DLL's

I was wondering if anyone has a tutorial on how to make DLL's for windows, (or possibly making DLL's for other OS's also) b/c my apartment complex burnt down yesterday and I lost all my books (Programming Windows 5th edition and about 30 other books) are all gone untill my stupid insurance pays off. So someone please help out a down and out code junkie.

Sorry to hear about your home.........that's terrible. Hope you get back on your feet soon.

Here's a small example I did for someone on the C++ board - here

Basically, all you are doing is creating functions and storing them outside of your program. You tell the compiler to export certain functions from the dll (see the #define DllExport extern "C" __declspec (dllexport) thing....then put DllExport in front of every exported function) and then it creates a dll file and a lib file. store that lib file in your main project.

Then declare the exported functions in the main project as you would for any normal forward declaration, but this time declare Macro in front of every decalaration as "#define DllImport extern "C" __declspec (dllimport)". Then prepend DllImport to every declaration. As long as the Dll is in the same Dir as your program (or one of the normal system dirs for a Dll), your program should run.

You should also try to stick to normal C for dlls......

Why should I stick to using C in a DLL? I was thinking about putting some classes into one, is this a bad idea? Thanks for the info so far.

The main problem is that funcs in C++ have name mangling issues (more than 1 name of a function so overloading can work)....therefore other languages choke as they cannot use these functions....

I add the "#define DllImport extern "C" to my dlls because I think that allows C to read them at the cost of operator overloading (I have never tested this though........)

If you are working in C++ exclusively, then you may be ok......

Well I generally dont use function overloading unless I really really really have to but usually I dont need to (other than constructors!). Can I put a class into a DLL? Sorry about all the questions but no place and all this stress has made me not tired and i want to code something on my rent's old pc which im on and let me tell you it sucks! It cant even run Quake2

Quote:

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Originally posted by xds4lx
Well I generally dont use function overloading unless I really really really have to but usually I dont need to (other than constructors!). Can I put a class into a DLL? Sorry about all the questions but no place and all this stress has made me not tired and i want to code something on my rent's old pc which im on and let me tell you it sucks! It cant even run Quake2

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Yeah, I guess, but to tell the truth I have not tried......

Ok im assuming that this will only work for Window's, is there any way to make DLL's that are cross platform? or does that require a totally different code layout?

I use Classes in DLL's all the time! It'z possible, but az he said, it's not good for thing'z made to be used in 'multi-language' stuff.

the 'DLL' concept itself i'z platform independant, but a 'DLL' file itself iz just 4 window'z, u can figure out the 'dll' type thing on that OS, and 'recompile'.

SPH

P.S., if doing classes, you will obviously need to exclude the "extern "C"" part!

So should I use extern "C++" instead?

If you're using a C++ Compiler, you're only using "extern "C"" to tell the compielr to compile in C for a section, you need not tell a C++ compiler to compile in C++! :)

Hope that answer'z ur Question, feal free to AIM me:

aGaBoOgAmOnGeR
Email/MSNIM: [email protected]

Thankx ~SPH

Whats the difference between __declspec (dllexport) and __declspec(dllimport) ?

dllimport imports symbolz (using the dll), dllexport exports (creating the dll).

SPH

Ok, well that doesnt seem clear enough, b/c in the source im looking at they give two examples of the same thing and they just say that __declspec(dllimport) just makes a little more efficient code and thats it. They use both dllimport and dllexport on the same function and i sure as hell dont see any difference. Also, is it better to just use the header you compiled the DLL with or write a new one w/ a different name?

Quote:

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Originally posted by xds4lx
Ok, well that doesnt seem clear enough, b/c in the source im looking at they give two examples of the same thing and they just say that __declspec(dllimport) just makes a little more efficient code and thats it. They use both dllimport and dllexport on the same function and i sure as hell dont see any difference.

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I think __declspec is a compiler command for VC++ that allows you to create dlls without having to create .def files (These files were to help the compiler know which functions to export).......I think its just a conveinience thing and its obvioiusly not part of the language.....worth putting in.

Quote:

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Also, is it better to just use the header you compiled the DLL with or write a new one w/ a different name?

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Sorry, I dont understand.

>>Also, is it better to just use the header you compiled the DLL with or write a new one w/ a different name?<<

I think you can use the same one if you use a #ifdef..#endif block to #define __declspec(dllimport) or __declspec(dllexport) depending on your requirements.
eg

Code:

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#if defined IMPORT_DLL
#define DLL_FN_THINGY __declspec(dllimport)
#else
#define DLL_FN_THINGY __declspec(dllexport)
#endif

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To use just #define IMPORT_DLL as required.

Here, this might be more user-friendly :) :

Code:

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#ifndef EXPORT
#define EXPORT __declspec(dllimport)
#endif//EXPORT

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That way, the User will never need to do anything :). When you u'ze it in the DLL, simple define EXPORT before you include the header, like this:

Code:

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#define EXPORT __declspec(dllexport)
#include "myheader.h"

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Tada! :)

SPH :p :) :p

Actually that can be a little better minime (same as Ken's but i already was using the EXPORT)

Code:

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#ifndef EXP
#define EXPORT __declspec(dllexport)
#elif !defined EXP
#define EXPORT __declspec(dllimport)

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Although for some reason VC likes to give a warning about redeclaration when using this to include the dll but whatever i just turn of those dumb warnings i know what im doing :D