P/Invoke - Interoperability of C++ and C#
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This document provides a comprehensive overview of P/Invoke and its related concepts for interoperability between .NET and unmanaged code, including macros for exporting functions, memory handling, debugging techniques, and proper marshaling practices. It covers various topics such as calling conventions, character sets, memory management, and string marshaling, providing code examples and best practices. The content also highlights the importance of using Marshaling and the DOTNET interop services namespace effectively for seamless integration.
![// The following ifdef block is the standard way of creating macros which make exporting
// from a DLL simpler. All files within this DLL are compiled with the PINVOKE_EXPORTS
// symbol defined on the command line. This symbol should not be defined on any project
// that uses this DLL. This way any other project whose source files include this file see
// PINVOKE_EXPORTS functions as being imported from a DLL, whereas this DLL sees symbols
// defined with this macro as being exported.
#ifdef PINVOKE_EXPORTS
#define PINVOKE_API __declspec(dllexport)
#else
#define PINVOKE_API __declspec(dllimport)
#endif
DLL Exports
// Some quite simple functions to begin with
extern "C" PINVOKE_API int AddNumbers(int x, int y);
extern "C" PINVOKE_API int AddArray(int x[], int size);
// A very simple DLL export.
extern "C" PINVOKE_API int AddNumbers(int x, int y)
{
return x + y;
}
// A method taking an array.
extern "C" PINVOKE_API int AddArray(int x[], int size)
{
auto ans = 0;
for (int i = 0; i < size; i++)
{
ans += x[i];
}
return ans;
}
See also MSDN](https://image.slidesharecdn.com/pinvoke-140303132412-phpapp02/85/P-Invoke-Interoperability-of-C-and-C-3-320.jpg)
![// This works
extern "C" PINVOKE_API int __stdcall AddNumbers(int x, int y);
[DllImport("PInvokeIntroduction.dll")]
public static extern int AddNumbers(int x, int y);
// This works, too
extern "C" PINVOKE_API int AddNumbers(int x, int y);
[DllImport("PInvokeIntroduction.dll",
CallingConvention = CallingConvention.Cdecl)]
public static extern int AddNumbers(int x, int y);
// Anything else will throw an exception in the debugger
Calling Conventions](https://image.slidesharecdn.com/pinvoke-140303132412-phpapp02/85/P-Invoke-Interoperability-of-C-and-C-14-320.jpg)
![using System.Runtime.InteropServices;
namespace Samples.PInvoke.IntroductionClient
{
[StructLayout(LayoutKind.Sequential)]
public class Car
{
[MarshalAs(UnmanagedType.LPWStr)]
public string Make;
Character Sets
[MarshalAs(UnmanagedType.LPWStr)]
public string Color;
}
…
}
[DllImport("PInvokeIntroduction.dll",
CallingConvention = CallingConvention.Cdecl,
CharSet = CharSet.Unicode)]
public static extern void DisplayBetterCar(Car2 c);
See also MSDN](https://image.slidesharecdn.com/pinvoke-140303132412-phpapp02/85/P-Invoke-Interoperability-of-C-and-C-16-320.jpg)
![// Rename the MessageBoxW() function to 'DisplayMessage'.
[DllImport("user32.dll",
ExactSpelling = true,
CharSet = CharSet.Unicode,
EntryPoint = "MessageBoxW")]
public static extern int DisplayMessage(int hwnd, string text,
string caption, int type);
Renaming Method](https://image.slidesharecdn.com/pinvoke-140303132412-phpapp02/85/P-Invoke-Interoperability-of-C-and-C-17-320.jpg)
![using System.Runtime.InteropServices;
namespace Samples.PInvoke.IntroductionClient
{
[StructLayout(LayoutKind.Sequential)]
public class Car
{
public string Make;
public string Color;
}
// A structure containing another structure.
[StructLayout(LayoutKind.Sequential)]
public class Car2
{
public Car Car = new Car();
public string PetName;
}
}
StructLayout](https://image.slidesharecdn.com/pinvoke-140303132412-phpapp02/85/P-Invoke-Interoperability-of-C-and-C-20-320.jpg)
![// A Method returning an array of structs.
extern "C" PINVOKE_API void GiveMeThreeBasicCars(CAR** theCars)
{
auto numbOfCars = 3;
// Use CoTaskMemAlloc instead of new as .NET's P/Invoke uses
// CoTaskMemFree. See also http://blogs.msdn.com/b/dsvc/archive/2009/06/22/troubleshooting-pinvoke-related-issues.aspx
// and http://stackoverflow.com/questions/3614367/c-sharp-free-memory-allocated-by-operator-new-from-p-invoke-dll
// for details.
*theCars = (CAR*)CoTaskMemAlloc(numbOfCars * sizeof(CAR));
LPSTR carMakes[3] = { "BMW", "Ford", "Viper" };
LPSTR carColors[3] = { "Green", "Pink", "Red" };
auto pCurCar = *theCars;
for (int i = 0; i < numbOfCars; i++, pCurCar++)
{
pCurCar->color = carColors[i];
pCurCar->make = carMakes[i];
}
}
[DllImport("PInvokeIntroduction.dll", CallingConvention = CallingConvention.Cdecl, CharSet = CharSet.Ansi)]
public static extern void GiveMeThreeBasicCars(out IntPtr theCars);
public static IEnumerable<Car> GiveMeThreeBasicCarsHelper() {
const int size = 3;
var result = new List<Car>(size);
// Pass in an IntPtr as an output parameter.
IntPtr outArray;
PInvokeWrapper.GiveMeThreeBasicCars(out outArray);
try {
// Helper for iterating over array elements
IntPtr current = outArray;
for (int i = 0; i < size; i++) {
// Get next car using Marshal.PtrToStructure()
var car = Marshal.PtrToStructure<Car>(current);
result.Add(car);
// Calculate location of next structure using Marshal.SizeOf().
current = (IntPtr)((int)current + Marshal.SizeOf<Car>());
}
}
finally {
// Free memory for the allocated array.
Marshal.FreeCoTaskMem(outArray);
}
return result;
}
Marshal an Array](https://image.slidesharecdn.com/pinvoke-140303132412-phpapp02/85/P-Invoke-Interoperability-of-C-and-C-21-320.jpg)
![// extern "C" PINVOKE_API CMiniVan* CreateMiniVan();
[DllImport("PInvokeIntroduction.dll",
CallingConvention = CallingConvention.Cdecl)]
public static extern IntPtr CreateMiniVan();
// extern "C" PINVOKE_API void DeleteMiniVan(CMiniVan* obj);
[DllImport("PInvokeIntroduction.dll",
CallingConvention = CallingConvention.Cdecl)]
public static extern void DeleteMiniVan(IntPtr miniVan);
// extern "C" PINVOKE_API int GetNumberOfSeats(CMiniVan* obj);
[DllImport("PInvokeIntroduction.dll",
CallingConvention = CallingConvention.Cdecl)]
public static extern int GetNumberOfSeats(IntPtr miniVan);
var miniVan = PInvokeWrapper.CreateMiniVan();
try
{
Console.WriteLine(PInvokeWrapper.GetNumberOfSeats(miniVan));
}
finally
{
PInvokeWrapper.DeleteMiniVan(miniVan);
}
Marshalling Classes](https://image.slidesharecdn.com/pinvoke-140303132412-phpapp02/85/P-Invoke-Interoperability-of-C-and-C-23-320.jpg)
![typedef void (CALLBACK *SAYHELLOCALLBACK)();
extern "C" PINVOKE_API void CallMeBackToSayHello(
SAYHELLOCALLBACK callback);
[DllImport("PInvokeIntroduction.dll",
CallingConvention = CallingConvention.Cdecl)]
public static extern void CallMeBackToSayHello(
Action callback);
Marshalling Callbacks](https://image.slidesharecdn.com/pinvoke-140303132412-phpapp02/85/P-Invoke-Interoperability-of-C-and-C-24-320.jpg)
![typedef struct
{
double a;
double b;
double c;
} TRIANGLE;
typedef void (CALLBACK *PYTHAGORASCALLBACK)(TRIANGLE result);
extern "C" PINVOKE_API void ReportPythagorasBack(
double a, double b, PYTHAGORASCALLBACK callback);
[StructLayout(LayoutKind.Sequential)]
public struct Triangle
{
public double a;
public double b;
public double c;
}
public delegate void TriangleCallback(Triangle t);
[DllImport("PInvokeIntroduction.dll",
CallingConvention = CallingConvention.Cdecl)]
public static extern void ReportPythagorasBack(
double a, double b, TriangleCallback callback);
Marshalling Callbacks](https://image.slidesharecdn.com/pinvoke-140303132412-phpapp02/85/P-Invoke-Interoperability-of-C-and-C-25-320.jpg)
![type *identifier;
void *identifier;// Ptr to unknown type
int* pNumber;
int** ppNumber;
int*[] pArray;
// Ptr to a ptr to int
// Array of int*
int* pNumber
Console.WriteLine(*pNumber);
// Get value that pNumber points to
Pointers in C#
Supported types
sbyte, byte, short, ushort, int, uint,
long, ulong, char, float, double,
decimal, or bool.
Enums
Pointers
User-defined structs with
unmanaged types](https://image.slidesharecdn.com/pinvoke-140303132412-phpapp02/85/P-Invoke-Interoperability-of-C-and-C-28-320.jpg)
![namespace FixedSizeBuffers
{
internal unsafe struct MyBuffer
{
public fixed char fixedBuffer[128];
}
internal unsafe class MyClass
{
public MyBuffer myBuffer = default(MyBuffer);
}
internal class Program
{
static void Main()
{
MyClass myC = new MyClass();
unsafe
{
// Pin the buffer to a fixed location in memory.
fixed (char* charPtr = myC.myBuffer.fixedBuffer)
{
*charPtr = 'A';
}
}
}
}
}
Fixed size buffers
Buffer with fixed size
Typically used inside a struct
Supported data types
bool, byte, char, short, int, long,
sbyte, ushort, uint, ulong, float,
or double](https://image.slidesharecdn.com/pinvoke-140303132412-phpapp02/85/P-Invoke-Interoperability-of-C-and-C-29-320.jpg)
![Tipps & Tricks
BOOL
can be marshalled to System.Int32 or bool
Marshalling to bool is a little bit slower but convenient
See MSDN for details
InAttribute
and OutAttribute
By default, direction attribute for non-blittable types is In (performance reasons)
Best practice: Specify [In, Out] for input and output parameters (even for blittable types)
Exception: StringBuilder (In, Out by default)
See also sample in MSDN](https://image.slidesharecdn.com/pinvoke-140303132412-phpapp02/85/P-Invoke-Interoperability-of-C-and-C-31-320.jpg)
![String Marshalling
Use
[MarshalAs(UnmanagedType.ByValXXX,
SizeConst=XXX)] for fixed size char buffers
See
MSDN for details](https://image.slidesharecdn.com/pinvoke-140303132412-phpapp02/85/P-Invoke-Interoperability-of-C-and-C-34-320.jpg)
![public
{
//
//
//
static class StringIntPtrHandling
Note that GetPrivateProfileSectionNames returns a string with embedded NULL characters.
See http://msdn.microsoft.com/en-us/library/windows/desktop/ms724352(v=vs.85).aspx
for details.
[DllImport("kernel32.dll")]
static extern int GetPrivateProfileSectionNames(IntPtr lpszReturnBuffer, int nSize, string lpFileName);
public static void ExecuteSample()
{
IntPtr ptr = IntPtr.Zero;
string s = string.Empty;
try
{
// Allocate a buffer in unmanaged memory
ptr = Marshal.AllocHGlobal(1024);
// Call Kernel API
var numChars = GetPrivateProfileSectionNames(
ptr,
1024,
Path.Combine(Path.GetDirectoryName(Assembly.GetExecutingAssembly().Location), "Sample.ini"));
// Copy the buffer into a managed string
s = Marshal.PtrToStringAnsi(ptr, numChars - 1);
}
finally
{
// Free the unmanaged buffer
if (ptr != IntPtr.Zero)
{
Marshal.FreeHGlobal(ptr);
}
}
// Display the sections by splitting the string based on NULL characters
foreach (var section in s.Split('0'))
{
Console.WriteLine(section);
}
}
}
Strings and IntPtr](https://image.slidesharecdn.com/pinvoke-140303132412-phpapp02/85/P-Invoke-Interoperability-of-C-and-C-35-320.jpg)
![typedef struct
{
// Note that this structure contains an array of characters
char make[256];
char color[256];
} CARFIXED;
extern "C" PINVOKE_API void FillThreeBasicCars(CARFIXED* theCars);
[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
public struct CarStruct
{
[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 256)]
public string Make;
[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 256)]
public string Color;
}
[DllImport("PInvokeIntroduction.dll",
CallingConvention = CallingConvention.Cdecl, CharSet = CharSet.Ansi)]
public static extern void FillThreeBasicCars(
[In, Out, MarshalAs(UnmanagedType.LPArray)] CarStruct[] theCars);
Marshalling Arrays](https://image.slidesharecdn.com/pinvoke-140303132412-phpapp02/85/P-Invoke-Interoperability-of-C-and-C-36-320.jpg)
![extern "C" PINVOKE_API void GiveMeMakes(BSTR** makes, int *length);
[DllImport("PInvokeIntroduction.dll",
CallingConvention = CallingConvention.Cdecl, CharSet = CharSet.Unicode)]
public static extern void GiveMeMakes(
[Out, MarshalAs(UnmanagedType.LPArray,
ArraySubType = UnmanagedType.BStr,
SizeParamIndex = 1)] out string[] makes,
[Out] out int length);
Marshalling Arrays](https://image.slidesharecdn.com/pinvoke-140303132412-phpapp02/85/P-Invoke-Interoperability-of-C-and-C-37-320.jpg)
P/Invoke - Interoperability of C++ and C#
- 1. Training Material Rainer Stropek software architects gmbh P/Invoke Web http://www.timecockpit.com Mail [email protected] Twitter @rstropek .NET Interop Saves the day.
- 2. C++ Basics Interop-related topics for C++
- 3. // The following ifdef block is the standard way of creating macros which make exporting // from a DLL simpler. All files within this DLL are compiled with the PINVOKE_EXPORTS // symbol defined on the command line. This symbol should not be defined on any project // that uses this DLL. This way any other project whose source files include this file see // PINVOKE_EXPORTS functions as being imported from a DLL, whereas this DLL sees symbols // defined with this macro as being exported. #ifdef PINVOKE_EXPORTS #define PINVOKE_API __declspec(dllexport) #else #define PINVOKE_API __declspec(dllimport) #endif DLL Exports // Some quite simple functions to begin with extern "C" PINVOKE_API int AddNumbers(int x, int y); extern "C" PINVOKE_API int AddArray(int x[], int size); // A very simple DLL export. extern "C" PINVOKE_API int AddNumbers(int x, int y) { return x + y; } // A method taking an array. extern "C" PINVOKE_API int AddArray(int x[], int size) { auto ans = 0; for (int i = 0; i < size; i++) { ans += x[i]; } return ans; } See also MSDN
- 4. dumpbin Get list of exports of an unmanaged DLL Parameters /imports /exports See MSDN for details
- 5. Memory Handling Native DLL should avoid allocating memory and expect the caller to free the memory Use CoTaskMemAlloc instead of new Freed by Interop Marshaller of .NET automatically using CoTaskMemFree Can be freed manually using Marshal.FreeCoTaskMem Native DLL could offer a function to free the memory See CMiniVan example (CreateMiniVan and DeleteMiniVan)
- 6. Debugging Enable native code debugging Step into unmanaged code
- 8. Interop Basics System.Runtime.InteropServices Namespace System.Runtime.InteropServices.Marshal Important helper methods for working with unmanaged code class System.Runtime.InteropServices.DllImportAttribute Import a method from an unmanaged DLL
- 9. Data Type Mapping See also MSDN More detailed list can be found in Nathan, .NET and COM, 779ff Source: Troelsen, COM and .NET Interoperability
- 10. Marshal Class For details see MSDN
- 12. DllImportAttribute Calling convention Character set Entry point Exact spelling Error handling Can be used to rename functions Controls whether character set is used to look for entry point name SetLastError behavior
- 13. Calling Conventions See also MSDN article about calling conventions By default, VC++ uses _cdecl P/Invoke behavior has changed in .NET 4 In .NET < 4 you could call a _cdecl function with __stdcall without any problems In .NET >= 4 you will get an exception in the debugger See also pInvokeStackImbalance and NetFx40_PInvokeStackResilience See also http://blogs.msdn.com/b/oldnewthing/archive/2004/01/08/48616.aspx
- 14. // This works extern "C" PINVOKE_API int __stdcall AddNumbers(int x, int y); [DllImport("PInvokeIntroduction.dll")] public static extern int AddNumbers(int x, int y); // This works, too extern "C" PINVOKE_API int AddNumbers(int x, int y); [DllImport("PInvokeIntroduction.dll", CallingConvention = CallingConvention.Cdecl)] public static extern int AddNumbers(int x, int y); // Anything else will throw an exception in the debugger Calling Conventions
- 15. Marshal Strings Character sets Ansi Unicode Auto (depends on operating system type) None (obsolete) Specify character set In DllImportAttribute In MarshalAsAttribute
- 16. using System.Runtime.InteropServices; namespace Samples.PInvoke.IntroductionClient { [StructLayout(LayoutKind.Sequential)] public class Car { [MarshalAs(UnmanagedType.LPWStr)] public string Make; Character Sets [MarshalAs(UnmanagedType.LPWStr)] public string Color; } … } [DllImport("PInvokeIntroduction.dll", CallingConvention = CallingConvention.Cdecl, CharSet = CharSet.Unicode)] public static extern void DisplayBetterCar(Car2 c); See also MSDN
- 17. // Rename the MessageBoxW() function to 'DisplayMessage'. [DllImport("user32.dll", ExactSpelling = true, CharSet = CharSet.Unicode, EntryPoint = "MessageBoxW")] public static extern int DisplayMessage(int hwnd, string text, string caption, int type); Renaming Method
- 18. // Note that we pass an invalid window handle // to MessageBox error PInvokeWrapper.DisplayMessage(999, "Hello World!", "Greeting", 0); Console.WriteLine("Last Win32 Error: {0}", Marshal.GetLastWin32Error()); Console.WriteLine(new Win32Exception( Marshal.GetLastWin32Error()).Message); Win32 Errors
- 19. LayoutKind Necessary when marshalling structure Note that you can marshal structures as C# structs or classes LayoutKind.Sequential Recommendation for structure marshalling Order of the fields is preserved LayoutKind.Explicit Manually calculate the physical position of fields Combined with FieldOffsetAttribute Use FieldOffsetAttribute for implementing unions, too LayoutKind.Auto Not used for P/Invoke as C# compiler could change the order of the fields
- 20. using System.Runtime.InteropServices; namespace Samples.PInvoke.IntroductionClient { [StructLayout(LayoutKind.Sequential)] public class Car { public string Make; public string Color; } // A structure containing another structure. [StructLayout(LayoutKind.Sequential)] public class Car2 { public Car Car = new Car(); public string PetName; } } StructLayout
- 21. // A Method returning an array of structs. extern "C" PINVOKE_API void GiveMeThreeBasicCars(CAR** theCars) { auto numbOfCars = 3; // Use CoTaskMemAlloc instead of new as .NET's P/Invoke uses // CoTaskMemFree. See also http://blogs.msdn.com/b/dsvc/archive/2009/06/22/troubleshooting-pinvoke-related-issues.aspx // and http://stackoverflow.com/questions/3614367/c-sharp-free-memory-allocated-by-operator-new-from-p-invoke-dll // for details. *theCars = (CAR*)CoTaskMemAlloc(numbOfCars * sizeof(CAR)); LPSTR carMakes[3] = { "BMW", "Ford", "Viper" }; LPSTR carColors[3] = { "Green", "Pink", "Red" }; auto pCurCar = *theCars; for (int i = 0; i < numbOfCars; i++, pCurCar++) { pCurCar->color = carColors[i]; pCurCar->make = carMakes[i]; } } [DllImport("PInvokeIntroduction.dll", CallingConvention = CallingConvention.Cdecl, CharSet = CharSet.Ansi)] public static extern void GiveMeThreeBasicCars(out IntPtr theCars); public static IEnumerable<Car> GiveMeThreeBasicCarsHelper() { const int size = 3; var result = new List<Car>(size); // Pass in an IntPtr as an output parameter. IntPtr outArray; PInvokeWrapper.GiveMeThreeBasicCars(out outArray); try { // Helper for iterating over array elements IntPtr current = outArray; for (int i = 0; i < size; i++) { // Get next car using Marshal.PtrToStructure() var car = Marshal.PtrToStructure<Car>(current); result.Add(car); // Calculate location of next structure using Marshal.SizeOf(). current = (IntPtr)((int)current + Marshal.SizeOf<Car>()); } } finally { // Free memory for the allocated array. Marshal.FreeCoTaskMem(outArray); } return result; } Marshal an Array
- 22. #include "stdafx.h" // A class to be exported. class PINVOKE_API CMiniVan { private: int m_numbSeats; public: CMiniVan() { m_numbSeats = 9; } int GetNumberOfSeats() { return m_numbSeats; } }; // Functions for class extern "C" PINVOKE_API extern "C" PINVOKE_API extern "C" PINVOKE_API marshaling. CMiniVan* CreateMiniVan(); void DeleteMiniVan(CMiniVan* obj); int GetNumberOfSeats(CMiniVan* obj); Marshalling Classes
- 23. // extern "C" PINVOKE_API CMiniVan* CreateMiniVan(); [DllImport("PInvokeIntroduction.dll", CallingConvention = CallingConvention.Cdecl)] public static extern IntPtr CreateMiniVan(); // extern "C" PINVOKE_API void DeleteMiniVan(CMiniVan* obj); [DllImport("PInvokeIntroduction.dll", CallingConvention = CallingConvention.Cdecl)] public static extern void DeleteMiniVan(IntPtr miniVan); // extern "C" PINVOKE_API int GetNumberOfSeats(CMiniVan* obj); [DllImport("PInvokeIntroduction.dll", CallingConvention = CallingConvention.Cdecl)] public static extern int GetNumberOfSeats(IntPtr miniVan); var miniVan = PInvokeWrapper.CreateMiniVan(); try { Console.WriteLine(PInvokeWrapper.GetNumberOfSeats(miniVan)); } finally { PInvokeWrapper.DeleteMiniVan(miniVan); } Marshalling Classes
- 24. typedef void (CALLBACK *SAYHELLOCALLBACK)(); extern "C" PINVOKE_API void CallMeBackToSayHello( SAYHELLOCALLBACK callback); [DllImport("PInvokeIntroduction.dll", CallingConvention = CallingConvention.Cdecl)] public static extern void CallMeBackToSayHello( Action callback); Marshalling Callbacks
- 25. typedef struct { double a; double b; double c; } TRIANGLE; typedef void (CALLBACK *PYTHAGORASCALLBACK)(TRIANGLE result); extern "C" PINVOKE_API void ReportPythagorasBack( double a, double b, PYTHAGORASCALLBACK callback); [StructLayout(LayoutKind.Sequential)] public struct Triangle { public double a; public double b; public double c; } public delegate void TriangleCallback(Triangle t); [DllImport("PInvokeIntroduction.dll", CallingConvention = CallingConvention.Cdecl)] public static extern void ReportPythagorasBack( double a, double b, TriangleCallback callback); Marshalling Callbacks
- 26. Unsafe C#
- 27. Unsafe C# Use unsafe keyword Used with type or member Unsafe code block Adds pointer arithmetic to C# Similar to C# Unsafe does not mean less safe than normal C# If you use IntPtr, you are not safer In both scenarios, C# does not do any checks for buffer overruns You can program P/Invoke without unsafe Use IntPtr and methods of the Marshal class instead
- 28. type *identifier; void *identifier;// Ptr to unknown type int* pNumber; int** ppNumber; int*[] pArray; // Ptr to a ptr to int // Array of int* int* pNumber Console.WriteLine(*pNumber); // Get value that pNumber points to Pointers in C# Supported types sbyte, byte, short, ushort, int, uint, long, ulong, char, float, double, decimal, or bool. Enums Pointers User-defined structs with unmanaged types
- 29. namespace FixedSizeBuffers { internal unsafe struct MyBuffer { public fixed char fixedBuffer[128]; } internal unsafe class MyClass { public MyBuffer myBuffer = default(MyBuffer); } internal class Program { static void Main() { MyClass myC = new MyClass(); unsafe { // Pin the buffer to a fixed location in memory. fixed (char* charPtr = myC.myBuffer.fixedBuffer) { *charPtr = 'A'; } } } } } Fixed size buffers Buffer with fixed size Typically used inside a struct Supported data types bool, byte, char, short, int, long, sbyte, ushort, uint, ulong, float, or double
- 31. Tipps & Tricks BOOL can be marshalled to System.Int32 or bool Marshalling to bool is a little bit slower but convenient See MSDN for details InAttribute and OutAttribute By default, direction attribute for non-blittable types is In (performance reasons) Best practice: Specify [In, Out] for input and output parameters (even for blittable types) Exception: StringBuilder (In, Out by default) See also sample in MSDN
- 32. Memory Management Marshaler always attempts to free memory allocated by unmanaged code Use IntPtr to prevent this Memory is always freed using CoTaskMemFree Library has to provide a dedicated free method if allocated differently See MSDN for details about copying/pinning See MSDN for details
- 33. String Marshalling System.String for constant strings LPCSTR, LPCWSTR, etc. System.Text.StringBuilder for string buffers that can change LPSTR, LPWSTR, etc. Always initialize size of the StringBuilder (constructor, Capacity property) StringBuilder are guaranteed to have a terminating null character Use IntPtr and Marshal.PtrToStringXXX if caller should not free the memory
- 34. String Marshalling Use [MarshalAs(UnmanagedType.ByValXXX, SizeConst=XXX)] for fixed size char buffers See MSDN for details
- 35. public { // // // static class StringIntPtrHandling Note that GetPrivateProfileSectionNames returns a string with embedded NULL characters. See http://msdn.microsoft.com/en-us/library/windows/desktop/ms724352(v=vs.85).aspx for details. [DllImport("kernel32.dll")] static extern int GetPrivateProfileSectionNames(IntPtr lpszReturnBuffer, int nSize, string lpFileName); public static void ExecuteSample() { IntPtr ptr = IntPtr.Zero; string s = string.Empty; try { // Allocate a buffer in unmanaged memory ptr = Marshal.AllocHGlobal(1024); // Call Kernel API var numChars = GetPrivateProfileSectionNames( ptr, 1024, Path.Combine(Path.GetDirectoryName(Assembly.GetExecutingAssembly().Location), "Sample.ini")); // Copy the buffer into a managed string s = Marshal.PtrToStringAnsi(ptr, numChars - 1); } finally { // Free the unmanaged buffer if (ptr != IntPtr.Zero) { Marshal.FreeHGlobal(ptr); } } // Display the sections by splitting the string based on NULL characters foreach (var section in s.Split('0')) { Console.WriteLine(section); } } } Strings and IntPtr
- 36. typedef struct { // Note that this structure contains an array of characters char make[256]; char color[256]; } CARFIXED; extern "C" PINVOKE_API void FillThreeBasicCars(CARFIXED* theCars); [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)] public struct CarStruct { [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 256)] public string Make; [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 256)] public string Color; } [DllImport("PInvokeIntroduction.dll", CallingConvention = CallingConvention.Cdecl, CharSet = CharSet.Ansi)] public static extern void FillThreeBasicCars( [In, Out, MarshalAs(UnmanagedType.LPArray)] CarStruct[] theCars); Marshalling Arrays
- 37. extern "C" PINVOKE_API void GiveMeMakes(BSTR** makes, int *length); [DllImport("PInvokeIntroduction.dll", CallingConvention = CallingConvention.Cdecl, CharSet = CharSet.Unicode)] public static extern void GiveMeMakes( [Out, MarshalAs(UnmanagedType.LPArray, ArraySubType = UnmanagedType.BStr, SizeParamIndex = 1)] out string[] makes, [Out] out int length); Marshalling Arrays
- 38. Training Material Rainer Stropek software architects gmbh Q&A Mail [email protected] Web http://www.timecockpit.com Twitter @rstropek Thank your for coming! Saves the day.
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- 40. ist die führende Projektzeiterfassung für Knowledge Worker. Grafischer Zeitbuchungskalender, automatische Tätigkeitsaufzeichnung über Signal Tracker, umfassende Erweiterbarkeit und Anpassbarkeit, volle Offlinefähigkeit und einfachste Verwendung durch SaaS machen es zur Optimalen Lösung auch speziell im IT-Umfeld. Probieren Sie kostenlos und ohne Risiko einfach aus. Einen Testzugang erhalten Sie unter http://www.timecockpit.com. Danach nutzen Sie um nur 0,20€ pro Benutzer und Tag ohne Mindestdauer und ohne Mindestbenutzeranzahl.