can anybody tell me what excatly ".dll " files? how it is created ?

Question

.dll (dynamic link library ) is one type of extension name i often see in my computer.I want to understand the cocept of these files

Answer 1

They are Frameworks or Library's developers use so they don't need to re-write the same code over and over again.

Answer 2

A .dll is a "dynamically linked library." It's a library of functions that other programs can call without being compiled together. So, I can can make a program that relies on some dll to be present and some function to be present even if it's not present to me when I create the program though you usually would want to try it out before deplying an app. Multiple programs can call functions within a dll. A dll is created just like any other program is created using a development application such as visual studio or java. Windows bases alot of it's functionality off of dll's.

Answer 3

Dynamic-link library (also written without the hyphen), or DLL, is Microsoft's implementation of the shared library concept in the Microsoft Windows and OS/2 operating systems. These libraries usually have the file extension DLL, OCX (for libraries containing ActiveX controls), or DRV (for legacy system drivers).

The file formats for DLLs are the same as for Windows EXE files — that is, Portable Executable (PE) for 32-bit Windows, and New Executable (NE) for 16-bit Windows. As with EXEs, DLLs can contain code, data, and resources, in any combination.

In the broader sense of the term, any data file with the same file format can be called a resource DLL. Examples of such DLLs include icon libraries, sometimes having the extension ICL, and font files, having the extensions FON and FOT.

In Win32, the DLL files are organized into sections. Each section has its own set of attributes, such as being writable or read-only, executable (for code) or non-executable (for data), and so on.

The code in a DLL is usually shared among all the processes that use the DLL; that is, they occupy a single place in physical memory, and do not take up space in the page file. If the physical memory occupied by a code section is to be reclaimed, its contents are discarded, and later reloaded directly from the DLL file as necessary.

In contrast to code sections, the data sections of a DLL are usually private; that is, each process using the DLL has its own copy of all the DLL's data. Optionally, data sections can be made shared, allowing inter-process communication via this shared memory area. However, because user restrictions do not apply to the use of shared DLL memory, this creates a security hole; namely, one process can corrupt the shared data, which will likely cause all other sharing processes to behave undesirably. For example, a process running under a guest account can in this way corrupt another process running under a privileged account. This is an important reason to avoid the use of shared sections in DLLs.

If a DLL is compressed by certain executable packers (e.g. UPX), all of its code sections are marked as read-and-write, and will be unshared. Read-and-write code sections, much like private data sections, are private to each process. Thus DLL's with shared data sections should not be compressed if they are intended to be used simultaneously by multiple programs, since each program instance would have to carry its own copy of the DLL, resulting in increased memory consumption.

Answer 4

A dynamic-link library (DLL) file is an executable file that allows programs to share code and other resources necessary to perform particular tasks. Microsoft Windows provides DLL files that contain functions and resources that allow Windows-based programs to operate in the Windows environment.

Answer 5

A .dll file is typically a driver for software and hardware. It is pretty much part of the instructions/map file to tell the software or hardware what to do.

Answer 6

Have a look at these sites if you want to learn more.
http://delphi.about.com/od/windowsshellapi/a/dll_basics.htm
http://www.flipcode.com/articles/article_creatingdlls.shtml