Singleton Pattern in C Examples

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Singleton design pattern in C# is one of the most widely used design patterns. In this pattern, only one instance of a class is created

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JAVA, Servlet, Design Pattern

Why would we want to use a Singleton? In some programs you would want a single instance of a class, for example a db connection. If you have multiple connections you may have fall into update race proplems or lockups from multiple connections trying to gain access the same db. An implementation of the singleton pattern must: ensure that only one instance of the singleton class ever exists; and provide global access to that instance. Typically, this is done by declaring all constructors of the class to be private; and providing a static method that returns a reference to the instance. We start with createing a ‘Singleton’ class, a .cpp file. #include class Singleton { static Singleton* s; std::string onlyOne; Singleton(); public: Singleton(const Singleton\u0026) = delete; Singleton\u0026 operator=(const Singleton\u0026) = delete; ~Singleton(); static Singleton* getInstance(); void setSingleton(const std::string \u0026st); std::string getSingelton(); }; You need to disable the copy constructor. Now let’s create the .h Singleton header file. #include class Singleton { static Singleton* s; std::string onlyOne; Singleton(); public: Singleton(const Singleton\u0026) = delete; Singleton\u0026 operator=(const Singleton\u0026) = delete; ~Singleton(); static Singleton* getInstance(); void setSingleton(const std::string \u0026st); std::string getSingelton(); }; Now let’s put this all together in main method in the main.cpp file #include #include \

JAVA, Servlet, Design Pattern

Singleton design pattern, singleton pattern, singleton vs static class, why singleton is an anti-pattern, why singleton sealed, singleton vs transient

Padrões de Projetos

Introduction The example below are based on my need to hold and transfer two fields from LIKP. It is easy to expand to hold other table structures or single fields. The datastore could be used to replace the usage of MEMORY ID, which are not very readable / maintanable. A (very) short introduction for those who are not familiar with the singleton design pattern. The singleton design pattern ensures that
only one instance of the class is created. The class contains its own constructor, and in this method logic is placed that ensures the creation of only one instance. And now for the fun part. I have documented the code(!), so it should be readable with just screenshots. Class definition The class for the data store: And the O_DATA_STORE attribute: Constructor The constructor for the class is the GET_OBJECT method. Methods And two simple PUT and GET methods for the LIKP structure: Use of class The following is the test program that shows the datastore in use. First the main program: The next level in the call stack: And the last level of the call stack: Conclusion At this point the LIKP-VBELN contains the number 2. This show that our data store object are kept in memory the whole way through the call stack. Please note that if you leave the call stack (i.e. start another report), then you will loose the reference to the object. With this datastore class you can now avoid using MEMORY ID to store and move variables trough the call stack. Further enhancement After the initial build of the class I have enhanced it further, and changed the GET-methods with a return parameter to evaluate if the field has been stored. I also added a RESET-method. This method marks the field as unstored. This has the advantage of being able to check if the field have been initiated. And also to reset the field after it have been retrieved/used. METHOD put_berot. v_berot = i_berot. v_berot_initiated = abap_true. ENDMETHOD. METHOD reset_berot. v_berot = ”. v_berot_initiated = abap_false. ENDMETHOD. METHOD get_berot. e_berot = v_berot. r_berot_initiated = v_berot_initiated. ENDMETHOD.

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