使用C ++和嵌入式Mono调用C＃DLL时无法加载汇编系统

Question

I have a C# sample code which is compiled into DLL using xbuild on Linux, eg:

using System;
using System.IO;
using System.Collections.Generic;
// ...

namespace MySamples
{
public class MyExample
{
    public static void test()
    {
        SortedSet<int> ss = new SortedSet<int>();
    } 
    // main function calls for test()
}
}

I can easily compile the sample code in a command line using xbuild MyExample.csproj into exe or dll , and then run using mono MyExample.exe - everything works fine and the sample code returns an expected result.

Now I want to make a call for the sample code from my C++ code, in particular to the test() function. I'm using mono runtime for that, and this is my C++ code:

#include <mono/jit/jit.h>
#include <mono/metadata/object.h>
#include <mono/metadata/environment.h>
#include <mono/metadata/assembly.h>
#include <mono/metadata/debug-helpers.h>
#include <mono/metadata/mono-config.h>

// ...
MonoDomain* domain = mono_jit_init("MyExample.dll");
MonoAssembly* assembly = mono_domain_assembly_open(domain, "MyExample.dll");
mono_config_parse("MyExample.dll.config");

// mono is not installed in default locations:
mono_set_dirs("mypath/lib/mono", "mypath/etc/mono");

MonoImage* image = mono_assembly_get_image(assembly);

MonoClass* klass = mono_class_from_name(image, "MySamples", "MyExample");
MonoObject* object = mono_object_new(domain, klass);
mono_runtime_object_init(object);

// call test()
MonoMethodDesc* mdesc = mono_method_desc_new(":test()", false);
MonoMethod* method = mono_method_desc_search_in_class(mdesc, klass);
mono_runtime_invoke(method, object, NULL, NULL);

// shutdown the runtime
mono_jit_cleanup (domain);

The C++ code, when run, returns an error of type:

Unhandled Exception: System.IO.FileNotFoundException: Could not load file or assembly 'System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=...' or one of its dependencies. ...

Since I know that if I run the same code using mono through the command line and it works, I feel like there is a problem with my C++ code and how I set up the mono runtime. I fixed a bunch of other errors by adding mono_set_dirs since my Mono is not installed into the default directory (it's built from source).

I'm on Ubuntu 16.04, if it matters, mono is built from source, CMake is used to compile my C++ code, and the MyExample.dll.config content:

<configuration>
    <startup> 
        <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.6.1" />
    </startup>    
</configuration>

The *.csproj file include System in the following manner:

<Reference Include="System" />

Once again, I'm able to run the test() when using mono from command line (not from C++ project) with the C# settings as they are now.

Here is one more strange thing : if I replace the SortedSet<int> with List<int> , it runs without throwing any errors. How can it be? - they belong to the same namespace . I checked other types, and when initializing most of them, an exception gets thrown.

Any ideas what is wrong here? I've been checking the mono embedded docs to try to find what could be wrong with my set up, but this is as far as I can reach. I'm beginner with C#, mono runtime and embedded mono.

Answer 1

The problem was so trivial - I messed up the mono lib path in my C++ code. Apparently, you need to provide a prefix, and not the full path. So, in my case, I had to use:

mono_set_dirs("mypath/lib", "mypath/etc");

without using mono at the end.