Importing outside DLLs into
.Net platform and using them
By
Anupama Atmakur
Overview
 What is a DLL ?
 Issues in using DLL :DLL hell.
 Subtle difference between a DLL and a dot net
assembly
 What is an assembly?
 How to create a DLL?
 How is a DLL imported into .net?
 Demo showing how to import a DLL into .net?
What is a DLL?
 “DLL” stands for dynamic-link library.
 It is an executable file that acts as a shared
library of functions.
 The executable code for the functions are
located in a DLL, which are compiled, linked,
and stored separately from the processes that
use them.
What makes it dynamic?
 DLL is a file that is loaded, and its functions
linked dynamically at run time.
 It allows an executable module to include only
the information needed to locate the
executable code for a DLL.
 Where as in static linking, the linker gets all of
the referenced functions from the static link
library and places it with in your code into your
executable.
Advantages…
Save memory and disk space.
Upgrade easier.
Provide after-market support.
Provide a mechanism to extend the MFC library
classes.
 Support Multilanguage programs
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DLL Hell problem using DLLs…
When a DLL is updated on a computer, the
older version is removed and replaced with the
newer version. If the new version is not
compatible with the previous version, this
usually crashes applications that use the
component.
Solution…
The .NET Framework provides support for sideby-side execution, which allows multiple
versions of an assembly to be installed on the
same computer, at the same time. As a result
managed applications can select which version
to use without affecting other applications that
use a different version.
Shift from DLL to Dot Net
Assemblies in Microsoft. NET
 DLL contains library code to be used by any
program running on Windows.
 Dot net assemblies are understandable to only
Microsoft. NET and can be used only in .NET
managed applications.
 Assemblies can maintain versioning with the
help of the manifest.
 Giving a Strong name to an assembly is a key
to avoid DLL Hell.
What is an assembly?
 Assemblies are the building blocks of .NET
Framework applications.
 They contain the definition of types, versioning
information for the type, meta-data, and
manifest.
 They form the fundamental unit of deployment,
version control, reuse and security
permissions.
How to create a DLL?
 A DLL can be created using the following
command line statements:
 Single-File:
csc /out:add.dll /target:library add.cs
 Multi-File:
• csc /out:samlemodule.netmodule
/target:module add.cs
• al /out:MultiFileAssembly.dll /target:library
samlemodule.netmodule
Using a DLL…
 Using command line statement
csc /target:library /reference:add.dll
program.cs
 Using GUI
Strong Name
 Shared assemblies must have a strong name
as it is a unique identifier of an assembly.
 A strong name consists of the assembly's
name, version and culture metadata, plus a
cryptographic public key and a digital
signature.
 Public key is used for validation.
•
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sn -k Keyfile.snk
This command creates a new pair of keys and stores
it in a filenamed Keyfile.snk.
Creating an Assembly Strong Name
The following attribute are added to the
AssemblyInfo.cs
using System.Reflection;
using System.Runtime.CompilerServices;
[assembly: AssemblyCulture(“en-us")]
[assembly: AssemblyVersion(“1.0.0.0")]
[assembly: AssemblyKeyFile(" Keyfile.snk")]
Sharing an Assembly: The Global
Assembly Cache
 Install an assembly in the GAC
gacutil /i mult.dll
 Remove the assembly from the GAC
gacutil /u math
Demo to secure a dll using a keyfile.
References
 http://msdn2.microsoft.com/enUS/library/3707x96z(VS.80).aspx
 http://support.microsoft.com/kb/81506
5
 http://www.codeproject.com/dll/The_DL
L_Hell.asp
Questions??