The question is easy, Want to read a string from managed C# code to my unmanaged C++ code in WCHAR* [].
The C function is:
extern "C" __declspec(dllexport) int __cdecl myfunc(int argc, WCHAR* argv[])
and in C# I imported the DLL:
[DllImport("mydll.dll", CharSet = CharSet.Auto, SetLastError = true, CallingConvention = CallingConvention.Cdecl)]
public static extern int myfunc(int argc, [MarshalAs(UnmanagedType.LPTStr)] StringBuilder str);
I run, but when I tried to read the string in my C++ code I get AccessViolationException : Attempted to read or write protected memory. This is often an indication that other memory is corrupt.
What is the correct way to do this and vice versa (i.e. passing a string from C++ unmanaged to C# managed code)?
Help Appreciated.
Thanks
It seems that your C function expects an array of strings, and you're passing a single string instead.
I haven't used P/Invoke myself, but this question might provide some insight.
I am not sure about C# to C++ but i can help you out in your C++ to C# problem.
Export the function from C++ code like this:
DllExport std::string MyFunction( std::string MyParameter) ;
This can be imported in your C# code as:
[DllImport("DLLName.dll", EntryPoint = "MyFunction", CallingConvention = CallingConvention.StdCall, CharSet = CharSet.Ansi)]
[return: MarshalAs(UnmanagedType.LPStr)]
public static extern string MyFunction([System.Runtime.InteropServices.InAttribute()] [System.Runtime.InteropServices.MarshalAsAttribute(System.Runtime.InteropServices.UnmanagedType.LPStr)] string MyParameter);
Now, in your C# code the function "MyFunction" will take in a string and return a string. You can then call MyFunction and the operations can be carried out.
If you are using a WCHAR*, perhaps you should try marshalling as UnmanagedType.LPWStr instead to avoid passing half as much memory as expected?
The documentation on Default Marshaling for Strings should provide you with more details.
Related
I'm not that good in C++
but,..
For example I have this
#define GETSomthing_API __declspec(dllexport)
extern GETSomthing_API int nGetSomthing;
And the method I want to import like this
GETSomthing_API int GetSomthing(const char* szConfigPath, char *A, int B)
How Can I call this from C# ?
Beside,
I think my problem is with the parameter type (const char* ) in C++ side, what is the equal type in C# for it! const char*
Thanks,
How to call C++ code from C#
or
Calling C++ function from C#
Using: [DllImport("xxx.dll")] xxx.dll is compile by C++
Hope this help.
There are a couple of ways for calling into native code from C#. The easiest is probably to use P/Invoke.
Say your function is like :
extern "C" int nGetSomeThing(void);
and it is compiled into a YourDllName.dll file, you can use P/Invoke to directly call into the unmanaged code in the following way from C# code :
public static class interop
{
[DllImport("YourDllName.dll")]
static extern public int nGetSomeThing(void);
}
...
interop.nGetSomething() // call to the native function
Refer : http://msdn.microsoft.com/en-us/library/aa288468%28VS.71%29.aspx.
If you have a lot of functions with complex signatures, you should probably go for an interop layer in C++/CLI.
Refer : http://www.codeproject.com/Articles/19354/Quick-C-CLI-Learn-C-CLI-in-less-than-10-minutes
I just added __cplusplus check and it worked!
#ifdef __cplusplus
extern "C" {
endif
GETSomthing_API char* GetAgentId(const char* szConfigPath, char *szA, int ASize);
ifdef __cplusplus
}
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
pinvokestackimbalance — how can I fix this or turn it off?
I need to access a c++ dll library (I don't have the source code) from c# code.
for example the following functions:
UINT32 myfunc1()
UINT32 myfunc2(IN char * var1)
UINT32 myfunc3(IN char * var1, OUT UINT32 * var2)
For myfunc1 I have no problems when I use the following code:
[DllImport("mydll.dll")]
public static extern int myfunc1();
On the other hand I was unable to use myfunc2 and myfunc3.
For myfunc2 I tried the following: (and many others desperately)
[DllImport("mydll.dll")]
public static extern int myfunc2(string var1);
[DllImport("mydll.dll")]
public static extern int myfunc2([MarshalAs(UnmanagedType.LPStr)] string var1);
[DllImport("mydll.dll")]
public static extern int myfunc2(char[] var1);
But all of them gave the following error:
"Managed Debugging Assistant 'PInvokeStackImbalance' has detected a problem in 'C:\Users\....\myproject\bin\Debug\myproj.vshost.exe'.
Additional Information: A call to PInvoke function 'myproject!myproject.mydll::myfunc2' has unbalanced the stack. This is likely because the managed PInvoke signature does not match the unmanaged target signature. Check that the calling convention and parameters of the PInvoke signature match the target unmanaged signature."
Please, guide on what I should do.
Your C++ functions use the cdecl calling convention, but the default calling convention for DllImport is stdcall. This calling convention mismatch is the most common cause of the stack imbalanced MDA error.
You fix the problem by making the calling conventions match. The easiest way to do that is to change the C# code to specify cdecl like this:
[DllImport("mydll.dll", CallingConvention=CallingConvention.Cdecl)]
public static extern int myfunc2(string var1);
It might just be a character set mismatch try this
[DllImport("mydll.dll", CharSet = CharSet.Ansi)]
public static extern int SendText([MarshalAs(UnmanagedType.LPStr)] string var1);
Nicked from:
DLL import char * pointer from C#
I have a c++ function like,
extern "C" __declspec ( dllexport ) DWORD GetSizeAfterMergeISOTemplates(BYTE* StoredISOTemplate, BYTE* CapturedISOTemplate)
{
}
I would like to return the size of array after merging the two byte arrays in the argument. The c++ part is working and its returning the correct value.
But my problem is I need to get the value in DWORD in c#. The function is,
[DllImport("XFPLibISO")]
extern static UInt32 GetSizeAfterMergeISOTemplates(Byte[] StoredISOTemplate, Byte[] CapturedISOTemplate);
But its returning the wrong value. Its 3477800 something. But actual value is around 964.
Can anybody suggest how can I do this?
C++ function you provided means CallingConvention.Cdecl. You must specify it, when applying DllImportAttribute:
[DllImport("XFPLibISO", CallingConvention = CallingConvention.Cdecl)]
I have a C++ DLL that I am trying to interface with using C#. I do not have access to the DLL source code so it cannot be changed. One of the methods I need to call contains a pointer to an unsigned long:
int __stdcall Foo(FooHandle messageHandle, unsigned long* tag, char* part, char* value)
I have created a test DLL project with the same method signature so I can try to figure this out but I have not successfully been able to have the DLL change the value of the unsigned long that the pointer is referencing and get that value back on the C# side. The C# side declaration is:
[DllImport("Foo.dll", EntryPoint = "Foo", CallingConvention = CallingConvention.StdCall)]
public static extern int Foo(int messageHandle, IntPtr tag, StringBuilder part, StringBuilder value);
When I make the call from C# and then try to convert the IntPtr to Int32 or Int64 I get a zero. I have searched on here and the net in general as well as MSDN and can't seem to find an explaination of how to do this. I figured the char* would be the hard part but the StringBuilder just works.
How can you use a C++ DLL that changes the value of an unsigned long that is passed by pointer?
Any help would be appreciated. Thanks.
Just use a uint passed by ref:
public static extern int Foo(int messageHandle, ref uint tag, StringBuilder part, StringBuilder value);
After switching to VS2010, the managed debug assistant is displaying an error about an unbalanced stack from a call to an unmanaged C++ function from a C# application.
The usuals suspects don't seem to be causing the issue. Is there something else I should check? The VS2008 built C++ dll and C# application never had a problem, no weird or mysterious bugs - yeah, I know that doesn't mean much.
Here are the things that were checked:
The dll name is correct.
The entry point name is correct and has been verified with depends.exe - the code has to use the mangled name and it does.
The calling convention is correct.
The sizes and types all seem to be correct.
The character set is correct.
There doesn't seem to be any issues after ignoring the error and there isn't an issue when running outside the debugger.
C#:
[DllImport("Correct.dll", EntryPoint = "SuperSpecialOpenFileFunc", CallingConvention = CallingConvention.StdCall, CharSet = CharSet.Ansi, ExactSpelling = true)]
public static extern short SuperSpecialOpenFileFunc(ref SuperSpecialStruct stuff);
[StructLayout(LayoutKind.Sequential, Pack = 1, CharSet = CharSet.Ansi)]
public struct SuperSpecialStruct
{
public int field1;
[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 256)]
public string field2;
[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 20)]
public string field3;
[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 10)]
public string field4;
public ushort field5;
public ushort field6;
public ushort field7;
public short field8;
public short field9;
public uint field10;
public short field11;
};
C++:
short SuperSpecialOpenFileFunc(SuperSpecialStruct * stuff);
struct SuperSpecialStruct
{
int field1;
char field2[256];
char field3[20];
char field4[10];
unsigned short field5;
unsigned short field6;
unsigned short field7;
short field8;
short field9;
unsigned int field10;
short field11;
};
Here is the error:
Managed Debugging Assistant
'PInvokeStackImbalance' has detected a
problem in 'Managed application path'.
Additional Information: A call to
PInvoke function
'SuperSpecialOpenFileFunc' has
unbalanced the stack. This is likely
because the managed PInvoke signature
does not match the unmanaged target
signature. Check that the calling
convention and parameters of the
PInvoke signature match the target
unmanaged signature.
As mentioned in Dane Rose's comment, you can either use __stdcall on your C++ function or declare CallingConvention = CallingConvention.Cdecl on your DllImport.
You specify stdcall in C# but not in C++, a mismatch here will lead to both the function and the caller popping arguments off of the stack.
On the other hand there is a compiler switch that will turn on stdcall as the default calling convention, (-Gz) are you using that?
Or try this in your C++
short __stdcall SuperSpecialOpenFileFunc(SuperSpecialStruct * stuff);
You specify no padding in your C# declaration of the struct, but not in the C++ version. Since you are mixing char arrays that are not all multiples of four and an odd number of 2 byte shorts, the compiler is probably inserting padding within the struct and add the end.
Try wrapping the struct in a #pragma pack to ensure no padding.
#pragma pack(push)
#pragma pack(1)
// The struct
#pragma pack(pop)
Had the same problem as described - unmanaged C++ app that has worked perfectly for years. When we upgraded to VS2010, we started getting PInvokeStackUnbalanced messages.
adding "__stdcall" to the C++ signature as described above made the issue go away.
It's good.I update function define as follow:
[DllImport("mydll.dll", CallingConvention = CallingConvention.Cdecl)]
It works well.