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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?
Related
I am creating a Windows 10 application that works with files. For the GUI I am using UWP (C#) and for the file processing I want to use the C language (Visual Studio 2019).
I have tried these solutions (none of them worked):
C program created with Windows Desktop Wizard (DLL), then DllImport
Tried to add it to the UWP by using DllImport (which in a C# Console App program worked).
The code in the C file:
#include<stdio.h>
_declspec(dllexport) int getNumberOfFiles()
{
...
}
The code in the C# UWP app:
[DllImport(#"...\WorkFilesDll\Debug\WorkFilesDll.dll", EntryPoint = "getNumberOfFiles", CallingConvention = CallingConvention.Cdecl)]
internal static extern int getNumberOfFiles();
The following exception is thrown:
System.DllNotFoundException HResult=0x80131524 Message=Unable
to load DLL '...\WorkFilesDll\Debug\WorkFilesDll.dll' or one of its
dependencies: Access is denied. (Exception from HRESULT: 0x80070005
(E_ACCESSDENIED))
C program created with Windows Desktop Wizard (DLL), then add as reference
Tried to add the same dll as reference (References->Add Reference->Browse->Add->OK).
After pressing the OK button, the following message indicates the failure:
A reference to "...\WorkFilesDll\Debug\WorkFilesDll.dll" could not be
added. Please make sure that the file is accessible, and that is a
valid assembly or COM component.
I created other types of projects for the C code (C++, UWP): Dll (Universal Windows), Windows Runtime Component (Universal Windows). The results were the same.
I created other types of projects (C#, UWP): Class Library (Universal Windows), Windows Runtime Component (Universal Windows), in order to add theses projects to the UWP and to add to these projects the dll mentioned above (the C code to be added indirectly to the UWP). The results were the same.
I have found many questions and articles like this, but I didn't see a clear answer or the answers didn't work for me. Some of them are:
https://learn.microsoft.com/en-us/cpp/cppcx/dlls-c-cx?view=msvc-160
https://www.c-sharpcorner.com/forums/how-to-use-cpp-dlls-in-c-sharp-uwp-projects
How to call a function from DLL in UWP?
Can you use C++ DLLs in C# code in a UWP?
https://learn.microsoft.com/en-us/cpp/porting/how-to-use-existing-cpp-code-in-a-universal-windows-platform-app?view=msvc-160
I have also read about static libraries. I have failed in implementing them.
How can I put the C code in UWP (C#)?
Are static libraries the answer to my application?
Which are better for this application: the DLLs or the static libraries? Why?
Thank you!
Please check the following steps:
Create a C# UWP project in a new solution.
Add a C++ DLL(Universal Windows) project(named MyDll1) in the same solution.
Add your C code in the C++ DLL project. For example:
//MyDll1.h
#pragma once
extern "C" _declspec(dllexport) int Sum(int a, int b);
//MyDll1.cpp
#include "pch.h"
#include "MyDll1.h"
int Sum(int a, int b)
{
return a + b;
}
Add a Windows Runtime Component(C++/WinRT) project in the same project.
Right-click on the name of the Windows Runtime Component(C++/WinRT) project, and select option Add > Reference, check your DLL project in Projects tab. Click OK.
There is an auto-generated class Class, you could use the class or add other class(Add > New Item > Code > Midl File(.idl)) as needed. The new class must be generated from a midl file. You could get more information about authoring api referring to the document.
Take Class class as an example. Include the header file of dll in Windows Runtime Component(C++/WinRT) project.
//Class.h
#include "..\MyDll1\MyDll1.h"
There is a sample method named MyProperty shown in Class class. The MyProperty method is added to the Class.idl file and the complier will generate the corresponding methods in Class.h and Class.cpp after you build the project. And you need to go to the locations \RuntimeComponent\ RuntimeComponent \Generated Files\sources\Class.h and Class.cpp in File Explorer and open the .h and .cpp file to copy the generated methods into your code in Visual Studio. You could use MyProperty method to pass values to C# project or add other methods in classes. Refer to the document for more information about how to add new method in idl file.
You could call the Sum(int a, int b) of MyDll1 project in MyProperty method.
int32_t Class::MyProperty()
{
int t = Sum(1, 2);
return t;
}
Right-click on the name of the C# UWP project, and select option Add > Reference, check your Windows Runtime Component(C++/WinRT) project in Projects. Click OK.
Add include statement in C# UWP project.
using RuntimeComponent; // RuntimeComponent is the name of Windows Runtime Component(C++/WinRT) project.
You could call the MyProperty method in C# UWP project.
RuntimeComponent.Class myClass = new Class();
var value = myClass.MyProperty;
I have code written in ANSI C that I would like to use in C#. I have compiled the C code into a DLL and created C# wrapper classes to interop with the C code. The point of the wrapper is to simplify a users interaction with the underlying C code.
[DllImport(DLL, CharSet = CharSet.Ansi, CallingConvention = CallingConvention.Cdecl)]
private static extern void PrintHelloWorld();
public void PrintHelloWorldC()
{
PrintHelloWorld();
}
Above is a simplified example of what I have done so far. Now, I am trying to create a DLL from the C# wrapper classes I wrote. From here I could give both the DLLs created and someone would be able to interact with the C# based DLL to interact with the underlying C based DLL. Below is what I have done and what problem I am having.
I compile the C code into a DLL in Visual Studio 2019 with my Configuration=Release and Platform=Win32.
I compile my C# classes into a DLL in Visual Studio 2019 with my
Configuration=Release, Platform=Win32, and Platform Target as x86.
I create a new project and link my C# DLL and set Platform Target as x86.
I put my C DLL into the Debug folder of the project so that it is available to the C# DLL through the marshal directive.
I try to make a call into the C# DLL and below are the chain of events occurring.
Program calls C# DLL method PrintHelloWorldC() and is successful
Within PrintHelloWorldC() it tries to make a call to PrintHelloWorld();.
Following Error Occurs:
System.BadImageFormatException
HResult=0x8007000B
Message=An attempt was made to load a program with an incorrect format. (Exception from HRESULT: 0x8007000B)
My research yielded that it was most likely a mismatch in Platform Target between the DLLs and Test Project, however, I have double checked all the configurations and they should all be compiled for x86.
Below is what additional testing I have done.
Created a C# Project, and wrote simple code to make a call directly into the C based DLL. This works fine.
It seems that as soon as I try to use the two DLLs on top of each other in another project I start facing issues.
Any help or guidance is appreciated. Thanks in advance!
Update
I have now run through the tutorial 3 times with the same results (Visual Studio/Windows is unable to recognise the DLL as a valid file). This must be an issue with my environment, as mike below ran through the tutorial and it worked fine.
I did notice this in the C++ project's solution explorer on my last run:
Does anyone know if this is okay? There seems to be a lot of Red stop-signs which to me would suggest something bad...
Following this tutorial, I have ended up with the following:
C#
using System.Runtime.InteropServices;
namespace TestImport
{
class Program
{
[DllImport("TestLib.dll")]
public static extern void DisplayHelloFromDLL();
static void Main(string[] args)
{
DisplayHelloFromDLL();
}
}
}
C++
In .cpp file Source Files
#include <stdio.h>
extern "C"
{
__declspec(dllexport) void DisplayHelloFromDLL()
{
printf("Hello from DLL !\n");
}
}
When debugging in Visual Studio:
An unhandled exception of type 'System.DllNotFoundException' occurred in TestImport.exe
Additional information: An attempt was made to load a program with an incorrect format. (Exception from HRESULT: 0x8007000B)
When running the built EXE (from he same folder as the Dll):
An attempt was made to load a program with an incorrect format.
Have I done anything wrong in the above code?
I did do all of this in VS 2015, where the tutorial calls for VS 2010, howeve rI couldn't find a more up-to-date tutorial.
When I try to add the project as a reference by Project -> Add Reference ... I am seeing this error:
A reference to 'Path\To\MyLib.dll' could not be added. Please make sure
that the file is accessible, and that it is a valid assembly or COM
component.
Which makes me think that the issue is either with the source code or the DLLs configuration.
I have also tried building both files and putting them in the same folder before running the Executable, but without any improved results (same error as when running the EXE above).
Solution Explorer Screenshot:
Make sure the name of your C++ project and DllImport parameter are the same. Also, if the dll file is not located in the same directory as your C# project, make sure to add the dll into your Debug/Release folder.
Also! Make sure that you are running in the same 32/64 bit mode when compiling.. if you compiled the dll using 32 bit and try to use it in a 64 bit C# program, it won't work.
OK, now build this application, and then copy the previously built DLL into the Debug/Release directory of the current application. The DLL should be in the same directory as your main application.
Did you do the bolded text? Your C# app won't know where to look for the DLL and it looks in the build folder, by default.
An unhandled exception of type 'System.DllNotFoundException'
It happened to me, because of the imported c++ dll, its own dependency dlls were missing.
After copying them into Debug/Release folder everything worked.
I want to reference/include and C++ dll file in to my C# class libary, with a normal C# windows form I just put the dll in the working directory, this does not seem to work for class libraries, how do I get it to find the .dll?
[System.Runtime.InteropServices.DllImportAttribute("ve.dll", EntryPoint=<MethodName>, CallingConvention = System.Runtime.InteropServices.CallingConvention.Cdecl)]
That is the call to the methods and the DLL I am including is in the build folder.
You may need a post-build step to ensure that the DLL is copied to your build output folder when you recompile the application. Once that's done, the DLLImport attribute should be able to find the DLL using the short name of the file, without any path information (since it will be local to the executing assembly).
The c++ dll needs to be either local to the hosting exe (if the hosting exe references the c# dll it will copy that local to itself on build) or in a location in the system PATH environment variable.
You can add the c++ dll to the c# project (Add ->Existing Item -> All Files) and set Copy to Output Directory to Copy if newer or Copy Always and set Build Action to None (IIRC the default option)
If it isn't a managed DLL then you need to use the DllImport attribute. Assuming the DLL has exported functions. You can check the exported function names using dumpbin /exports
private const string DLLPATH = "MyDLL.dll";
[DllImport(DLLPATH, EntryPoint = "GetDLLStatus")]
public static extern int GetDLLStatus();
[DllImport(DLLPATH, EntryPoint = "SomeOtherFunction")]
public static extern float SomeOtherFunction();
DllImport will first look for the DLL in the application directory then look in your path
In my project I have an unmanaged native C++ dll and a C# application. I am trying to import a function from the unmanaged dll using DllImport but I keep getting a DllNotFoundException.
Here is my code that calls the DLL.
using System.Runtime.InteropServices;
namespace TestApp
{
public delegate void UpdateDelegate(string s);
class Program
{
[DllImport("CGPUnmanagedLibrary.dll")]
internal static extern int parse_raw_gsod_file(
[MarshalAs(UnmanagedType.LPStr)]
string filePath,
int minTemp,
UpdateDelegate callBack);
static void Main(string[] args)
{
UpdateDelegate myCallBack = new UpdateDelegate(Program.Report);
string path = #"C:\Creative Solutions\Projects\Clyde's Garden Planner\Frost Data Database\GSOD Data\GSOD_RAW_DATA\1992\gsod_1992.txt";
int result = parse_raw_gsod_file(path, 32, myCallBack);
Console.Write("Parse completed with exit code: " + result.ToString());
Console.ReadLine();
} // end main function
public static void Report(string msg)
{
Console.Write("Message is ");
Console.WriteLine(msg);
}
} // End class
} // end namespace
I tried copying the DLL to the app output directory but it still can't find it. I also tried adding the DLL project as a reference but I get a popup window saying it can't be added. How do you properly link an unmanged DLL to a managed application?
Update - Here is the full error:
Unable to load DLL 'CGPUnmanagedLibrary': The specified module could not be found. (Exception from HRESULT: 0x8007007E)
Update 2 - I know for sure that the DLL is in the same directory as the .exe trying to load it. This makes me think there is a dependency in the DLL that isn't getting loaded. I'm only using basic C++ libraries in the DLL (string, math, iostream, etc). Any ideas what could not be loading and why?
Update 3 - Tested with Dependency Walker
Loading my unmanaged C++ DLL in dependency walker showed no errors. I also tried to open my executable in dependency walker and it showed errors loading two DLLs: GPSVC.DLL and IESHIMS.DLL - doesn't make any sense because I am only using standard c++ libraries in my code. I think it may have something to do with the fact that I have a managed C++/CLI DLL trying to load the unmanaged DLL as well (I was trying to implement some C++/CLI wrappers). Anyway, I have since started a new VS solution and moved on. See my answer.
In all likelihood the problem isn't the DLL you're trying to load but one of its (chained) dependencies. Run depends.exe or a similar utility on the DLL to see if all the dependencies can be found. The misleading message "The specified module could not be found" has become a classic annoyance (if not FAQ material!): it leads you to think that your DLL is not being found when almost all of the time it's one of its dependencies that's not being found.
To test, the *.dll needs to be in the same directory as the .exe that is trying to load it. Don't trust Visual Studio to do it for you at this point. Physically copy the file to C:******\Debug\x86\bin\ or whichever configuration you are running under. If in doubt, copy it to all of your bin folders. After you figure out the path, then you start finding ways to automate the project build to copy the file correctly. If that doesn't do it, put it in system32--it will certainly find it there. However, if after doing these things, you still can't find it. There is probably a dependency to your unmanaged dll that is also missing.
First I want to thank everyone for their help. Unfortunately I never did solve this issue (see edits in my main question). The answer turned out to be starting a totally new Visual Studio solution and creating two new projects: C# app and C++ dll. I did away with the need for wrappers as I am now just marshaling two main functions.
Thanks again.
The anwer of user arayq2 made much sense and I was quickly able to solve my problem also.
The dll that couldn't be loaded (DllNotFoundException) in my case is depending upon another dll. This dll (that is not part of my project) was actually compiled with newer versions of certain .h and .lib files. Older versions of these .h and .lib files (with the same filename) were part of the project that compiled the dll that couldn't be loaded.
After I updated my dll project with the newer versions of these .h and .lib files and recompiling my dll project, my problem was solved.
Thank you arayq2!