Dynamic Link Library (DLL)

Dynamic Link Library (DLL) is a module that contains methods and data that can be used by another module. In simple terms DLL file is used to make link between 2 files or sofwares. Inside visual studio we are having some templates that used to create .dll files. So far in the above articles we've done all our code inside Console App (.NET Framework) template. For the first time we going to use different template in visual studio called Class Library (.NET Framework). Open visual studio, click create new project, Now choose Class Library (.NET Framework) template.

Call by referrence or Reference type memory allocation

Class library (.NET Framework) template is not a executable template. Here we cannot compile the program like what we've done so far. Here we can only build the program. If we build the program a new .dll file will be generated inside bin - debug folder inside project's file location. Using that generated .dll file we can make a link between multiple projects. Once we create new project using class library template we'll not find any main method inside. we'll only find namespace with project name what we given.

CODE

EG 1 . Writing first DLL code.

namespace NewlyCreatedNamespace {
    public static class basicMath {
        public static double Deg2Rad(double degree) {
            return degree * Math.PI / 180;
        }
        public static double Rad2Deg(double radian) {
            return radian * 180 / Math.PI;
        }
    }
    namespace subNamespace1 {
        namespace space {
            public class rectangle {
                public double length, width, height;
                //Internal variable can only be accessed inside current class library project(It cannot be accessed outside this project).
                internal double sampleVariable;
                public double Area() {
                    return length * width;
                }
                public double Perimeter() {
                    return 2 * (length + width);
                }
                public double Volume() {
                    return Area() * height;
                }
            }
        }
    }
}

Once after writing above code inside class library project, go to the top menu where you will find an option called Build. Click Build then click Build Solution. Now a new dll file will be created inside bin - debug folder inside project's file location. We successfully generated our First dll file. Now we need to link that dll file to a different executable project. In order to do that, close current project. Create new project on Console App (.NET Framework) template. Once new project opened, Make sure you are having solution explorer window in the Right hand side. If not goto top menu click View - Solution Explorer. Now solution explorer window will be opened in RHS.
Inside solution explorer there is an option called References. Right click that References and click Add reference. Now Reference Manager window will open. Make sure you are under Browse tab in LHS. Bottom right of Reference Manager window will have a Browse button click that refer the memory location where we stored our generted dll file. Choose that dll and click OK. Now we made the link between dll file and current project, whatever code we written inside dll file can be now accessed inside current Console App project. All the other rules are same as that of what we studied in Namespace concept.


What is the use of DLL file?
The main advantage of using DLL file is modularization of code, code reuse, efficient memory usage, and reduced disk space. We can create one DLL file with frequently used classes and methods. From next time onwards if we need to use any method or class present inside dll, we can simply refer that file and use whatever code we written inside.

Exercises
1. Create a DLL file with the logics for all Loop exercises what given in While loop, For loop, Do While loop and foreach loop articles.

(Click Here, For more exercises)