Subj : Re: lib files
To   : comp.programming
From : Scott McPhillips [MVP]
Date : Sat Oct 08 2005 12:42 am

puzzlecracker wrote:
> Can someone provide an explanation for lib files that VS generates - I
> heard there are static and dynamic ones. How do they differ? what are
> pros and cons of each?
> 
> 
> Thanks
> 

A lib (for library) file contains previously compiled code, so you can 
easily include it in your program and call the functions it contains.

In the VS environment this classic definition of a lib file is a 
"static" lib file.  That means it actually contains the code, and when 
you link it in the code becomes part of your exe file.

A "dynamic" lib file is almost empty: It contains only stub functions 
that consist of a jump to someplace else, to be defined at run time.  It 
satisfies the linker's need to put a function address in your exe file, 
but the functions are empty.  The "someplace else" that actually 
contains the functions is a DLL (Dynamic Linking Library) file.  Every 
dynamic lib has a corresponding DLL.  Windows loads the DLL when your 
exe is loaded, and fixes up the jump addresses.

Pros of DLLs: Saves memory if more than one program uses the same 
functions.  Only one copy needs to be loaded into memory.  For example, 
the operating system is largely contained in DLLs shared by all running 
programs.  DLLs also provide a convenient way to divide programming work 
up into separate projects.  Programmer A can build and test his DLL 
without waiting for programmer B to fix some unrelated problem.

Cons of DLLs: Known as "DLL Hell," there can be version management 
problems.  Suppose your program relies on a Microsoft DLL.  Then 
Microsoft updates the DLL in some incompatible way, and some other 
program install brings in the new incompatible DLL file.  Your program dies.

-- 
Scott McPhillips [VC++ MVP]

.