Plugin does not appear in Expression on client's Cinema 4D

yaya

@ferdinand hmm, now I think I understand.
Actually I had a problem last week with including these libcurl.dll and libcrypto-3-x64.dll into my VS2019 project. Even adding these .lib linking into the additional lib derectories and additional dependancies, I think I got the same error you quote above : Could not load libcurl.dll, libcrypto-3-x64.dll.
And only the manually adding these tow dlls into Windows/System32 fixed that problems.

So now after your explanation I understand that I did not make everything correctly.

The question is now: how to properly add the
\curl_x64-windows\debug\lib
\openssl_x64-windows\debug\lib
libcurl-d.lib
libcrypto.lib
into a project (do not shipping the exact .dlls with a plugin to clients)?...

ferdinand

Hey @yaya,

first of all, I must remind you of our support rules:

We cannot provide support for third party libraries.

We cannot debug your code for you and instead provide answers to specific problems.

The files you list there are all static libraries, at least when judging them by their extension *.lib. You would not have to ship them, as they are compiled into your app. Cinema 4D complains about missing dynamic libraries, e.g., libcurl.dll, heavily implying that your plugin tries to dynamically link against something.

The very popular libcurl library is offered in more flavors than there are atoms in the universe. I have no idea which one you used and what its details are. There are both statically and dynamically linking versions of libcurl. I cannot help you much with third party libraries and how to use them.

If I were you, I would do this:

Search for the two DLLs libcurl.dll and libcrypto-3-x64.dll on your system.
When you find them (and make sure to find all of them) note down the path where you found them, and rename the files, changing both extension and name, e.g., libcurl.dll -> foo.bar. I think this should be enough to hide them from the link loader of Windows (but I am not 100% sure).
Reboot your OS.
Boot Cinema 4D with -g_console, you should now see the same error as shown above.
Throw the two DLL into your plugin folder, e.g., into res/libs and boot again. Your plugin should work again.
Reestablish the DLLs in the paths where you found them, because when they are on your machine, there is a good chance some app is using them and might require exactly that version placed in that path.

Cheers,
Ferdinand

PS: When you still run into issues, please show us projectdefintion.txt of your project (the one from the module, e.g., root/plugins/ragdoll-plugin/project/projectdefintion.txt).

ferdinand

PS: Also try placing the DLLs in the root of your plugin folder, e.g., ragdoll_2025/libcurl.dll right next to the ragdoll_2025.xdl64, as I am not sure if you need extra settings for the res/libs path to work.

yaya

Hmm, after delete libcurl.dll, libcrypto-3-x64.dll, libcurl-d.dll from Windows/System32 I can't reproduce the problem on my side ("Error loading file:// Could not load libcurl.dll ...Could not load libcrypto-3-x64.dll"). The plugin still loads...
I understand that it is my problem, and you do not provide help with 3rd party libraries.
Just was dreaming that I will fix everything quickly.
Just delete libcurl.dll, libcrypto-3-x64.dll, libcurl-d.dll from Windows/System32 (where I've put them before), check if the same problem appears (the plugin does not loading), then put these files into res/libs.
But it turned out that I delete files, but the plugin still loads

I'll dig further...

yaya

Actually I am not fully correct: the plugin now does not loading in C4D r23 and C4D 2024. But still appears in C4D 2025
Frustrating...

Havremunken

One thing you could do is run a utility like procmon: https://learn.microsoft.com/en-us/sysinternals/downloads/procmon

This will let you see what a process accesses on the file system, among other things. Hopefully it will also show you which paths are searched for these libraries, allowing you to identify how to get them in the right location for your customer.

ferdinand

Hey @yaya,

When it still works, you likely missed some files somewhere. In the end you yourself can only untangle this, as we have no idea what you did there. I had a brief look at the main lib-curl project (there are many-many deviations), and what stands out, is that you also seem to have linked against the wrong library, at least judging by the main project.

[...] Could not load libcurl.dll due to Windows System Error #126 [...]

64 bit curl:

32 bit curl:

I.e., you seem to have linked against 32 bit curl, at least when judging by the name. This should not work in the first place, as Cinema 4D is a 64bit app, it cannot link against 32 bit DLLs (without getting very creative). What @Havremunken said would be the next logical step, use some of the debugging tools that come with Visual Studio. But it is of course not so good when you have to start reverse engineering your own app like that.

I assume you are all testing this on your development machine? I would recommend testing this on another machine, where you can be sure that it has not been 'tainted' with libcurl and other library fragments. When it still loads for you on such vanilla machine for you, than you have a real mystery on your hand, and have to start digging around deeper with some debug tools, to not only see what is failing (e.g., what is printed in the -g_console) but also which DLL access might succeed.

Cheers,
Ferdinand

yaya

I've managed to reproduce the problem: the Cinema does not load the plugin (r23 and 2025).
To do it, I not only deleted libcurl.dll, libcrypto-3-x64.dll, libcurl-d.dll from Windows/System32. It was enough for r23. For 2025 I was needed also to delete the variable from a PATH to Windows/System32.
Then I've tried to build the static lib of curl. I was thinking that this way will be better. I will not explain all the details, but it didn't - it just finished every build with:

1>LINK : fatal error LNK1104: cannot open file 'curl/libcurl_a_debug.lib'.

And nothing helped to fix that.
So I decided to return to the dynamic libraries. Actually I do not mind to supply the above dlls with my plugin.
I have reverted the binding to the dynamic version of curl and openSSL. Also I have added libcurl.dll, libcrypto-3-x64.dll, libcurl-d.dll to *plugin root/res/libs (not so hoping plugin will start to take them from there).
And I've delete the variable from a PATH (Windows/System32) to make sure it won't catch on these dlls from the System32.
Now I am making the build and it finishes with the success. And when I am starting the r23 - of course there is no plugin.
Yes, -g_console says:

WARNING: Error loading file:///H:/Code/r23/sdk/plugins/firstplugin/ragdoll.xdl64: Could not load dll because of
  Could not load libcrypto-3-x64.dll due to Windows System Error #126: The specified module could not be found. [win_dll.cpp(304)].
  Could not load libcurl-d.dll due to Windows System Error #126: The specified module could not be found. [win_dll.cpp(304)].. (file:///H:/Code/r23/sdk/plugins/firstplugin/ragdoll.xdl64) [win_dll.cpp(324)]
  Cause: Windows System Error #126: The specified module could not be found. [win_dll.cpp(318)] [general.cpp(401)]

Expected. The same problem which clients have.
(And yes, if I will back libcurl.dll, libcrypto-3-x64.dll, libcurl-d.dll to the System32, then my plugin appears in Expression)

So right now I need somehow to fix it so the plugin catch on libcurl.dll, libcrypto-3-x64.dll, libcurl-d.dll not from my Windows/System32 but from *res/libs.

How to do it?
DeepSeek gives me a hint that I can use

void SetDllSearchPath() {
    // Set the DLL search path to the res/libs folder
    SetDllDirectory(L"res\\libs");
}

// Call this function during plugin initialization
SetDllSearchPath();

But I am not sure is it right?
If it is not, then how to achieve this with maybe the other correct way?

ferdinand

Hey @yaya,

good to see that you made progress. To link against a static library, you can either set the respective Visual Studio module properties manually (not recommended) or set the relevant arguments in the projectdefitnion.txt of your module. For what you are doing, this could look something like this (for Windows), assuming curl would be situated in your project root, i.e., two folders "up".

AdditionalLibraryDirectories.Win64.Debug  =../../curl/bin/
AdditionalDependencies.Win64.Debug =libcurl_a_debug.lib
AdditionalIncludeDirectories=../../curl/include

FYI, you should not ship plugins using debug libraries, as they tend to be much-much slower than release code, due to all the debug symbols and other crap floating around in them, causing performance penalties of 10x, 20x, or even more.

Cheers,
Ferdinand

yaya

@ferdinand Yes, I will not ship the debug version of dlls. It is just for testing.
But are you sure that your that you wrote me right? Your hint is about the linking of static library but libcurl_a_debug.lib does not work for me.
Or did you mean that if I do as you described above it, the error 1>LINK : fatal error LNK1104: cannot open file 'curl/libcurl_a_debug.lib'. - will disappear? Then thank you about this solution, in this case I will need to get back again to a static library (which I already have deleted )
But what about the linking dlls to make libcurl.dll, libcrypto-3-x64.dll, libcurl-d.dll linked from res/libs during Cinema 4D startup (and for shipping first two to clients)? Is there some option for this?

ferdinand

Well, I answered this:

1>LINK : fatal error LNK1104: cannot open file 'curl/libcurl_a_debug.lib'.

Which is a linker error (the static linker at compile time), where the linker cannot find the static library (libcurl_a_debug.lib) to link against. I am quite frankly a bit in the unclear what you are trying to do exactly, use the statically or the dynamically linked version of your libraries. When you "just" want to load a DLL under Windows, you could do something like this:

#include <windows.h>
#include <iostream>

typedef void (*MyFunctionType)();

int main() {
    // Load the DLL
    HMODULE hModule = LoadLibrary(L"MyLibrary.dll");
    if (!hModule) {
        std::cerr << "Failed to load MyLibrary.dll" << std::endl;
        return 1;
    }

    // Get the function address
    MyFunctionType MyFunction = (MyFunctionType)GetProcAddress(hModule, "MyFunction");
    if (!MyFunction) {
        std::cerr << "Failed to get the function address" << std::endl;
        FreeLibrary(hModule);
        return 1;
    }

    // Call the function
    MyFunction();

    // Free the DLL
    FreeLibrary(hModule);

    return 0;
}

But doing all this low-level boilerplate code poking around has become somewhat unfashionable. And Visual Studio DLL projects or third party libraries usually offer two files when creating/shipping shared libraries. The actual shared library, e.g., MyLibrary.dll, and a static library file MyLibrary.lib which does not hold a static version of the library but the boilerplate code to correctly load that shared library at runtime and align the function/type pointers with symbols.

So, even when you dynamically link against a shared library at runtime, you often link statically against a library at compile time, which takes care of the runtime boilerplate code for you. What is the case for the libraries you used there, I have no idea. The settings in the projectdefinition.txt are just for static linking, as linkers/compilers do not care about dynamic linking.

Cheers,
Ferdinand

yaya

@ferdinand thank you for you answer.
I was thinking that:

if at the beginning (when I just started to add the curl and openSSL to a code) the code in the VS 2019 worked fine. But after making a build the plugin does not loaded in Cinema, throwing an error about missing dlls.

But, if I managed to fix it just via:

adding few dlls (libcurl.dll, libcrypto-3-x64.dll, libcurl-d.dll)
to Windows/System32 and by editing system variables...

...But in this case the plugin does not work on the client's side, because of:

clients do not have that dlls on their side,

Then:

I can "simply" make the plugin work on the client's side just (somehow) adding missing dlls => to a plugin's res/libs and shipping them with the plugin.

I was thinking it is easy to do. But if you say that it is not (or as I understand), then I will try your solution. Which seems harder for me because my lack of knowledges.
F.e. I did not understood how to set up an exact path in the projectdefitnion.txt via that command. If f.e. I have this text in the projectdefitnion.txt:

Platform=Win64;OSX
Type=Solution
Solution=\
	plugins/cinema4dsdk;\
	plugins/maxonsdk.module;\
	plugins/microsdk;\
	plugins/ragdoll

where the last line means the root folder of my plugin.
And if I need to include "curl" folder via your line:

AdditionalLibraryDirectories.Win64.Debug  =../../curl
AdditionalDependencies.Win64.Debug =libcurl_a_debug.lib
AdditionalIncludeDirectories=../../curl

where "curl" is a folder exactly in "ragdoll" and the "libcurl_a_debug.lib" is a file directly in the "curl"
So how to edit the line accordingly? I mean all that "../..." :

AdditionalLibraryDirectories.Win64.Debug  =../../curl

ferdinand

This:

Platform=Win64;OSX
Type=Solution
Solution=\
	plugins/cinema4dsdk;\
	plugins/maxonsdk.module;\
	plugins/microsdk;\
	plugins/ragdoll

is the projectdefitnion.txt of your solution, i.e., the build config which links all modules together. You must use plugins/ragdoll/project/projectdefitnion.txt instead, it is the build config for that module. Think of it as the CMakeLists.txt of that module when you are familiar with CMake. After these changes you must regenerate your project with the project tool.

I quite frankly do not understand your solution, but as always, whatever works, works. So, if it does work for you, I am happy.

The ".." in paths is common relative path syntax and means one folder up (in relation to the module). So, ../../foo means a foo folder in the root of your project.

root
  foo
  plugins
    ragdoll

Cheers,
Ferdinand

yaya

I know what is projectdefitnion.txt. I just do not understand how to use the line: AdditionalLibraryDirectories.Win64.Debug =../../curl
And do I need to launch again the buildsdk23.bat right after each time I change this file.
I have not added the static curl library in my project yet.

ferdinand

Well, you apparently do not, because you showed us the wrong projectdefitnion.txt file above, putting the command there won't work as I tried to explain And yes, you must regen your project after such changes, which I assume is what you mean with buildsdk23.bat.

yaya

Oh, you've edited your previous message! Thanks! I will try it.