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Go to library to C# | BadImageFormatException

I would like to create a library out of go-code and use it inside a C# winforms project.
For the error scroll to the bottom.
Setup
GO 1.10.2
tdm-gcc-5.1.0-3
Windows 10 / x64
Go-project called exprt
What I've tried
I've created a minimal go-tool that creates a file in the working-dir:
package main
import (
"os"
"C"
)
func main() {
// nothing here
}
//export Test
func Test() {
os.OpenFile("created_file.txt", os.O_RDONLY|os.O_CREATE, 0666);
}
The next steps were taken from Building a dll with Go 1.7.
I've then compiled to c-archive with the following command: go build -buildmode=c-archive which gives me exprt.a and exprt.h.
After that I've created a file called goDLL.c (1:1 as in the link above) and inserted this code:
#include <stdio.h>
#include "exprt.h"
// force gcc to link in go runtime (may be a better solution than this)
void dummy() {
Test();
}
int main() {
}
Lastly I've run this command to create my final dll:
gcc -shared -pthread -o goDLL.dll goDLL.c exprt.a -lWinMM -lntdll -lWS2_32
which gave me "goDLL.dll".
My problem
In C# I've created a winforms-project with 1 button that calls this declared function (copied the dll to the debug-folder):
[DllImport("goDLL.dll")]
private static extern void Test();
Error
System.BadImageFormatException: "An attempt was made to load a program with an incorrect format. (HRESULT: 0x8007000B)"
Sorry for that big block of text but this was the most minimal test I could think off.
I appreciate every help in here.

Well, in the given answer here https://social.msdn.microsoft.com/Forums/vstudio/en-US/ee3df896-1d33-451b-a8a3-716294b44b2b/socket-programming-on-64bit-machine?forum=vclanguage there is written:
The implementation is in a file called ws2_32.dll and there are 32-bit and 64-bit versions of the DLL in 64-bit Windows.
So the build as described in my question is correct.
Solution
The C#-Project has to be explicitly set to x64. AnyCPU won't work and throw the error shown in the question above.
Everything is working now. I'm leaving the question and answer as this is a full explanation of how to get go-code running out of C#.

.net core - PInvoke C shared library function which depends on another shared library

I wrote some wrapper code for an existing library (wiringPi) to read a temperature sensor but ended up with an error while consuming this library.
My wrapper lib looks like:
mylib.h
#ifndef mylib_h__
#define mylib_h__
extern void read_sensor();
#endif
mylib.c
#include "mylib.h"
#include <wiringPi.h>
void read_sensor() {
//here is the first call on the wiringPi lib
if (wiringPiSetup() == -1)
exit(1);
...
}
then i use gcc to compile my library:
gcc -Wall -Werror -fPIC -c mylib.c
gcc -shared -o libmylib.so mylib.o -lwiringPi
cp libmylib.so /usr/lib/
Hint: In case of a normal C program consumption of this library everything works fine.
Now there‘s my C# program which use PInvoke to call read_sensor() from this library:
Program.cs
class Program
{
[DllImport("wiringPi")]
static extern int wiringPiSetup();
[DllImport("mylib")]
static extern void read_sensor();
static void Main(string[] args)
{
wiringPiSetup();
read_sensor();
}
}
This program is compiled with the following arguments:
dontet publish -r linux-arm
and copied to my Raspberry-Pi.
Now i execute this C# program and the following error is thrown:
./my-program-name: symbol lookup error: /usr/lib/libmylib.so: undefined symbol: wiringPiSetup
What‘s going wrong here?
My first thought was, my program didn‘t know the wiringPi library. So i added an export for this dll and called wiringPiSetup() for testing. Same result with or without this statement.
I added also a test function without the wiringPi dependency into my custom library. This is called fine by C#.
Did i mess something up at linking time?
Edit:
The command ldd /usr/lib/libmylib.so gives this output:
linux-vdso.so.1 (0x7efad000)
/usr/lib/arm-linux-gnueabihf/libarmmem.so (0x76f73000)
libwiringPi.so => /usr/local/lib/libwiringPi.so (0x76f40000)
libc.so.6 => /lib/arm-linux-gnueabihf/libc.so.6 (0x76dff000)
libm.so.6 => /lib/arm-linux-gnueabihf/libm.so.6 (0x76d84000)
libpthread.so.0 => /lib/arm-linux-gnueabihf/libpthread.so.0 (0x76d5c000)
librt.so.1 => /lib/arm-linux-gnueabihf/librt.so.1 (0x76d45000)
libcrypt.so.1 => /lib/arm-linux-gnueabihf/libcrypt.so.1 (0x76d05000)
/lib/ld-linux-armhf.so.3 (0x54abc000)

It comes down to name decoration. The C++ compiler doesn't just put the name of a function in the object file - it adds information to the name according to the function's definition (most notably its parameters).
From https://msdn.microsoft.com/en-us/library/56h2zst2.aspx
Functions, data, and objects in C and C++ programs are represented
internally by their decorated names. A decorated name is an encoded
string created by the compiler during compilation of an object, data,
or function definition. It records calling conventions, types,
function parameters and other information together with the name. This
name decoration, also known as name mangling, helps the linker find
the correct functions and objects when linking an executable.
But Compiled C code does not do this - name decorating (or name mangling) came in with C++.
So, you have to tell C# "this function's name is not decorated."
To do that use an attribute like this:
[DllImport("TestDll.dll", EntryPoint="myproc", ExactSpelling=false,CallingConvention=CallingConvention.Cdec‌​l)]
It's the "CallingConvention" bit that says "the function is a C function."
"Cdecl" means "C declaration", if I remember right.
More information can be found at: http://www.codeguru.com/csharp/csharp/cs_data/article.php/c4217/Calling-Unmanaged-Code-Part-1--simple-DLLImport.htm

pinvoke return a float

have been working on this for hours, couldn't get it work :(
below code gives exception "Attempted to read or write protected memory. This is often an indication that other memory is corrupt." this is fixed, see below update
but when i change the return type to int and return a int value, it works. how to make it to return a float value? thanks.
vs2012
c++ code
extern "C" __declspec(dllexport)
float compute_similarity()
{
return 1.01;
}
c# code
[DllImport("demo.exe", EntryPoint = "compute_similarity", CallingConvention = CallingConvention.Cdecl)]
public static extern float compute_similarity();
public void Get()
{
float x = compute_similarity(); // here returns random value
}
=====================================
UPDATE
See comments from David below, the problem was the c# project is targeting x64 and c++ is targeting Win32. After changing the c# project to target to x86, the exception went away.
However the call from c# returns some random value instead of 1.01 expected

I think your problem is that your function is declared in an executable rather than a DLL. Convert your native code into a library project and compile a DLL.
Your code will result in a call to LoadLibrary passing the file name demo.exe. The documentation for LoadLibrary says:
LoadLibrary can also be used to load other executable modules. For example, the function can specify an .exe file to get a handle that can be used in FindResource or LoadResource. However, do not use LoadLibrary to run an .exe file. Instead, use the CreateProcess function.
And so your code is doing exactly what you are told not to do. The call to LoadLibrary will succeed. The subsequent calls to GetProcAddress will succeed. But the module that you loaded is not fit to execute code.

BadImageFormatException error when using C++ .dll function for C#?

I am having trouble with using P/Invoke for C#. Here is the function (written in C++) that I am trying to call from the .dll:
string
BeatTracker::getName() const
{
return "Tempo and Beat Tracker";
}
And here is my code for trying to call this function:
[DllImport("qm-vamp-plugins.dll",EntryPoint="BeatTracker")]
public static extern string getName();
public QMTempo()
{
Console.WriteLine(getName());
}
What seems to be wrong? I am getting a BadImageFormatException. And how can I know what is wrong in future references aside from the vague names the IDE is giving me? I am using Visual Studio 2008 by the way.
Also I am using (but not sure if right) EntryPoint, to let it know that I am using the getName function from the BeatTracker class (because there are also getName functions for other classes, which are included in the single .dll file)
Thanks!

This exception can be caused by a mismath between the .NET runtime proc architecture used and the imported dll one.
More precisely:
Do you use a 64bit Windows? The runtime will, by default, run in 64bit. If your C++ library was compiled targeting 32bit, you will get a BadFormatException upon library loading. The Same goes if your .NET app is running 32bit and your C++ library was compiled targeting x64.
If you can recompile the library, do it. Otherwise you can force the .NET runtime to use a specified architecture at compilation, but it will prevent it from running on the other architecture. It's your choice ;) When coding against .NET or java, we tend to forget what really happen under the hood.

[DllImport("qm-vamp-plugins.dll",EntryPoint="BeatTracker")]
The EntryPoint should be getName(), not BeatTracker which is a class!
But even then you cannot call that, because getName() is member function which cannot be callled without instance.
So I would suggest that define free functions in the DLL, and export them. You can use class internally, in the DLL. You can work with handle of classes.
Example,
DLL code:
typedef BeatTracker* PBeatTracker;
typedef PBeatTracker HBeatTracker;
//exported functions
HBeatTracker CreateBeatTracker()
{
return new BeatTracker();
}
void DeleteBeatTracker(HBeatTracker handle)
{
delete handle;
}
string getName(HBeatTracker handle)
{
return handle->getName();
}
C# Code:
[DllImport("qm-vamp-plugins.dll",EntryPoint="CreateBeatTracker")]
public static extern IntPtr CreateBeatTracker();
[DllImport("qm-vamp-plugins.dll",EntryPoint="DeleteBeatTracker")]
public static extern void DeleteBeatTracker(IntPtr);
[DllImport("qm-vamp-plugins.dll",EntryPoint="getName")]
public static extern string getName(IntPtr);
public QMTempo()
{
IntPtr handle = CreateBeatTracker();
Console.WriteLine(getName(handle));
DeleteBeatTracker(handle);
}

Compile error when calling managed C++ from C#

I am new to .net .
I have a managed C++ library. It looks like this.
// header file
namespace cppnetdll
{
public __gc class Class1
{
public:
static int foo_int(void);
};
}
// source file
namespace cppnetdll
{
int Class1::foo_int(void)
{
return 123;
}
}
I can call this from a managed c++ program. When I try to call it from
a C# program, I get the compiler error: "The type or namespace name
'Class1' could not be found (are you missing a using directive or an
assembly reference?)" The error refers to the DllImport line below.
Here is the C# code
[code:1:a72c1df571]
namespace csuser
{
public class xxx
{
[DllImport("cppnetdll.dll")] extern
int Class1.foo_int();
private void yyy() { int i =
foo_int(); }
}
}[/code:1:a72c1df571]
I have tried various approaches but no success. What is the magic
syntax ?
It's funny that I can call unmanaged C++ functions from C# fairly
easily by declaring the functions as "C" and exporting from the DLL.
I expected calling managed code to be easier. Maybe it's so easy
that no one thought of documenting it !

You do not use a [DllImport] directive to call code that's written in managed C++. That is only intended for native DLLs that export their functions. Neither of which applies to yours, it isn't native and you don't export the function.
You built a managed assembly, you can treat it just like one you'd have written in C#. Project + Add Reference, Browse tab, navigate to the DLL. Or better yet, put both projects in one solution, use the Projects tab to select the reference.

Instead of using the [DllImport ...]
Try just adding a reference, here is a how to from MSDN:
http://msdn.microsoft.com/en-us/library/7314433t%28v=VS.90%29.aspx