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
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Is it possible to embed C code in a C# project?
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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'm trying to import a C++ Project Dll into a C# project. I found a lot of people talk about using DllImport. I tried using that and here is what I have-
CPP Code:
int __declspec(dllexport) beginCode(double reportId);
C# Code:
[DllImport("C:\\Users\\<my_user_id>\\Desktop\\ctxmix\\Release\\ctxmix.dll",CallingConvention =CallingConvention.Cdecl ,CharSet = CharSet.Ansi, SetLastError = true, ExactSpelling = true)]
public static extern int beginCode(double reportId);
int result = beginCode(reportId);
But when I run, I'm getting an exception - Exception thrown:
System.DllNotFoundException
Do I have to add any references for the CPP Dll in the project or do anything else apart from the code which I have on the top?
Edit: I'm trying to run my .exe using VS2015 and I get this exception on my local machine. Also, I don't see my CPP Dll in the Project->References section where as I see other references there.
The unmanaged DLL needs to be locateable by your managed process. Typically that means placing the DLL in the same directory as the executable file. But you gave used an absolute path which I presume you transcribed correctly.
You may also encounter this error if the DLL's dependencies cannot be located. That seems the likely explanation here. Most likely the MSVC runtime cannot be located when your DLL is loaded.
Using an absolute path isn't a great idea. That will break down when you distribute to another machine. Use just the DLL file name and place it in the same directory as the executable.
Your DllImport attribute seems fussy. No point specifying CharSet when there is no text. I doubt your function calls SetLastError. And do you really need ExactSpelling?
I have a solution with C#, C++ & C++/CLI projects. To be more specific: it is C++ core (~5 unmanaged dll's), C++/CLI core wrapper and C# assemblies with project-specific buisness logic.
Some time ago I figured out that VS 2008 form designer (WinForms) sometimes can't load core wrapper assembly. After a few hours spent with VS debugger and Procmon I found out that VS can't load assembly because it can't resolve unmanaged libraries that wrapper depends on. VS searches in every system folder and folder from PATH environment variable, but not in folder where wrapper assembly is located.
Moreover, I have 2 forms in one assembly, one is inherited from another: VS form designer loads parent form fine and fails with loading an inherited form.
So, here is my question: does anyone knows the reason of this behavior?
P.S. I used workaround: added folder with project binaries to PATH variable, but I still want to know the reason.
Did you try to put the binaries into the executables folder? Because i'm sure that .NET is only searching for know paths ( As path's stored in %PATH% ) and the local folder of the executable.
I don't know the exact reason for this, but i think this is because the DLL doesn't know the path where it has been loaded from ( managed DLL's do! ) and only looking in the current directory and other known paths.
But there are a workaround for this, you could create a startup executable for Visual-Studio and do one of the following things:
Modify the %PATH% variable with Environment.SetEnvironmentVariable
Use the Kernel32.dll method SetDllDirectory
SetDllDirectory-Snippet:
[DllImport("kernel32.dll", SetLastError = true)]
public static extern Boolean SetDllDirectory(String pathName);
I have a .dll that I generated thorugh a C++ project. I have to use this dll in my ASP.NET project and I have written DllImport functions for the same in my project.
The static class inside App_Code has some DllImport functions
public static class Functions
{
[DllImport("MyFav.dll", EntryPoint = "fnmain",
CallingConvention = CallingConvention.Cdecl, CharSet = CharSet.Ansi)]
public static extern StringBuilder fnmain();
}
Since I could not add the C++ dll directly as a reference in my ASP.NET project (because it is not a .NET assembly), I just copied into the top level directory. ( Name of ASP.NET Project-> Right Click -> Add Existing Item )
Now, when I try to run the project, I get the following error:
Exception:
Unable to load DLL 'MyFav.dll': The specified module could not be found. (Exception from HRESULT: 0x8007007E)
Any suggestions? Where has the .dll to be kept?
The .dll should be in the \bin folder of your asp.net application.
Apparently there are rules for how dlls are resolved. See Dynamic-Link Library Search Order on msdn
You could also try:
[DllImport("C:\path_to_dll\MyFav.dll", EntryPoint = "fnmain",
CallingConvention = CallingConvention.Cdecl, CharSet = CharSet.Ansi)]
public static extern StringBuilder fnmain();
If all this doesn't work, maybe your MyFav.dll has additional unresolved dependencies. You could use Dependency Walker to check for these.
I had a similar error, but using Mono's XSP server. For this server, the solution is to put the dll in the root of your web app (the parent folder of ./bin). That happens to also be the current working directory (when run from Xamarin Studio), which is presumaby related.
if to be used with out path copy paste the dll to bin directory in your project folder
.
I have a C# winapp. I call a native .dll file (created in C++ by myself) from the C# app, and it works fine.
But when I copy my application (.exe and .dll files) to another machine, I get an error that says:
Unable to load DLL "c:\dllname.dll": The specified module could not be found. (Exception from HRESULT: 0x8007007E)
Here is the C# code:
class IsoMessageHelper
{
public const string ISO8583_DLL = "c:\\Hc8583.dll";
[DllImport(ISO8583_DLL, CallingConvention = CallingConvention.Cdecl)]
public static extern bool InitializationRq(...)
}
What should I do?
A common issue when deploying .Net applications that have native dependencies, is that the native dlls may be missing dependencies themselves on the target machines e.g. the correct version of the C runtime.
Use a tool such a Dependency Walker to analyze your native dll and determine if it has a missing dependency on the machine you have copied it too.
Try not to hard code any paths in the DllImport attribute parameter that specifies the name of the file. Then you should make usre the file is right besides the executable.
Something like this:
[DllImport("user32.dll", CharSet = CharSet.Unicode)]
Move the DLL to the root. If that works, then look at your attribute to determine why. You haven't posted any code, so I can't give you any specific reason.