I want to use C# to call c++ dll file to get data.
In C++,
extern "C" int _DLLExport Process_Read( char **msg );
In C#,
[DllImport( "ProcessExport" )]
public static extern int Process_Read( ref string msg );
=================
string msg;
int msg_len = 0;
msg_len = Process_Read( ref msg );
=================
How could I show the msg data?
Thank you.
DllImport can only be used to import C functions, not C++ class methods (even if they are static).
If its a c++ com object if you register it with regsvr32 you can add a reference to the dll in visual studio com references tab and usually visual studio creates an dll (I think its called a runtime callable wrapper) which you can see is created with the nameoflibrary.interop.dll. So MyExecRefsDll.dll if were a com object would become MyExexRefs.Interop.dll. But when you add the reference visual studio usually does this for you automatically in managed code. If you create a c++ dll as a com object by using atl template in c++ it is easier to access from dotnet (Iam referencing unmanaged c++ code from a dll which references another dll file (No code copied from the second dll I just reference the tlb, lib, the dll file, and visual studio does everything else.
Take a look at this tutorial it makes the process as clear as a crystal ball:
http://www.codeproject.com/Articles/505791/A-Beginner-Tutorial-for-Writing-Simple-COM-ATL-DLL?q=creating+an+atl+dll+c%2b%2b
Just remember to find the tlb and lib (usually in the folder where the other dll is created after compiling. ) and reference them by right clicking in solution explorer and add->existing item for the second dll referenced from the main dll. The tlb and lib allow you to call functions from the dll (always copy new versions of them into your projects folder everytime you update the code to the second dll).
Related
I have unmanaged dll that I do from my c# dllImport and call to functions from this dll.
What i done now is to copy this dll to my Realese and Debuge folders , and dllImport i call to this dll without any path.
What is the right way?
How can I add this unmanaged dll to my project that is automaticly will be in my realsae and debug folders. ( I can't wimple done add refernce with this dll because it unmanaged dll ).
And witch path should I write on the path on dllImport.
What is the right way?
" copy this dll to my Realese and Debuge folders" works. you may try post build (in native c++ project) or pre build (in C# project)
This question already has answers here:
Is it possible to embed C code in a C# project?
(4 answers)
Closed 5 years ago.
I am confused on how to reference my c code from my c# code. I have read around and realized that DLL's are useful, but I do not understand how to connect my dll. From my understanding I make the dll from my c code? Please help
C# (visual studio code)
public partial class Form1: Form{
[DllImport("simple.dll", CallingConvention = CallingConvention.Cdec1)]
public static extern void pinfo(string str);
private void button1_Click(object sender, EventArgs e){
pinfo("yay");
}
}
C code - simple.c
#include <stdlib.h>
#include <stdio.h>
#include <time.h>
__declspec( dllexport ) void pinfo(char* str){
printf("You are in the method %s\n, str);
}
int main(void){
}
my question is how do I connect the c code to the c# code so that the line "You are in the method yay" prints out? I do not understand how to link a dll file to visual studio or how to create the dll file. thanks
There are 3 main steps for getting P/Invoke (DllImport) working in .NET:
Export the function from the C/C++ project.
In Visual C++, use the __declspec( dllexport ) and extern "C" modifiers to, respectively, tell the compiler to export the function in the DLL so it is visible by name, and to not mangle the name either - otherwise the compiler will remove the function entirely if it has no callers inside the project ("dead-code removal"). Functions can also be exported by an ordinal number instead, which presumably is not what you're interested in.
Ensure you're building for the same ISA.
When you use P/Invoke in .NET, the DLL you reference will be loaded into the hosting .NET process, so the DLL must be built to the same CPU instruction-set as the current .NET process. .NET projects run in AnyCPU mode by default, but in recent versions of Visual Studio they "prefer" 32-bit (x86) mode instead of 64-bit (x64 / AMD64). To prevent any confusion, decide if you want 32-bit or 64-bit mode and force your .NET project to build only for that ISA and then set your C/C++ project to build for that ISA too.
Ensure the target DLL file is located in the PATH of the .NET executable - typically this means simply placing it in the same bin output directory as the built .NET executable.
Note that as this DLL file is not a .NET assembly there is no concept of a "project reference" or "assembly reference", so you need to configure your project specifically so that Visual Studio (MSBuild) will copy the DLL file to your bin folder - you can do this by adding the DLL file to your .NET project root in Solution Explorer, then selecting the file and open the Properties window and choose "Build action: Content." and "Copy to output directory: Always".
Regarding "linking" - DLLs are not linked at compile-time - the clue is in the name: "dynamic-linking": the linking is performed at runtime by the operating system, not by the compiler.
For more information on P/Invoke, I recommend reading this QA: Why are Cdecl calls often mismatched in the "standard" P/Invoke Convention?
I am using SWIG to generate a DLL that will expose C++ functionality to a C# project. At the moment I:
Define a SWIG interface file
%module example
%{
/* Includes the header in the wrapper code */
#include "../pointmatcher/PointMatcher.h"
%}
...
%include "../pointmatcher/PointMatcher.h"
Use SWIG to generate a .cxx wrapper
swig.exe -c++ -csharp -outdir csharp example.i
Compile the .cxx wrapper with MSBUILD via CMake
# create wrapper DLL
add_library(example SHARED ${WRAP_CSHARP_FILE})
target_link_libraries(example pointmatcher)
install(TARGETS example
ARCHIVE DESTINATION ${INSTALL_LIB_DIR}
LIBRARY DESTINATION ${INSTALL_LIB_DIR}
RUNTIME DESTINATION ${INSTALL_BIN_DIR})
I then have a DLL file (example.dll) which I can inspect via Dependency Walker, and confirm that methods are being exposed as follows:
However, when I try to add this MSVC DLL as a reference to a C# project I get the error "It is not a valid assembly or COM component".
Based on answers at How can I add a VC++ DLL as a reference in my C# Visual Studio project? I have confirmed that SWIG itself generates P/Invoke calls, and that tlbimp doesn't recognise the DLL either.
You don't add the C++ dll to your project in the same way you would a C# dll. Instead it is called through the PInvoke system.
SWIG will generate some C# code for you, the easiest way to access the dll is to include those files in your porject, which expose the dll functionality through some C# functions which you can call.
You can also use the dll through PInvoke yourself. You need to create a C# function that will act as a wrapper:
C++ Header:
#ifndef TESTLIB_H
#define TESTLIB_H
extern "C" {
int myfunc(int a);
}
#endif
C++ Code:
int myfunc(int a)
{
return a+1;
}
C# Code:
using System;
using System.Runtime.InteropServices;
class Libtest
{
[DllImport ("function")]
private static extern int myfunc(int a);
public static void Main()
{
int val = 1;
Console.WriteLine(myfunc(val));
}
}
Output:
2
Location of the DLL
The compiled C++ dll needs to either be copied into the C# project bin directory, or if the path is known it can be added to the DllImport call:
[DllImport("path/to/dll/function.dll")]
To achieve this with swig use the -dllimport flag:
swig -cpp -csharp ... -dllimport "/path/to/dll/function.dll" ...
If you want to set the path dynamically (to allow for loading 32-bit or 64-bit versions dynamically selected at runtime) you can use the kernel32 function SetDllDirectory which is also loaded using DllImport.
I am new to Visual Studio 2010,
I have the DLL written with C# , and it is working with VB.NET , Now I want to use it with VC++, Can you help me ?
If you are planning on using .NET extensions in your VC++ project, you just need to add a reference to your C# DLL in your VC++ project.
If you're planning to use pure C++, you'll need to change your C# DLL to be COM-Visible, and generate a typelib that you'll import in your C++ project.
You can access functions from native DLL (written in C++) from .NET using PInvoke. To use managed DLL from native code (eg. call C# method from C++ code) you have to wrap managed code in COM component and use that COM object from C++
Going the other way is easy using P/invoke. Calling managed code from unmanaged is tricker. One good option is COM, but there is an alternative. Robert Giesecke has published an excellent project that allows you to expose managed methods as unmanaged DLL exports.
It's very simple to use. You simply download the Visual Studio template, create a project based on that, add your code, and mark exports with the DllExport attribute.
Or you can create Manager C++ DLL that will reference and implement all or custom objects from C# DLL.
After than you can create dllexport methods in your MCPP DLL.
And then you can access C# DLL thru MCPP DLL using LoadLibrary(...)/GetProcAddress(...) methods.
Example:
using namespace System;
using namespace System::Windows::Forms;
__declspec(dllexport) LPVOID GetPluginInterface()
{
return (IWithExecuteCommandMethod*)&theApp;
}
bool CClass::ExecuteCommand()
{
if(Threading::Thread::CurrentThread->TrySetApartmentState(System::Threading::ApartmentState::STA))
{
Flatbed::SomeDialog ^pDialog=gcnew Flatbed::SomeDialog();
pDialog->ShowDialog();
}
else
{
Threading::Thread ^pDialog=gcnew Threading::Thread(gcnew Threading::ThreadStart(ThreadProc));
pDialog->SetApartmentState(Threading::ApartmentState::STA);
pDialog->Start();
}
return false;
}
I am wrote a visual c++ win32 console app, and i wrote it and tested it in
win32 console project
. then i switch to
win32 project
and imported all the source files and created a dll for it. by mark the class i want to export as
#define DllExport __declspec( dllexport )
class DllExport theClass {
}
it works and the dll is generated. then i created a another c# project and want to add the dll to the project. by reference->add reference-> browser. then i select that dll.
then it is gives me an error
a reference to the '''''''.dll could
not be added. please make sure that
the file is accessible, and that is a
valid assembly or com component.
anyone knows where i did wrong to generate/import the dll?
thanks
The Add Reference dialog can only work for DLLs that contain metadata (managed code) or a type library (a COM server). Your DLL doesn't fit that bill, you can only use the [DllImport] attribute in C# code to use the P/Invoke marshaller to call an unmanaged DLL entrypoint.
That can not be a native C++ class, like you are trying to do, there is no reliable mechanism for managed code to allocate unmanaged memory and call the constructor (and destructor) of a native C++ class. Short from the difficulty of finding the constructor and destructor code, there is no way for the P/Invoke marshaller to know the size of the object. The C++ language doesn't generate the metadata necessary to know this required information.
If you want to pursue P/Invoke then write an plain global function, decorated with extern "C", __declspec(dllexport) and (optionally) __stdcall.
If you want to export a C++ class then the only avenue is using the C++/CLI language and write a "ref class" wrapper for the native C++ class.
Or you could write a COM coclass, the universal glue in Windows. Very well supported by .NET, probably not something you want to pursue if you never wrote COM code before. ATL is the best way to get one going.