtual functions redefined
  in the sub-type classes

See below for what the macro contains.

2) Declare each sub-type in a class derived from the base class and give it a constructor which calls OBPlugin constructor as shown:

class YourSubType1 : public YourBaseClass
  YourSubtype1(const char* ID, bool IsDefault=false)
    : YourBaseClass(ID, IsDefault){}

  virtual string Description()
  { return "A description with one or more lines";}; of implementation

Only the first line of the description is used when the subclasses are listed.

3) Declare a global instance of the sub-type class which specifies its ID. and, optionally, whether it is to be regarded as the default type of YourBaseClass.

YourSubType1 theType1("whatsit2",true);

4) The following functions are available:

YourBaseClass* YourBaseClass::FindType(const char* ID); This returns the default type when ID is NULL or empty.

To list the sub-types of any plugin class use the List which sends to cout by default (or any other ostream if specified).


The ListAsString and ListAsVector functions are alternatives, usable with scripting.

It is also possible to iterate through each sub-type by the following code:

  OBPlugin::PluginIterator itr;
    itr is a std::map::const_iterator
    itr->first is the ID of the subtype;
    itr->second is The OBPlugin* which you will have to cast to your type

Since this is not the most beautiful code, it is probably better to use the List methods if possible.

YourBaseClass* MakeNewInstance();

How it works

MAKE_PLUGIN(YourBaseClass) inserts the following code into YourBaseClass:


  //The collection of sub-types is in a local static variable to avoid
  //any difficulties with the order of initialization of static objects.
  static PluginMapType& Map()
    static PluginMapType m;
    return m;

  //Making the map accessible to the base class (Cannot be used during construction)
  virtual PluginMapType& GetMap()const
   return Map();

  static YourBaseClass*& Default()
    static YourBaseClass* d;
    return d;

  //Constructor registers the sub-type
  YourBaseClass(const char* ID, bool IsDefault=false)
    _id = ID;
    if(ID && *ID && *ID!=' ') //do not register if ID is empty or starts with a space
      if(IsDefault || Map().empty())
        Default() = this;
      //Ensure YourBaseClass is registered in OBPlugin so it can be accessed from the commandline
      PluginMap()[TypeID()] =this;

  static YourBaseClass* FindType(const char* ID)
    if(!ID || *ID==0)
      return Default();
    return static_cast<YourBaseClass*>(BaseFindType(Map(),ID));
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