Develop Reference

Passing an array of strings from C++ to C#

I've already written this piece of code which works fine:
C++ code
extern "C"
{
const MYLIBRARY_EXPORT char* giefStrPlx(char* addon)
{
return addon;
}
}
C# code
[DllImport("ClassLibrary1")]
private static extern IntPtr giefStrPlx(string x);
void Start()
{
IntPtr stringPtr = giefStrPlx("Huntsman");
string huntsman = Marshal.PtrToStringAnsi(echoedStringPtr);
}
After this huntsman contains "Huntsman".
My problem is the step of doing something similar for an array of strings. I wrote the following function
extern "C"
{
const MYLIBRARY_EXPORT bool fillStrArray(char** lizt, int* length)
{
char* one = "one";
char* two = "two";
char* three = "three";
lizt[0] = one;
lizt[1] = two;
lizt[2] = three;
*length = 3;
}
}
I then tried to write the following piece of code in C#
[DllImport("ClassLibrary1")]
private static extern bool fillStrArray(ref IntPtr array, ref int length);
void Start()
{
IntPtr charArray = IntPtr.Zero;
int charArraySize = 0;
fillStrArray(ref charArray, ref charArraySize);
IntPtr[] results = new IntPtr[charArraySize];
Marshal.Copy(charArray, results, 0, charArraySize);
foreach (IntPtr ptr in results)
{
string str = Marshal.PtrToStringAnsi(ptr);
}
}
Which does not work. So now I'm a bit lost on how to accomplish this.

Here are the two helper functions I have from CLR to std::string and from std::string to string CLR
std::string CLROperations::ClrStringToStdString(String^ str)
{
if (String::IsNullOrEmpty(str))
return "";
std::string outStr;
IntPtr ansiStr = System::Runtime::InteropServices::Marshal::StringToHGlobalAnsi(str);
outStr = (const char*)ansiStr.ToPointer();
System::Runtime::InteropServices::Marshal::FreeHGlobal(ansiStr);
return outStr;
}
String ^ CLROperations::StdStringToClr(std::string str)
{
return gcnew String(str.c_str());
}
for using a List of strings you will need to use List<String^>^ mind the capital String. for a list of std::string use std::vector<std::string>

Convert IntPtr to char** in C#

I'd like to interpret the output of the following unmanaged function:
afc_error_t afc_get_device_info (afc_client_t client, char ***device_information)
I import the dll with the code:
[DllImport("libimobiledevice.dll", CallingConvention = CallingConvention.Cdecl)]
internal static extern short afc_get_device_info(IntPtr client, out IntPtr info);
As long as I only needed to convert response to string Marshal.PtrToStringAnsi was okay. However I have no idea how to convert that IntPtr back to char array.

It should be something like:
IntPtr di;
int result = afc_read_directory(client, #"C:\", out di);
if (di == IntPtr.Zero)
{
throw new Exception();
}
IntPtr di2 = di;
while (true)
{
IntPtr ptr = Marshal.ReadIntPtr(di2);
if (ptr == IntPtr.Zero)
{
break;
}
string str = Marshal.PtrToStringAnsi(ptr);
if (str == string.Empty)
{
break;
}
di2 = di2 + IntPtr.Size;
}
Try if it works, then I'll explain how...
important you are leaking memory here...
I've found this example in C:
char **dirs = NULL;
afc_read_directory(afc, "/eafaedf", &dirs);
if (!dirs)
afc_read_directory(afc, "/", &dirs);
printf("Directory time.\n");
for (i = 0; dirs[i]; i++) {
printf("/%s\n", dirs[i]);
free(dirs[i]);
}
if (dirs)
free(dirs);
you are responsible for freeing the memory (see the free inside the cycle and the final free?). In this case (and for other methods that return arrays of C-strings you can use afc_dictionary_free. Note that other methods like afc_receive_data that return a single block of memory you can't use it.

Implementing a custom collation in SQLite for WinRT

I'm trying to implement a custom collation in SQLite for Windows Runtime.
The create_collation method is implemented as follows:
SQLITE_API int sqlite3_create_collation(
sqlite3*,
const char *zName,
int eTextRep,
void *pArg,
int(*xCompare)(void*,int,const void*,int,const void*)
);
So far I have the following C# signature:
[DllImport("sqlite3", EntryPoint = "sqlite3_create_collation", CallingConvention = CallingConvention.Cdecl)]
public static extern int CreateCollation(IntPtr db, [MarshalAs(UnmanagedType.LPStr)] string name, int textRep, object state, Compare callback);
public delegate int Compare(object pCompareArg, int size1, IntPtr Key1, int size2, IntPtr Key2);
This is the implementation:
int i = CreateCollation(db, "unicode_nocase", SQLITE_UTF8, null, CompareMethod);
/* ... */
public static int CompareMethod(object o, int i1, IntPtr s1, int i2, IntPtr s2)
{
return string.Compare(Marshal.PtrToStringUni(s1), Marshal.PtrToStringUni(s2));
}
The application compiles without errors. The call to create_collation returns zero (SQLITE_OK), but if I use the collation in a statement the following error message is returned:
no such collation sequence: unicode_nocase
source reference: https://github.com/doo/SQLite3-WinRT/tree/master/SQLite3Component
Can somebody please help me?
Thank you!

After some time looking around inside Mono.Android.SQLite, which also uses the C implementation of SQLite, I found the solution:
The problem was that the call to sqlite3_create_collation has a void* parameter which I incorrectly defined as object in C# where it should be IntPtr.
I have posted the current implementation I have below. I partially reverse engineered the solution from the Mono implementation, which calls sqlite3_create_collation twice for every collation to be registered - once with the parameter eTextRep set to SQLITE_UTF16LE and a second time with SQLITE_UTF8. I could only imagine that this might help the SQLite core to find a fast implementation for different formats in which the string values are stored. However, these require different decoding when they are converted to C# strings.
[UnmanagedFunctionPointer(CallingConvention.Cdecl)]
private delegate int CompareCallback(IntPtr pvUser, int len1, IntPtr pv1, int len2, IntPtr pv2);
[DllImport("sqlite3", CallingConvention = CallingConvention.Cdecl)]
private static extern int sqlite3_create_collation(IntPtr db, byte[] strName, int nType, IntPtr pvUser, CompareCallback func);
private const int SQLITE_UTF8 = 1;
private const int SQLITE_UTF16LE = 2;
private const int SQLITE_UTF16BE = 3;
private const int SQLITE_UTF16 = 4; /* Use native byte order */
private const int SQLITE_ANY = 5; /* sqlite3_create_function only */
private const int SQLITE_UTF16_ALIGNED = 8; /* sqlite3_create_collation only */
public void Register(IntPtr db)
{
if (db == IntPtr.Zero)
throw new ArgumentNullException("db");
//create null-terminated UTF8 byte array
string name = Name;
var nameLength = System.Text.Encoding.UTF8.GetByteCount(name);
var nameBytes = new byte[nameLength + 1];
System.Text.Encoding.UTF8.GetBytes(name, 0, name.Length, nameBytes, 0);
//register UTF16 comparison
int result = sqlite3_create_collation(db, nameBytes, SQLITE_UTF16LE, IntPtr.Zero, CompareUTF16);
if (result != 0)
{
string msg = SQLite3.GetErrmsg(db);
throw SQLiteException.New((SQLite3.Result)result, msg);
}
//register UTF8 comparison
result = sqlite3_create_collation(db, nameBytes, SQLITE_UTF8, IntPtr.Zero, CompareUTF8);
if (result != 0)
{
string msg = SQLite3.GetErrmsg(db);
throw SQLiteException.New((SQLite3.Result)result, msg);
}
}
private string GetUTF8String(IntPtr ptr, int len)
{
if (len == 0 || ptr == IntPtr.Zero)
return string.Empty;
if (len == -1)
{
do
{
len++;
}
while (Marshal.ReadByte(ptr, len) != 0);
}
byte[] array = new byte[len];
Marshal.Copy(ptr, array, 0, len);
return Encoding.UTF8.GetString(array, 0, len);
}
private string GetUTF16String(IntPtr ptr, int len)
{
if (len == 0 || ptr == IntPtr.Zero)
return string.Empty;
if (len == -1)
{
return Marshal.PtrToStringUni(ptr);
}
return Marshal.PtrToStringUni(ptr, len / 2);
}
internal int CompareUTF8(IntPtr ptr, int len1, IntPtr ptr1, int len2, IntPtr ptr2)
{
return Compare(GetUTF8String(ptr1, len1), GetUTF8String(ptr2, len2));
}
internal int CompareUTF16(IntPtr ptr, int len1, IntPtr ptr1, int len2, IntPtr ptr2)
{
return Compare(GetUTF16String(ptr1, len1), GetUTF16String(ptr2, len2));
}

Return C++ char to C#

I have a C++ project in which I have to return some variables from C++ to C#.
These char variables are in the main program:
char test1[MAX_Q_LEN], test2[MAX_Q_LEN], test3[MAX_Q_LEN];
After I finish doing something with these variables in my C program, I have to return the values of these variables in a C# program.
ReturnChar.h
extern "C" RETURNCHAR_API TCHAR* __cdecl testString();
ReturnChar.cpp
extern "C" RETURNCHAR_API TCHAR* testString()
{
return ;
}
TestImport C#
static class TestImport
{
[DllImport("MyDLL.dll", CallingConvention = CallingConvention.Cdecl)]
private static extern IntPtr testString();
}
public partial class MainWindow : Window
{
public MainWindow()
{
try
{
InitializeComponent();
textBox1.Text = ReturnSomething()
}
catch (Exception ex)
{
MessageBox.Show(ex.ToString());
}
}
private static string ReturnSomething()
{
IntPtr t = TestImport.testString();
String result = Marshal.PtrToStringAuto(t);
}
I tried with the above approach but I am not able to find out how to return the above char values. Also, this should not be an independent function because the values shoud be fetched only after executing the main which will give the right values in these variables.
Any suggestions?

I will suggest a solution which would require you to change function signature to this:
extern "C" int __cdecl testString(char *output, int outputSize);
That is, pass an allocated buffer as the first argument to the function which will hold the output, and pass the size of the buffer as the second argument.
Note that I mention the return type of the function as int. It is because you could return the output actual size from the function, and the caller can interpret this value to confirm that outputSize value was large enough to hold the output string. For example, you could implement testString() as:
int testString(char *output, int outputSize)
{
std::string const & s = getString();
if ( s.size() <= outputSize )
{
std::strncpy(output, s.c_str(), s.size());
return s.size(); //return the actual size of output
}
else //means s.size() > outputSize, i.e outputSize is smaller than required!
{
std::strncpy(output, s.c_str(), outputSize);
return s.size(); //return what is required (the actual size of output)!
}
}
Then in C# code, do this:
[DllImport("MyDLL.dll", CallingConvention = CallingConvention.Cdecl)]
private static extern int testString(out StringBuilder output, int outputSize);
And call it as:
private static string ReturnSomething()
{
int bufferSize = 100;
StringBuilder buffer= new StringBuilder(bufferSize);
int outputSize = TestImport.testString(buffer, bufferSize);
if ( outputSize < bufferSize ) //output bufferSize was sufficient
{
return buffer.ToString();
}
else //output bufferSize was insufficient
{
//retry!
bufferSize = outputSize;
buffer = new StringBuilder(bufferSize); //reallocate!
outputSize = TestImport.testString(buffer, bufferSize);
if ( outputSize <= bufferSize )
return buffer.ToString();
else
{
throw new Exception("PANIC");
}
}
}

I'm not quite big c++ spec, but maybe to use bstrs in c++
_bstr_t text("saasas");
return text.Detach();
and for c# parameter
[MarshalAs(UnmanagedType.BStr)]
or to pass StringBuilder to your c++ func with some preallocated capacity

Pinvoke C# from C++ dll using DLLimport in C#

C++ Function header in DLL this two function to get some information about the wifi stations around me using win mobile 6.5 device and i need to invoke them to use them in C# code
// (adapter names , pointer to destination buffer ,and the size , returned structs)
bool __declspec(dllexport) GetBBSIDs(LPWSTR pAdapter, struct BSSIDInfo *pDest, DWORD &dwBufSizeBytes, DWORD &dwReturnedItems);
bool __declspec(dllexport) RefreshBSSIDs(LPWSTR pAdapter);
bool __declspec(dllexport) GetAdapters(LPWSTR pDest, DWORD &dwBufSizeBytes);
C# sample
[DllImport(#"\Storage Card\Work\Beaad.dll", EntryPoint = "GetAdapters", SetLastError = true)]
public static extern bool getAdapters([MarshalAs(UnmanagedType.LPWStr)] String buf, ref UInt32 dwBufSizeBytes);
[DllImport(#"\Storage Card\Work\Beaad.dll", EntryPoint = "RefreshBSSIDs", SetLastError = true)]
public static extern bool refreshBSSIDs([MarshalAs(UnmanagedType.LPWStr)]String buf);
[DllImport(#"\Storage Card\Work\Beaad.dll", EntryPoint = "GetBBSIDs", SetLastError = true)]
public static extern bool getBBSIDs([MarshalAs(UnmanagedType.LPWStr)]String buf,BSSIDInfo [] nfo, ref UInt32 dwBufSizeBytes, ref UInt32 dwReturnedItems);
[StructLayout(LayoutKind.Sequential,CharSet=CharSet.Auto)]
public struct BSSIDInfo
{
public byte[] BSSID; //mac
public char[] SSID;
public BSSIDInfo(byte[]bs,char[] ss)
{
this.RSSI = 0;
this.Infastructure = 0;
this.Channel = 0;
this.Auth = 0;
bs = new byte[6];
ss = new char[32];
BSSID = bs;
SSID = ss;
}
public int RSSI;
public int Channel;
public int Infastructure;
public int Auth;
}
public static byte[] StrToByteArray(string str)
{
System.Text.UTF8Encoding encoding = new System.Text.UTF8Encoding();
return encoding.GetBytes(str);
}
public static char[] c = new char[1024];
string buf = new string(c);
public void button1_Click(object sender, EventArgs e)
{
BSSIDInfo[] nfo = new BSSIDInfo[128];
byte[] bytee=StrToByteArray(buf);
UInt32 dwsize= new UInt32();
UInt32 dwTmp = new UInt32();
UInt32 dwCount = new UInt32();
dwTmp = Convert.ToUInt32(Marshal.SizeOf(typeof(BSSIDInfo)) * nfo.Length);
dwCount =0;
dwsize=Convert.ToUInt32(bytee.Length);
if (false == getAdapters(buf,ref dwsize) || dwsize == 0)
{
label1.Text = "no adabters";
}
else
{
String [] strList=new String[15];
if (buf.Contains(',') == false)// one adapter
{
textBox1.Text = buf;
}
else
{
strList = buf.Split(',');
for (int i = 0; i < strList.Length; i++)
{
textBox1.Text+= strList[i]+Environment.NewLine;
}
}
if (refreshBSSIDs(buf) && getBBSIDs(buf, nfo, ref dwTmp, ref dwCount) && dwCount > 0)
{
//refreshBSSIDs(buf) &&
for (int i = 0; i < dwCount; i++)
{
textBox2.Text += nfo.GetValue(i).ToString() + Environment.NewLine;
}
}
else
{
//make another thing
}
}
}
and when i put this dll on the mobile and the C# app.exe the first function that named as Getadapters(..) return to me the name of the adapter in the first textbox1 then the app stopped and give me not supported exception when the mobile tries to execute the other two function that named as refreshBSSID() and getBSSIDs() so what is the problem ? or is there another solution to get this information (BSSID ,SS ..etc) ?

C++ by default unless changed uses a caller( Cdecl ) calling convention. Your C++ code does not change the calling convention. Your C# code by default ( unless you change it ) will use a callee convention ( StdCall ).
While this might not be exactly the problem your having it still is technically incorrect. Even if you were to fix your current problem you likely will end up having a problem because of the calling convention.
I am going to guess your C# BSSIDInfo structure does not match the C++ structure. Why do the method StrToByteArray when all it does is GetBytes on the given string...
when the mobile tries to execute the
other two function that named as
refreshBSSID() and getBSSIDs() so what
is the problem ? or is there another
solution to get this information
I thought I knew the reason took another look and I was wrong.