I can't seem to figure out how to return an array from an exported C++ DLL to my C# program. The only thing I've found from googling was using Marshal.Copy() to copy the array into a buffer but that doesn't give me the values I'm trying to return, I don't know what it's giving me.
Here's what I've been trying:
Exported function:
extern "C" __declspec(dllexport) int* Test()
{
int arr[] = {1,2,3,4,5};
return arr;
}
C# portion:
[DllImport("Dump.dll")]
public extern static int[] test();
static void Main(string[] args)
{
Console.WriteLine(test()[0]);
Console.ReadKey();
}
I know the return type int[] is probably wrong because of the managed/unmanaged differences, I just have no idea where to go from here. I can't seem to find an answer for anything but returning character arrays to strings, not integer arrays.
I figured the reason the values I'm getting with Marshal.Copy are not the ones I'm returning is because the 'arr' array in the exported function gets deleted but I'm not 100% sure, if anyone can clear this up that would be great.
I have implemented the solution Sriram has proposed. In case someone wants it here it is.
In C++ you create a DLL with this code:
extern "C" __declspec(dllexport) int* test()
{
int len = 5;
int * arr=new int[len+1];
arr[0]=len;
arr[1]=1;
arr[2]=2;
arr[3]=3;
arr[4]=4;
arr[5]=5;
return arr;
}
extern "C" __declspec(dllexport) int ReleaseMemory(int* pArray)
{
delete[] pArray;
return 0;
}
The DLL will be called InteropTestApp.
Then you create a console application in C#.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Runtime.InteropServices;
namespace DLLCall
{
class Program
{
[DllImport("C:\\Devs\\C++\\Projects\\Interop\\InteropTestApp\\Debug\\InteropTestApp.dll")]
public static extern IntPtr test();
[DllImport("C:\\Devs\\C++\\Projects\\Interop\\InteropTestApp\\Debug\\InteropTestApp.dll", CallingConvention = CallingConvention.Cdecl)]
public static extern int ReleaseMemory(IntPtr ptr);
static void Main(string[] args)
{
IntPtr ptr = test();
int arrayLength = Marshal.ReadInt32(ptr);
// points to arr[1], which is first value
IntPtr start = IntPtr.Add(ptr, 4);
int[] result = new int[arrayLength];
Marshal.Copy(start, result, 0, arrayLength);
ReleaseMemory(ptr);
Console.ReadKey();
}
}
}
result now contains the values 1,2,3,4,5.
Hope that helps.
More or less the same as the answer above, but this worked for me.
For an array returned from a c method like this:
EXPORT char** methodname(void);
I did not succeed in getting this to work with the MarshalAs attribute, but this did the trick: (condensed code)
[DllImport(libName, EntryPoint = "methodname", CallingConvention = CallingConvention.Cdecl)]
public static extern IntPtr methodname();
var listPtr = methodname();
var list = new List<string>();
IntPtr itemPtr = IntPtr.Zero;
var offset = 0;
while ((itemPtr = Marshal.ReadIntPtr(listPtr, offset)) != IntPtr.Zero)
{
Console.WriteLine(Marshal.PtrToStringAnsi(itemPtr));
offset += 4;
}
Related
I have C# project and I have to use a C++ dll using DllImport. (I have source codes of c++ dll)
I'm importing a function from c++ dll like this :
[DllImport("Example.dll", CallingConvention = CallingConvention.StdCall)]
public static extern int SendRequest([MarshalAs(UnmanagedType.SafeArray, SafeArraySubType = VarEnum.VT_BSTR)] ref string[] fields);
I'm using this function in C# like this :
List<String> fields = new List<String>();
fields.Add("Test1");
fields.Add("Test2");
string[] fieldsArr = fields.ToArray();
int resultOfSendRequest = SendRequest(ref fieldsArr);
Problem is in c++ dll, it casts string to char* in somewhere and it reads the only first character, not entire string.
How can I solve this without touching c++ dll. (If I call this function from VB6 it works without any problem.)
C++ code is like this :
VARIANT vVar;
__declspec( dllexport ) int _stdcall SendRequest (SAFEARRAY**);
int _stdcall SendRequest ( SAFEARRAY** arrayFlds,
short NFlds)
{
// *********** prepare O.i.d, fields name, values
for (long iElem=0; iElem < NFlds; iElem++)
if (LoadElement (&vVar, iElem, &flds[iElem], &pFlds[iElem],*arrayFlds)==-1)
return -1;
//...
}
int LoadElement( VARIANT* vVar,
long iElem,
S_FLDS* flds,
char** pFld,
SAFEARRAY* arrayFlds)
{
hRes = SafeArrayGetElement(arrayFlds, &iElem, pFld);
strcpy(flds->FieldName, *pFld);
flds->bValLen = 0;
char *Name = flds->FieldName;
//....
}
The fieldName and char *Name at the end of the core only consists of first character of string. Not the full string.
In C Langues a string is a byte[] with each string terminated with a '\0'. An array of strings the last item has two '\0' at the end. So try following :
[DllImport("Example.dll", CallingConvention = CallingConvention.StdCall)]
public static extern int SendRequest(IntPtr fields);
static void Main(string[] args)
{
List<String> fields = new List<String>();
fields.Add("Test1");
fields.Add("Test2");
string fieldsArr = string.Join("\0", fields);
IntPtr fieldsPtr = Marshal.StringToBSTR(fieldsArr);
int results = SendRequest(fieldsPtr);
}
If it is an array of pointers then use this
public struct Pointers
{
public IntPtr[] pointers;
}
[DllImport("Example.dll", CallingConvention = CallingConvention.StdCall)]
public static extern int SendRequest(IntPtr fields);
static void Main(string[] args)
{
List<String> fields = new List<String>();
fields.Add("Test1");
fields.Add("Test2");
List<IntPtr> pointers = new List<IntPtr>();
foreach (string field in fields)
{
IntPtr intPtr = Marshal.StringToBSTR(field);
pointers.Add(intPtr);
}
Pointers sPointers = new Pointers();
sPointers.pointers = pointers.ToArray();
IntPtr fieldsPtr = IntPtr.Zero;
Marshal.StructureToPtr(sPointers, fieldsPtr, true);
int results = SendRequest(fieldsPtr);
Marshal.FreeHGlobal(fieldsPtr);
}
I am implementing a C++ Dll for C#. But when I run my program, an AccessViolationException will occur. Here is the code.
in C++:
extern "C" DLLIMPORT double __cdecl ErrorCalculate(double* pBufferA, double* pBufferB,__int32 length)
{
__m128d xfdLoadA;
__m128d xfdLoadB;
const double* pA = pBufferA;
const double* pB = pBufferB;
//do somthing
for(int i=0;i<length/2;i++)
{
xfdLoadA = _mm_load_pd(pA);//error occur at this line
xfdLoadB = _mm_load_pd(pB);
pA+=2;
pB+=2;
// do somthing
}
// do somthing
}
in C#:
[DllImport("test.dll", EntryPoint = "ErrorCalculate", CallingConvention = CallingConvention.Cdecl)]
static extern double ErrorCalculate(double[] pBufferA, double[] pBufferB, int length);
public void frameProcessing(Image<Gray, byte> frame){
//do something
SSE4 sse4 = new SSE4();
unsafe
{
//length of samplePoint is the same as tempPoint
fixed (double* sample = samplePoint)
{
fixed (double* test = tempPoint)
{
errorSum = sse4.ErrorCalc(sample, test, length);
}
}
}
if(errorSum<=threshold)
{//do something}
}
frameProcessing will be called several times. Sometimes the error will occur at first time I call frameProcessing, sometimes second time. And I found that error occur at _mm_load_pd(pA). I'm sure that pA and pB are not null(Value of the two array can be printed out). Any help would be appreciated.
I want to use Ghostscript in a .NET / C# application to convert a .tiff file to PDF.
My problem: When the file path contains non-ansi characters (e.g. Umlaute), the function
gsapi_init_with_args
fails. (With GS 8.x, it works fine!).
I found information that the behaviour was changed in 9.x, and I also found a function called
gsapi_init_with_argsW
And this function should work with .NET without any problems (see http://permalink.gmane.org/gmane.comp.printing.ghostscript.cvs/31721)
So I use the following DLLImport:
[DllImport(#"gsdll32.dll")]
public static extern int gsapi_init_with_argsW( IntPtr instace, int argc, string[] argv);
but this still does not work, I get the error:
Error: /undefinedfilename
in (C:\\304NDERUNGEN\\TEST.PDF)
The name of the file schould be
C:\\ÄNDERUNGEN\\TEST.PDF
so the umlaut "Ä" is not recognized correctly.
I´ve search the web a lot but did not found a solution.
Any idea?
Thank you!
I suspect that you will need to use UTF-8 here. Make a call to gs_set_arg_encoding passing GS_ARG_ENCODING_UTF8.
Any strings that you pass to Ghostscript should be declared as IntPtr. To convert from a C# string to a null-terminated UTF-8 encoded string use this function provided by Hans Passant:
public static IntPtr NativeUtf8FromString(string managedString)
{
int len = Encoding.UTF8.GetByteCount(managedString);
byte[] buffer = new byte[len + 1]; // null-terminator allocated
Encoding.UTF8.GetBytes(managedString, 0, managedString.Length, buffer, 0);
IntPtr nativeUtf8 = Marshal.AllocHGlobal(buffer.Length);
Marshal.Copy(buffer, 0, nativeUtf8, buffer.Length);
return nativeUtf8;
}
Make sure that you remember to clean up with a call to Marshal.FreeHGlobal.
The overall code might look a little like this:
public class Ghostscript
{
public const int GS_ARG_ENCODING_LOCAL = 0;
public const int GS_ARG_ENCODING_UTF8 = 1;
[DllImport("gsdll32.dll")]
private static extern int gsapi_new_instance(out IntPtr inst, IntPtr handle);
[DllImport("gsdll32.dll")]
private static extern int gsapi_set_arg_encoding(IntPtr inst, int encoding);
[DllImport("gsdll32.dll")]
private static extern int gsapi_init_with_args(IntPtr inst, int argc, IntPtr[] argv);
[DllImport("gsdll32.dll")]
private static extern int gsapi_exit(IntPtr inst);
[DllImport("gsdll32.dll")]
private static extern void gsapi_delete_instance(IntPtr inst);
private static void checkReturnValue(int retval)
{
if (retval != 0)
throw ...; // implement error handling here
}
public static void run(string[] argv)
{
IntPtr inst;
checkReturnValue(gsapi_new_instance(out inst, IntPtr.Zero));
try
{
IntPtr[] utf8argv = new IntPtr[argv.length];
for (int i=0; i<utf8argv.Length; i++)
utf8argv[i] = NativeUtf8FromString(argv[i]);
try
{
checkReturnValue(gsapi_set_arg_encoding(inst, GS_ARG_ENCODING_UTF8));
checkReturnValue(gsapi_init_with_args(inst, utf8argv.Length, utf8argv));
checkReturnValue(gsapi_exit(inst));
finally
{
for (int i=0; i<utf8argv.Length; i++)
Marshal.FreeHGlobal(utf8argv[i]);
}
}
finally
{
gsapi_delete_instance(inst);
}
}
}
Could you guys please help me solve the following issue?
I have a C++ function dll, and it will be called by another C# application.
One of the functions I needed is as follow:
struct DataStruct
{
unsigned char* data;
int len;
};
DLLAPI int API_ReadFile(const wchar_t* filename, DataStruct** outData);
I wrote the following code in C#:
class CS_DataStruct
{
public byte[] data;
public int len;
}
[DllImport("ReadFile.dll", CallingConvention = CallingConvention.Cdecl, CharSet = CharSet.Unicode)]
private static extern int API_ReadFile([MarshalAs(UnmanagedType.LPWStr)]string filename, ref CS_DataStruct data);
Unfortunately, the above code is not working... I guess that is due to the C++ func takes a pointer-to-pointer of DataStruct, while I just passed a reference of CS_DataStruct in.
May I know how can I pass a pointer-to-pointer to the C++ func? If it is not possible, is there any workaround? (the C++ API is fixed, so changing API to pointer is not possible)
Edit:
Memory of DataStruct will be allocated by c++ function. Before that, I have no idea how large the data array should be.
(Thanks for the comments below)
I used the following test implementation:
int API_ReadFile(const wchar_t* filename, DataStruct** outData)
{
*outData = new DataStruct();
(*outData)->data = (unsigned char*)_strdup("hello");
(*outData)->len = 5;
return 0;
}
void API_Free(DataStruct** pp)
{
free((*pp)->data);
delete *pp;
*pp = NULL;
}
The C# code to access those functions are as follows:
[StructLayout(LayoutKind.Sequential)]
struct DataStruct
{
public IntPtr data;
public int len;
};
[DllImport("ReadFile.dll", CallingConvention = CallingConvention.Cdecl, CharSet = CharSet.Unicode)]
unsafe private static extern int API_ReadFile([MarshalAs(UnmanagedType.LPWStr)]string filename, DataStruct** outData);
[DllImport("ReadFile.dll", CallingConvention = CallingConvention.Cdecl)]
unsafe private static extern void API_Free(DataStruct** handle);
unsafe static int ReadFile(string filename, out byte[] buffer)
{
DataStruct* outData;
int result = API_ReadFile(filename, &outData);
buffer = new byte[outData->len];
Marshal.Copy((IntPtr)outData->data, buffer, 0, outData->len);
API_Free(&outData);
return result;
}
static void Main(string[] args)
{
byte[] buffer;
ReadFile("test.txt", out buffer);
foreach (byte ch in buffer)
{
Console.Write("{0} ", ch);
}
Console.Write("\n");
}
The data is now transferred to buffer safely, and there should be no memory leaks. I wish it would help.
It isn't necessary to use unsafe to pass a pointer to an array from a DLL. Here is an example (see the 'results' parameter). The key is to use the ref attribute. It also shows how to pass several other types of data.
As defined in C++/C:
#ifdef __cplusplus
extern "C" {
#endif
#ifdef BUILDING_DLL
#define DLLCALL __declspec(dllexport)
#else
#define DLLCALL __declspec(dllimport)
#endif
static const int DataLength = 10;
static const int StrLen = 16;
static const int MaxResults = 30;
enum Status { on = 0, off = 1 };
struct Result {
char name[StrLen]; //!< Up to StrLen-1 char null-terminated name
float location;
Status status;
};
/**
* Analyze Data
* #param data [in] array of doubles
* #param dataLength [in] number of floats in data
* #param weight [in]
* #param status [in] enum with data status
* #param results [out] array of MaxResults (pre-allocated) DLLResult structs.
* Up to MaxResults results will be returned.
* #param nResults [out] the actual number of results being returned.
*/
void DLLCALL __stdcall analyzeData(
const double *data, int dataLength, float weight, Status status, Result **results, int *nResults);
#ifdef __cplusplus
}
#endif
As used in C#:
private const int DataLength = 10;
private const int StrLen = 16;
private const int MaxThreatPeaks = 30;
public enum Status { on = 0, off = 1 };
[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
public struct Result
{
[MarshalAs(UnmanagedType.ByValTStr, SizeConst = StrLen)] public string name; //!< Up to StrLen-1 char null-terminated name
public float location;
public Status status;
}
[DllImport("dllname.dll", CallingConvention = CallingConvention.StdCall, EntryPoint = "analyzeData#32")] // "#32" is only used in the 32-bit version.
public static extern void analyzeData(
double[] data,
int dataLength,
float weight,
Status status,
[MarshalAs(UnmanagedType.LPArray, SizeConst = MaxResults)] ref Result[] results,
out int nResults
);
Without the extern "C" part, the C++ compiler would mangle the export name in a compiler dependent way. I noticed that the EntryPoint / Exported function name matches the function name exactly in a 64-bit DLL, but has an appended '#32' (the number may vary) when compiled into a 32-bit DLL. Run dumpbin /exports dllname.dll to find the exported name for sure. In some cases you may also need to use the DLLImport parameter ExactSpelling = true. Note that this function is declared __stdcall. If it were not specified, it would be __cdecl and you'd need CallingConvention.Cdecl.
Here is how it might be used in C#:
Status status = Status.on;
double[] data = { -0.034, -0.05, -0.039, -0.034, -0.057, -0.084, -0.105, -0.146, -0.174, -0.167};
Result[] results = new Result[MaxResults];
int nResults = -1; // just to see that it changes (input value is ignored)
analyzeData(data, DataLength, 1.0f, status, ref results, out nResults);
If you do call native code, make sure your structs are alligned in the memory. CLR does not guarantee alignment unless you push it.
Try
[StructLayout(LayoutKind.Explicit)]
struct DataStruct
{
string data;
int len;
};
More info:
http://www.developerfusion.com/article/84519/mastering-structs-in-c/
I have this in my dll created in c++
extern "C" __declspec(dllexport)
char* __stdcall hh()
{
char a[2];
a[0]='a';
a[1]='b';
return(a);
}
And this is how I am trying to handle code in c#
[DllImport(#"mydll.dll",CharSet = CharSet.Ansi,CallingConvention = CallingConvention.StdCall)]
public static extern IntPtr hh();
static void Main(string[] args)
{
IntPtr a = hh();
//How to proceed here???
}
}
Help in proceeding further.
There is no way to handle such arrays. char a[2] is allocated on the stack in your C++ function and is destroyed as soon as you return from it. You should either pass an array from C# and fill it in the C++ code or allocate array in the heap and provide some means for freeing it.
When you have it correct the handling will depend on how you return the data from C++ code. If it's still IntPtr you could use Marshal.ReadByte methods to read characters from memory and use Encoding methods to convert those bytes into string if necessary.
const int bufferSize = 2; // suppose it's some well-known value.
IntPtr p = ...; // get this pointer somehow.
for (var i = 0; i != bufferSize; ++i)
{
var b = Marshal.ReadByte(p, i);
Console.WriteLine(b);
}
I got a solution as follows::
OUR C++ code goes as follows
extern "C" __declspec(dllexport)
char** __stdcall hh()
{
static char* myArray[3] = {"A1", "BB2", "CC3",};
return myArray;
}
And C# goes as follows
[DllImport(#"ourdll.dll",CharSet = CharSet.Ansi,CallingConvention = CallingConvention.StdCall)]
public static extern IntPtr hh();
static void Main(string[] args)
{
IntPtr a = hh();
int j = 0;
string[] s=new string[100];
do
{
s[j] = Marshal.PtrToStringAnsi(Marshal.ReadIntPtr(a,4*j));
j++;
}
while(s[j-1] != null);
}
The only problem now faced is that how can we know size of the array
so that in this statement
string[] s=new string[100];
we neednot waste our memory.
The answer would be
string stra = Marshal.PtrToStringAnsi(a);
But you also have the problem that the dll returns garbage per your code as char* is a local c style string.
Would be ok if you would return something like:
const char* str = "Hello from DLL.";
Try to use not empty StringBuilder as the return value.