UE 4/5 Crashes, Hello World in Third Party Library integration, EXCEPTION_ACCESS_VIOLATION

snook91 · June 14, 2022, 10:12am

Hello All !

I’m fighting with a EXCEPTION_ACCESS_VIOLATION when trying to integrate an Hello World string from a Third Party C++ Library. The strange thing is that the error does not happen every time.

The first time I run the game, everything works (but not every time). The second time I usually have less luck and Unreal Engine crashes.

The first time, usually it works.
Capture ok

The second time, usually it crashes.

Here, you will find the UE log file:

[2022.06.14-09.42.33:104][773]LogMaterial: Error: MaterialInstance "M_HLOD0_OpenWorld_MainGrid_L1_X-1_Y0_DL0LandscapeStreamingProxy_D7T4VF4LBP34PHV9XOEVM5TIG_1_2_5_0" parameter 'NormalTexture' assigned texture "HLOD0_OpenWorld_MainGrid_L1_X-1_Y0_DL0T_LandscapeStreamingProxy_D7T4VF4LBP34PHV9XOEVM5TIG_1_2_5_0_Normal" requires non-virtual texture

[2022.06.14-09.42.33:104][773]LogStreaming: Display: FlushAsyncLoading: 48 QueuedPackages, 0 AsyncPackages

[2022.06.14-09.42.34:387][773]LogWindows: Error: === Critical error: ===

[2022.06.14-09.42.34:387][773]LogWindows: Error:

[2022.06.14-09.42.34:387][773]LogWindows: Error: Fatal error!

[2022.06.14-09.42.34:387][773]LogWindows: Error:

[2022.06.14-09.42.34:387][773]LogWindows: Error: Unhandled Exception: EXCEPTION_ACCESS_VIOLATION reading address 0x0000020820800070

[2022.06.14-09.42.34:387][773]LogWindows: Error:

[2022.06.14-09.42.34:387][773]LogWindows: Error: [Callstack] 0x00007ffb02de2f4b UnrealEditor-Core.dll!UnknownFunction []

[2022.06.14-09.42.34:387][773]LogWindows: Error: [Callstack] 0x00007ffb0282a57c UnrealEditor-Core.dll!UnknownFunction []

[2022.06.14-09.42.34:387][773]LogWindows: Error: [Callstack] 0x00007ffac16a1ea1 UnrealEditor-LibBonjour.dll!ABonjourActor::BeginPlay() [C:\Users\moi\Documents\Developpements\UE5\TestExternalLibrary\Plugins\LibBonjour\Source\LibBonjour\Private\BonjourActor.cpp:20]

[2022.06.14-09.42.34:387][773]LogWindows: Error: [Callstack] 0x00007ffb03d14e3f UnrealEditor-Engine.dll!UnknownFunction []

[2022.06.14-09.42.34:387][773]LogWindows: Error: [Callstack] 0x00007ffb05b0ec92 UnrealEditor-Engine.dll!UnknownFunction []

[2022.06.14-09.42.34:387][773]LogWindows: Error: [Callstack] 0x00007ffb04649e21 UnrealEditor-Engine.dll!UnknownFunction []

[2022.06.14-09.42.34:387][773]LogWindows: Error: [Callstack] 0x00007ffb05a38238 UnrealEditor-Engine.dll!UnknownFunction []

[2022.06.14-09.42.34:387][773]LogWindows: Error: [Callstack] 0x00007ffb04604725 UnrealEditor-Engine.dll!UnknownFunction []

[2022.06.14-09.42.34:387][773]LogWindows: Error: [Callstack] 0x00007ffb00b49898 UnrealEditor-UnrealEd.dll!UnknownFunction []

[2022.06.14-09.42.34:387][773]LogWindows: Error: [Callstack] 0x00007ffb00b7ec66 UnrealEditor-UnrealEd.dll!UnknownFunction []

[2022.06.14-09.42.34:387][773]LogWindows: Error: [Callstack] 0x00007ffb00b4a342 UnrealEditor-UnrealEd.dll!UnknownFunction []

[2022.06.14-09.42.34:387][773]LogWindows: Error: [Callstack] 0x00007ffb00b9d42a UnrealEditor-UnrealEd.dll!UnknownFunction []

[2022.06.14-09.42.34:387][773]LogWindows: Error: [Callstack] 0x00007ffb00ba0c37 UnrealEditor-UnrealEd.dll!UnknownFunction []

[2022.06.14-09.42.34:387][773]LogWindows: Error: [Callstack] 0x00007ffb00ba0521 UnrealEditor-UnrealEd.dll!UnknownFunction []

[2022.06.14-09.42.34:387][773]LogWindows: Error: [Callstack] 0x00007ffb0053dcb3 UnrealEditor-UnrealEd.dll!UnknownFunction []

[2022.06.14-09.42.34:387][773]LogWindows: Error: [Callstack] 0x00007ffb00eca666 UnrealEditor-UnrealEd.dll!UnknownFunction []

[2022.06.14-09.42.34:387][773]LogWindows: Error: [Callstack] 0x00007ff6d0a282f6 UnrealEditor.exe!UnknownFunction []

[2022.06.14-09.42.34:387][773]LogWindows: Error: [Callstack] 0x00007ff6d0a40d9c UnrealEditor.exe!UnknownFunction []

[2022.06.14-09.42.34:387][773]LogWindows: Error: [Callstack] 0x00007ff6d0a40e8a UnrealEditor.exe!UnknownFunction []

[2022.06.14-09.42.34:387][773]LogWindows: Error: [Callstack] 0x00007ff6d0a43c4d UnrealEditor.exe!UnknownFunction []

[2022.06.14-09.42.34:387][773]LogWindows: Error: [Callstack] 0x00007ff6d0a55564 UnrealEditor.exe!UnknownFunction []

[2022.06.14-09.42.34:387][773]LogWindows: Error: [Callstack] 0x00007ff6d0a58736 UnrealEditor.exe!UnknownFunction []

[2022.06.14-09.42.34:387][773]LogWindows: Error: [Callstack] 0x00007ffbb8397034 KERNEL32.DLL!UnknownFunction []

[2022.06.14-09.42.34:387][773]LogWindows: Error: [Callstack] 0x00007ffbb9b22651 ntdll.dll!UnknownFunction []

[2022.06.14-09.42.34:387][773]LogWindows: Error:

[2022.06.14-09.42.34:399][773]LogExit: Executing StaticShutdownAfterError

[2022.06.14-09.42.34:400][773]LogWindows: FPlatformMisc::RequestExit(1)

[2022.06.14-09.42.34:400][773]LogWindows: FPlatformMisc::RequestExitWithStatus(1, 3)

[2022.06.14-09.42.34:400][773]LogCore: Engine exit requested (reason: Win RequestExit)

[2022.06.14-09.42.34:406][773]Log file closed, 06/14/22 11:42:34

My Project is a blank C++ project.

I created a blank Third Party Plugin (from the Plugin menu) and added a SayHello() function in the ExampleLibrary files, like this:

// ExampleLibrary.h
#if defined _WIN32 || defined _WIN64
#define EXAMPLELIBRARY_IMPORT __declspec(dllimport)
#elif defined __linux__
#define EXAMPLELIBRARY_IMPORT __attribute__((visibility("default")))
#else
#define EXAMPLELIBRARY_IMPORT
#endif
#include <string>

EXAMPLELIBRARY_IMPORT void ExampleLibraryFunction();
EXAMPLELIBRARY_IMPORT std::string SayHelloFromLib();

// ExampleLibrary.cpp
#if defined _WIN32 || defined _WIN64
    #include <Windows.h>

    #define EXAMPLELIBRARY_EXPORT __declspec(dllexport)
#else
    #include <stdio.h>
#endif

#ifndef EXAMPLELIBRARY_EXPORT
    #define EXAMPLELIBRARY_EXPORT
#endif
#include <string>

EXAMPLELIBRARY_EXPORT void ExampleLibraryFunction()
{
#if defined _WIN32 || defined _WIN64
	MessageBox(NULL, TEXT("ExampleLibrary.dll chargée depuis le Plugin Third Party."), TEXT("Third Party Plugin"), MB_OK);
#else
    printf("ExampleLibrary.dll chargée depuis le Plugin Third Party.");
#endif
}

EXAMPLELIBRARY_EXPORT std::string SayHelloFromLib() {
    return "Bonjour depuis la librairie externe !";
}

The SayHello function just returns a std:string.

I created an Actor in my plugin with UE and I edited the BeginPlay function:

// BonjourActor.cpp
void ABonjourActor::BeginPlay()
{
	Super::BeginPlay();

	FString Message = FString(UTF8_TO_TCHAR(SayHelloFromLib().c_str()));	
	GEngine->AddOnScreenDebugMessage(-1, 10.0, FColor::White, Message);
}

Here, you will find my *.Build.cs files:

// TestExternalLibrary.Build.cs (the Build.cs of the UE Project)
public class TestExternalLibrary : ModuleRules
{
	public TestExternalLibrary(ReadOnlyTargetRules Target) : base(Target)
	{
		PCHUsage = PCHUsageMode.UseExplicitOrSharedPCHs;
	
		PublicDependencyModuleNames.AddRange(new string[] { "Core", "CoreUObject", "Engine", "InputCore", "LibBonjour" });

		PrivateDependencyModuleNames.AddRange(new string[] { });
	}
}

// LibBonjour.Build.cs (the Build.cs of the UE Plugin)
PublicDependencyModuleNames.AddRange(
			new string[]
			{
				"Core",
				"LibBonjourLibrary",
				"Projects",
				"Engine",
				"CoreUObject"
				// ... add other public dependencies that you statically link with here ...
			}
			);

// LibBonjourLibrary.Build.cs (the Build.cs of the third party library)
if (Target.Platform == UnrealTargetPlatform.Win64)
		{
			// Add the import library
			PublicAdditionalLibraries.Add(Path.Combine(ModuleDirectory, "x64", "Release", "ExampleLibrary.lib"));

			// Delay-load the DLL, so we can load it from the right place first
			PublicDelayLoadDLLs.Add("ExampleLibrary.dll");

			// Ensure that the DLL is staged along with the executable
			RuntimeDependencies.Add("$(PluginDir)/Binaries/ThirdParty/LibBonjourLibrary/Win64/ExampleLibrary.dll");
        }
        else if (Target.Platform == UnrealTargetPlatform.Mac)
        {
            PublicDelayLoadDLLs.Add(Path.Combine(ModuleDirectory, "Mac", "Release", "libExampleLibrary.dylib"));
            RuntimeDependencies.Add("$(PluginDir)/Source/ThirdParty/LibBonjourLibrary/Mac/Release/libExampleLibrary.dylib");
        }
        else if (Target.Platform == UnrealTargetPlatform.Linux)
		{
			string ExampleSoPath = Path.Combine("$(PluginDir)", "Binaries", "ThirdParty", "LibBonjourLibrary", "Linux", "x86_64-unknown-linux-gnu", "libExampleLibrary.so");
			PublicAdditionalLibraries.Add(ExampleSoPath);
			PublicDelayLoadDLLs.Add(ExampleSoPath);
			RuntimeDependencies.Add(ExampleSoPath);
		}

I will be delighted if anyone could help me with this problem. I’m looking for a solution since few days and I really need some support.

Thank you in advance.

Regards.

dorusoftware · June 14, 2022, 10:31am

maybe that library is just faulty, has some errors inside and doesn’t work properly

snook91 · June 14, 2022, 10:37am

Hello dorusoftware,

Thanks for your help.
The library I use is just a function which returns an std::string. You can see the code of this library above (ExampleLibrary.h/.cpp).

...
EXAMPLELIBRARY_EXPORT std::string SayHelloFromLib() {
    return "Bonjour depuis la librairie externe !";
}
...

I have recompiled this library many times. It comes from the Unreal Engine template provided. I have just added the SayHelloFromLib function.

dorusoftware · June 14, 2022, 10:50am

I don’t know much about programming so not the best user to help you.

One hint I could give that maybe is related is to use the engine implementation of the data types.

so instead of using the c++ data types like string use FString

snook91 · June 14, 2022, 12:07pm

Thanks for the link. But, the goal is to link with an external library which is written in standard c++ (it’s the feature of the third party library template provided by Epic Games).

snook91 · June 20, 2022, 3:09pm

I’ve found the solution.

It’s due to a non standard stl c++ library implementation ( Why doesn’t UE utilize STL containers? - Programming & Scripting / C++ - Unreal Engine Forums).
So, I must not use std::string in my DLL interface (ExampleLibrary.h) and must replace it by:

EXAMPLELIBRARY_IMPORT char * SayHelloFromLib();