CAn any one tell me about DLL files?

Question

DLL files in C, C++ or any other language Ho can we create it?

Answer 1

DLL stands for Dynamic Link Libraries.

They are platform independent files.

They can be created in other langugaes and used by other application/languages

VC++, VB 5/6 had great capabilities to create DLL quickly.



in VC++ and VB, the IDE has an option to compline a code as DLL, coding style is same as any other code you write.



It can also be defined as



1) Short for Dynamic Link Library, a library of executable functions or data that can be used by a Windows application. Typically, a DLL provides one or more particular functions and a program accesses the functions by creating either a static or dynamic link to the DLL. A static link remains constant during program execution while a dynamic link is created by the program as needed. DLLs can also contain just data. DLL files usually end with the extension .dll,.exe., drv, or .fon.



A DLL can be used by several applications at the same time. Some DLLs are provided with the Windows operating system and available for any Windows application. Other DLLs are written for a particular application and are loaded with the application.





2) Short for Delay Locked Loop, Delay-Locked Loop (DLL) supports high-bandwidth data rates between devices. These DLLs are circuits that provide zero propagation delay, low-clock skew between output clock signals throughout a device, and advanced clock domain control. These dedicated DLLs can be used to implement several circuits that improve and simplify system level design.





you can also GOOGLE what is DLL ? you will get hell lots of info about DLL..



Now a days DLL concept is considered as old this has been replaced by WEB SERVICES and XML.

Answer 2

While you're at it, look up DLL Hell: http://en.wikipedia.org/wiki/DLL_hell



Web Services and XML/XSL are the "newer" trendy phrases that are being used now. As far as I can tell, these trends have been used mainstream for roughly 5 years, until something better comes along.



DLL's are often used in classic asp/VB6/Older code as "COM" objects- http://en.wikipedia.org/wiki/Component_Object_Model. "COM" objects are basically when you take VB6 code, push it to "DLL", install that DLL on the server as a "COM" Object using the Admin tab in Control Panel. Once it's been registered on the server, using classic asp or other vb6 projects, you can use that DLL to do things like sending emails easier (call the dll with a from, to, subject, body, attachment, etc).



DLL's are also created during compilation of .NET code and stored in Bin folder. They can be updated dynamically in other .NET projects (I forget what the heck that's called). These DLL's get called on the server side when you want to do fancy things like AJAX (using the AJAX Toolkit).



The moral of this story is, DLL's can get very confusing, very fast to "simplify" code.

Answer 3

Dynamic link library can be understood by looking at how it differs from a header file(look at the following figure):

HEADER FILE-->Collection of functions which are not compiled

DLL------>Collection of functions which are already compiled, thats



Header file+Source code---->COMPILER---->obj file

obj file+dll file---->LINKER----->exe file



I know to create DLL file only in VC++6.0.

1.Open vc++6.0

2.File->new

3.Select MFC application wizard(dll) option and select create after giving the name for project..

4.Click Finish button from wizard

5.Type the code in the TheApp class as follows(a function add(int a, int b):

extern "C" __declspec(dllexport)double firstadd(double a,double b)

{

return a+b;

}

6. Press F5 key, your dll file will be ready



to use the dll file:

1.Create a new project as before and choose MFC application wizard(exe)

2.in any header file type :

extern "C" __declspec(dllimport)double add(double a, double b);



3.Now u can call the add function in usual way anywhere in ur program.

4.press F5 to run...



The steps may not be clear if u havent worked with VC++ before..

But still i hope the concept of dll is clear..........