I have an API that takes three parameters
BOOL GetServerName (int index, LPSTR Buffer, int BufSize);
how can i use this method in C#
What is the equivalence of LPSTR ?
[DllImport("YourDll.dll", CharSet = CharSet.Ansi)]
//[return: MarshalAs(UnmanagedType.Bool)] // This line is optional, and it's implicit
static extern bool GetServerName(int index, StringBuilder buffer, int bufSize);
To use it:
int bufSize = 100;
StringBuilder buffer = new StringBuilder(bufSize);
bool result = GerServerName(0, buffer, bufSize);
if (result)
{
string buffer2 = buffer.ToString();
}
Technically your question was "what is equivalent to LPSTR"... The response is: string or StringBuilder if you are passing the string to the method, StringBuilder if the method is passing the string to you. Another alternative is using a byte[] and doing the Encoding/Decoding yourself, like:
[DllImport("YourDll.dll", CharSet = CharSet.Ansi)]
//[return: MarshalAs(UnmanagedType.Bool)] // This line is optional, and it's implicit
static extern bool GetServerName(int index, byte[] buffer, int bufSize);
and
int bufSize = 100;
byte[] buffer = new byte[bufSize];
bool result = GerServerName(0, buffer, bufSize);
if (result)
{
string buffer2 = Encoding.Default.GetString(buffer, 0, Array.IndexOf(buffer, (byte)0));
}
(C string are null terminated. We find the first \0 with Array.IndexOf(buffer, (byte)0) and we convert the characters up to the null to a string with Encoding.Default.GetString()).
Some comments...
I hope you have the maximum length of buffer (like a constant), because normally these methods are written as returning in some way the length of the string.
If you have an Unicode version of the method (perhaps GetServerNameW), you should use it. It's better to use Unicode methods if present, so non-Ansi characters aren't lost.
As a sidenote, when you use DllImport, you should check if you are using the correct calling convention. For Windows API you don't need to do anything, but depending on how the method has been defined in the header file, you could need to add CallingConvention = CallingConvention.something). Often (but now always) the .NET runtime will throw an exception on wrong calling convention, or the method won't work and will return strange things or will crash. This is because the calling convention tells the .NET how the parameters must be passed to the method (where, how, and who has to free the stack technically). Some examples of calling conventions in header files are cdecl, stdcall, fastcall, thiscall, pascal (equivalent to stdcall), WINAPI, APIENTRY (equivalent to WINAPI), CALLBACK (equivalent to WINAPI) and all of these words with _ or __ prepended or in all upper case.
The Microsoft VC++ normally uses the cdecl calling convention for C methods and the thiscall for C++ methods. You can control it through some arguments.
Related
I have native C++ dll with function that finds the number of cameras connected to the computer and returns their serial number. I am trying to use native C++ dll in C# application but I keep getting the Access Violation error(Attempted to read or write protected memory).
The function in question is
uint32_t GetSerialNumList(char** theBufList, int theBufSize, int theListLength);
The way I am using PInvoke is as follows:
[DllImport(CameraDll, EntryPoint = "GetSerialNumList", CallingConvention = CallingConvention.Cdecl)]
private static extern uint GetSerialNumList(out byte[] pBuf, int BufSize, int ListLength);
If I create native C++ application to use the dll and use the function as follows:
char* theSerialNumb;
theSerialNumb = (char *) malloc(sizeof(char)* 8);
status = TRI_GetSerialNumList(&theSerialNumb, 8, 1);
It works fine however, if I use as follows in C# it give me above mentioned error:
byte[] BufList;
BufList = new byte[8];
rv = GetSerialNumList(out BufList, 8, 1);
The parameter you're passing in c# is a pointer to a byte array. What you're passing in c++ is a pointer to a pointer to a byte array. Also, in the C++ example, you're passing data to the function, but in the C# example, you're passing it as an out instead of a ref.
Although I'm not sure this would work, I would try to create a struct containing a byte array and pass the struct to the external function.
To answer some of the above comments, these functions typically modify memory passed to it rather than try to allocate additional memory due to the different ways programs create heaps.
The first thing I'd check is the C# import signature being used. There's the P/Invoke Interop Assistant tool available for free here.
Loading your function signature into the tool, translates it to:
public partial class NativeMethods {
/// Return Type: unsigned int
///theBufList: char**
///theBufSize: int
///theListLength: int
[System.Runtime.InteropServices.DllImportAttribute("<Unknown>", EntryPoint="GetSerialNumList")]
public static extern uint GetSerialNumList(ref System.IntPtr theBufList, int theBufSize, int theListLength) ;
}
The second thing, is that since you are allocating memory for the buffer in the C++/native version; perhaps you need to pass a pre-allocated buffer as well, when using C#.
Hope this helps.
Okay, I took pointers from Russell and kvr and did some digging around and following is the scheme that I came up with.
Original native function call:
uint32_t GetSerialNumList(char** theBufList, int theBufSize, int theListLength);
The way I am using PInvoke is as follows:
[DllImport(CameraDll, EntryPoint = "GetSerialNumList", CallingConvention = CallingConvention.Cdecl)]
private static extern int GetSerialNumList(ref IntPtr pBuf, int BufSize, int ListLength);
byte[] BufIn;
BufIn = new byte[8 * ListLength];
IntPtr pBuf = IntPtr.Zero;
pBuf = Marshal.AllocHGlobal(8 * ListLength);
Console.WriteLine("Calling GetSerialNumList");
rv = GetSerialNumList(ref pBuf, 8, ListLength);
Marshal.Copy(pBuf, BufIn, 0, 8*ListLength);
I feel this is somewhat long, but it gives me the desired result.
I am trying to create a class in c# to access the function in a c++ lib. The function in the c++ dll :
bool WriteReply(const unsigned char *reply, const unsigned long reply_length).
A sample of how its used in c++:-
unsigned short msg_id = 0x0000;
byte msg_body[] = {(byte)(GetTickCount()/0x100)}; // a random value for loopback data
// combine the message id and message body into an big msg
unsigned long msg_length = sizeof(msg_id)+sizeof(msg_body);
byte* big_msg = new byte[msg_length];
big_msg[0] = LOBYTE(msg_id);
big_msg[1] = HIBYTE(msg_id);
memcpy((void*)&big_msg[2], (void*)msg_body, sizeof(msg_body));
// send the big message
if (!big_dev.WriteReply(big_msg, msg_length))
{
//do something here
}
I can't seem to pass the function from c# to the dll (AccessViolationException). This is the command i've tried:-
byte[] bytearray = new byte[3] { 0x01, 0x02, 0x03 };
IntPtr unmanagedPointer = Marshal.AllocHGlobal(bytearray.Length);
Marshal.Copy(bytearray, 0, unmanagedPointer, bytearray.Length);
bool writestatus = (bool)NativeMethods.WriteReply(unmanagedPointer, (uint)bytearray.Length);
and on the import side:-
[DllImport("dllname.dll", EntryPoint = "WriteReply")]
[return: MarshalAs(UnmanagedType.U1)]
internal static extern bool WriteReply(IntPtr msg, uint reply_length);
Please let me know where have i gone wrong?Thanks!
Assuming your C++ method uses the string and does not modify it...
Try this
__declspec(dllexport) bool __cdecl WriteReply(const unsigned char *reply, const unsigned long reply_length);
[DllImport("libfile.dll", EntryPoint = "WriteReply")]
private static extern bool WriteReplyExternal(
[MarshalAs(UnmanagedType.LPStr)] [Out] string replyString,
[Out] UInt32 replyLength);
Or better yet (since C strings are null-terminated and the buffer is readonly, so you don't have to worry about buffer overflow, the length parameter is redudant):
__declspec(dllexport) bool __cdecl WriteReply(const unsigned char *reply);
[DllImport("libfile.dll", EntryPoint = "WriteReply")]
private static extern bool WriteReplyExternal(
[MarshalAs(UnmanagedType.LPStr)] [Out] string replyString);
These will work if the method is not within a class, otherwise you will need to use the C++ mangled name as the entry point.
If your string contains characters outside the 1...127 ASCII range (e.g. non-English letters), you should use wchar_t instead of char in the C++ and LPWStr instead of LPStr in the marshalling.
Edit:
You need to wrap the private method with another method with a signature that is more appropriate for .NET e.g.
public void WriteReply(string message)
{
var result = WriteReplyExternal(message, message.Length);
if (result == false)
throw new ApplicationException("WriteReplay failed ...");
}
I think the latest addition of code provides a clue as to the real problem:
if (!big_dev.WriteReply(big_msg, msg_length))
This cannot work because WriteReply is an member function. You need to be calling a C style function rather than a C++ member function. The latter requires an instance (big_dev in the code sample).
I am new in microsoft world.
I have lot of problem trying to pass a simple string from c# to dll/c++
I have read a lot of post and documentation about but the problem is the same.
C++ code
extern "C" __declspec(dllexport) int Init( long l , char* url );
C# code
[DllImport("MCRenderer.dll", CharSet = CharSet.Ansi, SetLastError = true, ExactSpelling = false)]
public static extern int Init(long a, StringBuilder url);
Init(hndl.ToInt64(), str );
what haeppen is that long value is passed correctly while string parameter is
0x00000000 <Bad Ptr>
can you help me ... Iam really confused
thanks!!
AG
You should pass a string, url should be of type string and not StringBuilder.
It's because you're marshalling incorrectly: long and int in C++ are both (usually) int in C#.
From MSDN, you need to:
The only caveat is that the StringBuilder must be allocated enough space for the return value, or the text will overflow, causing an exception to be thrown by P/Invoke
Also from Marshaling between Managed and Unmanaged Code
Don't pass StringBuilder by reference (using out or ref). Otherwise, the CLR will expect the signature of this argument to be wchar_t ** instead of wchar_t *, and it won't be able to pin StringBuilder's internal buffer. Performance will be significantly degraded.
Use StringBuilder when the unmanaged code is using Unicode. Otherwise, the CLR will have to make a copy of the string and convert it between Unicode and ANSI, thus degrading performance. Usually you should marshal StringBuilder as LPARRAY of Unicode characters or as LPWSTR.
Always specify the capacity of StringBuilder in advance and make sure the capacity is big enough to hold the buffer. The best practice on the unmanaged code side is to accept the size of the string buffer as an argument to avoid buffer overruns. In COM, you can also use size_is in IDL to specify the size.
So in your example, you need to specify the native size as the parameter of the StringBuilder like this StringBuilder str = new StringBuilder(SIZE_OF_NATIVE_STRING);
Try using LPCSTR in the dll function parameter
extern "C" __declspec(dllexport) int Init( long l , **LPCTSTR** url );
Here is a good example that I found on how to do this.
C++:
extern "C" __declspec(dllexport) void doSomething(LPCTSTR asString)
{
std::cout << "here" << (wchar_t)asString << endl;
system ("pause");
}
C#:
class Program
{
static void Main(string[] args)
{
String myString = "String in C#";
doSomething(myString);
}
private const String path = #"C:\testdll2.dll"; //Make sure that the DLL is in this location
[DllImport(path)]
private static extern void doSomething(string asString);
}
I have created a win32 dll which sends and recieves ssl data packets from our server, I am calling a dll function using P/Invoke mechanism from my C# app which does all necessary tasks.
When I call Connect(char* lpPostData)
function and I use static char postData [] array as a posting request it works fine , if I use char* lpPostData as sent parameter from my C# app for posting request it doesn't works. Is it something with conversion of C# string to char * ?? if that is the case how do i do it ?? How to debug the in Win32 dll ???
Calling the exported function from C# app:
[DllImport("testdllwm6.dll", EntryPoint = "Connect")] public
static extern int pConnect(string postdata);
string postdata="<SyncML><SyncHdr><VerDTD>1.2</VerDTD><VerProto>SyncML/1.2</VerProto><SessionID>33622878</SessionID><MsgID>1</MsgID><Target><LocURI>http://sync.com</LocURI></Target><Source><LocURI>IMEI::358997011403172</LocURI><LocName>syncfdg</LocName></Source><Meta><MaxMsgSize
xmlns=\"syncml:metinf\">10000</MaxMsgSize></Meta></SyncHdr><SyncBody><Alert><CmdID>1</CmdID><Data>201</Data><Item><Target><LocURI>contacts</LocURI></Target><Source><LocURI>./contacts</LocURI></Source><Meta><Anchor
xmlns=\"syncml:metinf\"><Last>000000T000000Z</Last><Next>20091125T122400Z</Next></Anchor></Meta></Item></Alert><Final></Final></SyncBody></SyncML>";
int j = pConnect(postdata);
Declaration is:
__declspec(dllexport) int Connect(char* lpPostData);
The function is defined as:
__declspec(dllexport) int Connect(char* lpPostData) {
LPCTSTR lpszAgent = _T("CeHttp");
DWORD dwError; DWORD sizeInResult,
sizeOutResult, sizeToWrite,
sizeWritten,dwRead; HINTERNET
hInternet=NULL; HINTERNET
hConnect=NULL; HINTERNET
hRequest=NULL; LPDWORD
pSizeInResult = &sizeInResult;
LPDWORD pSizeOutResult = &sizeOutResult;
LPDWORD pSizeToWrite = &sizeToWrite;
LPDWORD pSizeWritten = &sizeWritten; int read = 0;
char postData[637]
="<SyncML><SyncHdr><VerDTD>1.2</VerDTD><VerProto>SyncML/1.2</VerProto><SessionID>66622878</SessionID><MsgID>1</MsgID><Target><LocURI>http://sync.com</LocURI></Target><Source><LocURI>IMEI::358997011403172</LocURI><LocName>new123</LocName></Source><Meta><MaxMsgSize
xmlns=\"syncml:metinf\">10000</MaxMsgSize></Meta></SyncHdr><SyncBody><Alert><CmdID>1</CmdID><Data>201</Data><Item><Target><LocURI>contacts</LocURI></Target><Source><LocURI>./contacts</LocURI></Source><Meta><Anchor
xmlns=\"syncml:metinf\"><Last>000000T000000Z</Last><Next>20091125T122400Z</Next></Anchor></Meta></Item></Alert><Final></Final></SyncBody></SyncML>";
LPCWSTR lpszHeaders =_T("Content-Type: application/vnd.sync+xml");
BOOL bResult;
if(!HttpSendRequest(hRequest,lpszHeaders,wcslen(lpszHeaders),
lpPostData,strlen(lpPostData)))
{
dwError = GetLastError();
printf(" not HttpSendRequest");
return read;
}
return read;
The failure point is very obvious. Windows CE is Unicode. The string in C# is a wide-character array, the char[] in C is a multibyte. You're mixing the two, and that is bad, bad, bad.
I mean you're mixing them in the same call, sending wide headers and multibyte postData to HttpSendRequest? That certainly can't be right.
Change the Connect function to look like this:
int Connect(TCHAR* lpPostData)
try it again, and come back with the results.
Of course this also means you need to change the strlen call as well.
As a side note, I don't understand why you would call into C++ for this call anyway. You could do it right from your C# app.
seems the dll is a MFC extension dll, maybe only can be callec by MFC application. i am not sure.
Is it something with conversion of C# string to char * ??
The default CharSet used by the .Net Interop Marshaler is Ansi.
If you want use Unicode(LPCWSTR) parameters,
you can try:
[DllImport("testdllwm6.dll", EntryPoint = "Connect", CharSet=CharSet.Unicode)]
public static extern int pConnect(string postdata);
BTW, you can refer to .Net 2.0 Interoperability Recipes: A Problem-Solution Approach
for more information.
You need to add the MarshalAs attribute to the string parameter so the .NET runtime knows how to marshal it; by default strings are marshaled as Unicode, but you want ANSI:
[DllImport("testdllwm6.dll", EntryPoint="Connect")]
public static extern int Connect([MarshalAs(UnmanagedType.LPStr)] string lpPostData);
use
System.Text.StringBuilder
pass that to your function
I have a C++ dll that I need to call from C#. One of the functions in the dll requires a char* for an input parameter, and another function uses a char* as an output parameter.
What is the proper way to call these from C#?
string should work if the parameter is read-only, if the method modifies the string you should use StringBuilder instead.
Example from reference below:
[DllImport ("libc.so")]
private static extern void strncpy (StringBuilder dest,
string src, uint n);
private static void UseStrncpy ()
{
StringBuilder sb = new StringBuilder (256);
strncpy (sb, "this is the source string", sb.Capacity);
Console.WriteLine (sb.ToString());
}
If you don't know how p/invoke marshaling works you could read http://www.mono-project.com/Interop_with_Native_Libraries
If you are only conserning with strings, read only the section: http://www.mono-project.com/Interop_with_Native_Libraries#Strings
Just using strings will work fine for input parameters, though you can control details about the string with the MarshalAs attribute. E.g.
[DllImport("somedll.dll", CharSet = CharSet.Unicode)]
static extern void Func([MarshalAs(UnmanagedType.LPWStr)] string wideString);
As for returning char* parameters, that's a little more complex since object ownership is involved. If you can change the C++ DLL you can use CoTaskMemAllocate, with something like:
void OutputString(char*& output)
{
char* toCopy = "hello...";
size_t bufferSize = strlen(toCopy);
LPVOID mem = CoTaskMemAlloc(bufferSize);
memcpy(mem, toCopy, bufferSize);
output = static_cast<char*>(mem);
}
The C# side then just uses an 'out string' parameter, and the garbage collector can pick up the ownership of the string.
Another way of doing it would be to use a StringBuilder, but then you need to know how big the string will be before you actually call the function.
Not sure this works, but have you tried with
StringObject.ToCharArray();
Not sure about initialising the String from char * tho. Mybe just assign to a string object, its worth a try.
Have you tried StringBuilder? I found this in a Google search:
[DllImport("advapi32.dll")]
public static extern bool GetUserName(StringBuilder lpBuffer, ref int nSize);
If you post the call you're making we can help you assemble it.
If the DLL function is expecting an allocated buffer of char* (not a wide/multibyte buffer) then the following will work:
[DllImport("somedll.dll", CharSet = CharSet.Ansi)]
static extern void TheFunc(byte[] someBuffer, int someSize);
Here a buffer allocated in c# is passed to TheFunc which fills it with a string of characters (of type char). Bytes aren't "interpreted" by C# they are treated like 8 bit integers, so are perfect for holding 8 bit characters.
An example code snipped would therefore be:
byte[] mybuffer;
int bufSize;
bufSize = 2048;
mybuffer = new byte[bufSize];
TheFunc(mybuffer, bufSize);
string value;
for(value = "", int ix = 0; (mybuffer[ix] != 0) && (ix < bufSize); ix++)
value += (char) mybuffer[ix];
DoSomethingWithTheReturnedString(value);