I am trying to use MimeTex.dll in Mixed Mode of C++/CLI project. I include the dll by:
#pragma comment(lib,"MimeTex.dll")
and I tried to call this method:
CreateGifFromEq("expression","path");
but the compiler inform that it doesn't know CreateGifFromEq() method.
I didn't find resources in the web in how to use MimeTex.dll in C++. I just find how to use it with C# in this link by Pinvok like:
[System.Security.SuppressUnmanagedCodeSecurity()]
internal class NativeMethods
{
private NativeMethods()
{ //all methods in this class would be static
}
[System.Runtime.InteropServices.DllImport("MimeTex.dll")]
internal static extern int CreateGifFromEq(string expr, string fileName);
[System.Runtime.InteropServices.DllImport("kernel32.dll")]
internal extern static IntPtr GetModuleHandle(string lpModuleName);
[System.Runtime.InteropServices.DllImport("kernel32.dll")]
[return: System.Runtime.InteropServices.MarshalAs(System.Runtime.InteropServices.UnmanagedType.Bool)]
internal extern static bool FreeLibrary(IntPtr hLibModule);
}
and then call it like:
NativeMethods.CreateGifFromEq(equation, tempGifFilePath);
How I can call it without Pinvok in mixed mode of C++/CLI?
Surely you meant to write:
#pragma comment(lib,"MimeTex.lib")
In other words, you pass the .lib file to the linker rather than the .dll. When you compiled the DLL, a .lib file will have been generated.
But that's not your immediate problem. The compiler has no declaration for CreateGifFromEq. That's because you have not included the library's header file in your C++ code. Doing that should resolve the issue.
If all you need is that one function then it should be trivial to declare it in your C++ code.
__declspec(dllimport) extern int CreateGifFromEq(char *expr, char *fileName);
You probably will need to wrap that in an extern "C" block too.
Actually, having looked at the library, the header file that is supplied with the source does not declare that function, even though it's present in the library.
In C++/CLI you can use P/Invoke as in C#.
If you don't want to use P/Invoke, the other way is to load the DLL with LoadLibrary and get pointers to the functions with GetProcAddress.
Here's the equivalent of the C# code in C++/CLI:
using namespace System;
using namespace System::Runtime::InteropServices;
private ref class NativeMethods abstract sealed
{
internal:
[DllImport("MimeTex.dll")]
static int CreateGifFromEq(String^ expr, String^ fileName);
[DllImport("kernel32.dll")]
static IntPtr GetModuleHandle(String^ lpModuleName);
[DllImport("kernel32.dll")]
[returnvalue: MarshalAs(UnmanagedType::Bool)]
static bool FreeLibrary(IntPtr hLibModule);
};
As you can see it's almost identical to the C# code except for some minor syntax changes.
Here's how you would use LoadLibrary and GetProcAddress (which has the advantage of not requiring marshaling, which is unnecessary in C++ anyway):
HMODULE hModule = LoadLibrary(L"MimeTex.dll");
int (*fpCreateGifFromEq)(WCHAR*, WCHAR*) = GetProcAddress(hModule, "CreateGifFromEq");
(*fpCreateGifFromEq)(L"expression", L"filename");
You don't need to do that for GetModuleHandle and FreeLibrary, because they're from kernel32.dll so you can just include Windows.h and call them normally.
There's a cleaner way of doing things:
Create a C++/CLI project. It will be your interface between C# and C++ (this is what C++/CLI is aimed at).
Make your C# project have a reference to this new assembly.
Inside your new C++/CLI project, configure project options so as you point to the directory with mimetex .h files for the compiler to compile your project, and the directory with .lib/.dll for the linker.
Inside your C++/CLI part, you just write C++ inside the functions. They are exposed to your C# assembly, but in the inside it's just calls to C++ functions as usual.
(You should check a C++CLI tutorial to know what to do with strings to convert them to native char or std::string. I remember I had to look at that.)*
In your C# part, you just call the C++CLI project assembly exposed functions like normal C# functions, without noticing it's native code called behind.
Related
I'm trying to use functions from a DLL that can't be added as Reference through Visual Studio (a message saying "reference cannot be added" appears). However, I've gotten instructions from the creator of the DLL and they suggested I use them like this in VB.Net:
Private Declare Function Prn_Init Lib "VAx_VPOS396_APPAPI.dll" () As Integer
That works, but now I want to write a program in C#. How do I "translate" that declaration to C#?
Additional: In C++ the declaration comes in a *.h file with these lines:
#ifndef _VPOS396DLL_API_H
#define _VPOS396DLL_API_H
VPOS396_DLL_API int Prn_Init(void);
You should create the method(s) you want to use in C#, make them extern and add a [DllImport] attribute. For example:
[DllImport("kernel32.dll")]
static extern bool Beep(uint dwFreq, uint dwDuration);
See https://msdn.microsoft.com/en-us/library/aa984739%28v=vs.71%29.aspx
[System.Runtime.InteropServices.DllImport("VAx_VPOS396_APPAPI.dll")]
public static extern unsafe Int32 Prn_Init(void);
("unsafe" is optional)
i have a project in c# that use a unmanaged dll from another project, i have try to import that dll file, but i cannot use that dll file because Visual Studio cannot find its .pdb file, me neither.
i have tried to dll import
[DllImport("unmanaged.dll", EntryPoint= "Analyse", CallingConvention = CallingConvention.Cdecl)]
private static extern unsafe long* Analyse(byte[] bImgData, uint nLength, ushort nWidth, ushort nHeigth, uint nMaxCodeCount, short nAnalyseLevel);
but the method just doesnt return any value.
and in Output List there are:
'CCan.exe' (Win32): Loaded 'C:\Users\Masbro\Documents\Visual Studio 2013\Projects\CCan\CCan\bin\x86\Debug\unmanaged.dll'. Cannot find or open the PDB file.
can i use unmanaged DLL without its pdb file?or can i generate its .pdb file?
You don't need the PDB. However, you do need to know the entry point and function signature of the API you're calling in the DLL; Visual Studio won't figure those out for you. However, if your DLL exports its function names, you can find them using various tools. Some examples here, on MSDN: http://msdn.microsoft.com/en-us/library/vstudio/31d242h4(v=vs.100).aspx
For example, let's say your library, unmanaged.dll, has the following API:
void* DoStuff (DWORD number, LPWSTR str, PDWORD outval);
To call that from C# code, you would need to define the following extern function in in one of your classes:
using System.Runtime.InteropServices
[DllImport("unmanaged.dll", CharSet=Unicode)]
public static extern IntPtr DoStuff (UInt32 number, String str, out UInt32 outval);
The visibility modifier (public) isn't important, except that you need to be able to see the function from wherever you call it. The DllImport attribute is defined in System.Runtime.InteropServices, hence the using statement.
DllImport requires the first value, the string giving the DLL name, but it also has a ton of other parameters which are sometimes helpful or even required (such as CharSet). In particular, if your unmanaged library doesn't export names (or you want to use a different name in C# than the exported unmanaged name) then you need to specify the EntryPoint field of the DllImport attribute. An example of accessing a function without an exported name if you know the function's ordinal:
[DllImport("unmanaged.dll", CharSet=Unicode, EntryPoint="#1")]
public static extern IntPtr DoStuff (UInt32 number, String str, out UInt32 outval);
Take a look at the MSDN documentation for more info.
I'm running VS2012 on Win7 with .NET 4.0.
I've tried the following:
Create C++ DLL project
Checked\Unchecked the export symbols box
I've made sure my platform targets are the same. In my case, win32
I've added the necessary extern "C" and __declspec(dllexport) where needed.
I've successfully compiled my DLL and have tried to reference it in a C# project.
Unfortunately, I get an error telling my it can't be added and that I need to make sure it's a valid assembly or COM object.
I've given up trying to get my code to export, so I'd be happy with just the example "42" getting through!
I've tried looking at it with dumpbin and it is correctly exporting symbols:
1 0 00011023 ??0CEvolutionSimulator##QAE#XZ
2 1 00011127 ??4CEvolutionSimulator##QAEAAV0#ABV0##Z
3 2 00011005 ?GetNumber#CEvolutionSimulator##QAEHXZ
4 3 0001104B ?fnEvolutionSimulator##YAHXZ
5 4 00017128 ?nEvolutionSimulator##3HA
My brain is fresh out of ideas. Can someone please enlighten me? I seem to get this error no matter what I try.
You need to pinvoke the functions residing in your C++ DLL (exported using extern "C") from your .NET code using the DllImportAttribute. You can't reference your C++ DLL like a .NET assembly, and you can't use classes from the DLL, only DllImported C-like functions.
Example from msdn:
using System;
using System.Runtime.InteropServices;
class Example
{
// Use DllImport to import the Win32 MessageBox function.
[DllImport("user32.dll", CharSet = CharSet.Unicode)]
public static extern int MessageBox(IntPtr hWnd, String text, String caption, uint type);
static void Main()
{
// Call the MessageBox function using platform invoke.
MessageBox(new IntPtr(0), "Hello World!", "Hello Dialog", 0);
}
}
I have in C++:
void __declspec(dllexport) foo(HWND wnd)
And in C#
[DllImport("MyDll.dll", CharSet = CharSet.Ansi)]
public static extern void foo(IntPtr wnd);
When I'm trying to call it I have this error - Additional information: Unable to find an entry point named 'foo' in DLL. I tried to inspect the dll and I have the function with the fallowing definition:
Undecorated C++ Function:
void cdecl foo(struct HWND *)
I searched on several forums and is seems that this is the right way to do this... Do you know why I have this run time error?
You need to disable C++ name mangling. Declare your native function like this:
extern "C" __declspec(dllexport) void foo(HWND wnd)
You can use the dumpbin.exe utility to see DLL exports as well.
Long time reader, first time poster. One day I hope to be answering questions on here...
So it's kind of similar to: "Unable to find an entry point named [function] in dll" (c++ to c# type conversion)
But I can't seem to apply the same solution...
Basically, I wrote a new Method:
Defined in the header file of the C++ project as :
extern "C" {
__declspec(dllexport) bool IsDataValid();
}
Defined in the source file of the C++ project as: (signiature only)
extern bool __cdecl IsDataValid() {
//function stuf......... returns a bool
}
Imported into a forms C# application within the C# Project as:
[DllImport("CarChipSDK_C_Sharp.dll", EntryPoint = "IsDataValid")]
[return: MarshalAs(UnmanagedType.Bool)]
public static extern bool IsDataValid();
It is called from the same place within C# forms .cs file as:
bool isDataValid = IsDataValid();
It is returning an exception with the message:
"Unable to find an entry point
'IsDataValid()' named in DLL
'CarChipSDK_C_Sharp.dll'.
I have used dumpbin.exe and dependency walker on the .dll generated from the c++ code and it shows that it has the IsDataValid() entry point.
All help is much appreciated...
Problem Solved! Stupid me, this was the code from a previous co-op at my current company, turns out he was reading the .dll from the bin/release folder where as I was building to the bin/debug folder. Should have known. My sincere apologies.
You are encountering C++ name mangling. Declare the C++ functions as extern "C". So, in your C++ module...
extern "C" __declspec(dllexport) bool IsDataValid();
You really don't need the entry point specification attribute either. Your C# declaration will be:
[DllImport("CarChipSDK_C_Sharp.dll")]
[return: MarshalAs(UnmanagedType.Bool)]
public static extern bool IsDataValid();
For future reference, dumpbin.exe is a very useful program for analyzing problems like this. If you run it on your DLL you will see what those functions are actually named by the time they are compiled.