Question

DLLs 101

Asked by: smmsmm57

I have a dll that I need to link against and that I do not have the source code for....it was supplied to me by someone whose source code I am not permitted to see.....

I am using Visual Studio 6. In order for me to be able to link and run against this dll I assume I need it in a folder that is in the search path of the IDE at build time and within a folder on the machine that I intend to have the executable run on as well. Is this true?

Is there anyway to "bundle" the dll within the executable itself or is the entire purpose of a dll to avoid doing exactly that.....

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Asked On
2009-11-06 at 08:14:53ID24878314
Tags

Dll Windows Prgramming C++

Topics

C Programming Language

,

Microsoft Visual C++.Net

Participating Experts
3
Points
500
Comments
5

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Answers

 

by: evilrixPosted on 2009-11-06 at 08:17:26ID: 25760439

Windows uses the following search paths to locate a DLL

- The directory where the executable module for the current process is located.
- The current directory.
- The Windows system directory. The GetSystemDirectory function retrieves the path of this directory.
- The Windows directory. The GetWindowsDirectory function retrieves the path of this directory.
- The directories listed in the PATH environment variable.

http://msdn.microsoft.com/en-us/library/7d83bc18.aspx

 

by: AndyAinscowPosted on 2009-11-06 at 08:23:29ID: 25760495

LoadLibrary
 
The LoadLibrary function maps the specified executable module into the  address space of the calling process.
For additional load options, use the LoadLibraryEx function. HMODULE LoadLibrary(
 LPCTSTR lpFileName
);
 Parameters lpFileName  [in] Pointer to a null-terminated string that names the executable module  (either a .dll or .exe file). The name specified is the file name of the module  and is not related to the name stored in the library module itself, as specified  by the LIBRARY keyword in the module-definition (.def) file.  
If the string specifies a path but the file does not exist in the specified  directory, the function fails. When specifying a path, be sure to use  backslashes (\), not forward slashes (/).
If the string does not specify a path, the function uses a standard search  strategy to find the file. See the Remarks for more information. Return Values
If the function succeeds, the return value is a handle to the module.
If the function fails, the return value is NULL. To get extended error  information, call GetLastError. Windows Me/98/95:  If you are using LoadLibrary to  load a module that contains a resource whose numeric identifier is greater than  0x7FFF, LoadLibrary fails. If you are attempting to load a 16-bit DLL  directly from 32-bit code, LoadLibrary fails. If you are attempting to  load a DLL whose subsystem version is greater than 4.0, LoadLibrary  fails. If your DllMain function tries to call  the Unicode version of a function, LoadLibrary fails.


There is more, including examples, in the help files.
Basically it can be in any directory you want it to be in - just supply the full path.

 

by: AndyAinscowPosted on 2009-11-06 at 08:24:41ID: 25760511

>>Is there anyway to "bundle" the dll within the executable itself or is the entire purpose of a dll to avoid doing exactly that.....

The purpose of the dll is to keep it separate from the exe (eg. code reuse - functions can be used by other exe's)

 

by: smmsmm57Posted on 2009-11-06 at 08:25:32ID: 25760520

OK...thanks..... Officially, this is probably another question but let me ask here anyway....thanks for your answer I will give you points regardless.....

I see in VStudio 6 where I can specify what libs to link against but I do not see where I can specify what dlls to include as input to the linker? Or is it specified somnewhere else? Thanks

 

by: Anthony2000Posted on 2009-11-06 at 08:29:43ID: 25760554

There are two basic ways to use a DLL in your program.

1. You link your program to the creator's supplied .lib file. (this .lib file is supplied by whoever supplied the DLL and this is optional)

2. At run time you get a pointer to the function inside the DLL you want to execute and then call the function via a function pointer.

More info:

http://msdn.microsoft.com/en-us/library/ms683212%28VS.85%29.aspx

http://msdn.microsoft.com/en-us/library/ms682589%28VS.85%29.aspx


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