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Platform Invoke Samples
This document contains the release information for the set of platform invoke samples. You will find the following sections below:
How to Use Platform Invoke Attributes
How to Marshal Structures and Unions
Building and Running the Samples
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Sample Overview
The platform invoke samples demonstrate how to call functions exported from an unmanaged library: how to declare different types, how to use available attributes to modify default behavior, how to use methods of the Marshal class when needed, and which aspects of garbage collection and threading could affect results.
Some of the samples use functions exported from Windows libraries and some use functions exported from a custom library. Here is the summary of the topics demonstrated and where are the sources located.
How to Use Platform Invoke Attributes
EntryPoint
Renames a function for use in managed code.
WinAPIs\CS\MsgBox.cs
WinAPIs\VB\MsgBox.vb
CharSet
Chooses how strings are marshaled; also affects the function name search criteria.
ExactSpelling
Indicates whether the name of the entry point in the unmanaged DLL should be modified to correspond to the CharSet value.
CallingConvention
Calls functions with varargs or calls methods of exported classes.
WinAPIs\CS\Printf.cs
WinAPIs\VB\Printf.vb
Custom\CS\ClassMethods.cs
Custom\VB\ClassMethods.vb
PreserveSig
Modifies functions that return HRESULTs.
WinAPIs\CS\CreateObject.cs
WinAPIs\VB\CreateObject.vb
SetLastError
Guarantees that the error code is saved after a function call.
WinAPIs\CS\Errors.cs
WinAPIs\VB\Errors.vb
How to Marshal Strings
string ByVal
Passes a string as an In parameter.
WinAPIs\CS\MsgBox.cs
WinAPIs\VB\MsgBox.vb
string as result
Returns a string from unmanaged code.
Custom\CS\Strings.cs
Custom\VB\Strings.vb
string ByRef
Passes a string as an In/Out parameter using StringBuilder.
WinAPIs\CS\Buffers.cs
WinAPIs\VB\Buffers.vb
string in structure ByVal
Passes a string in a structure and the structure is an In parameter.
Custom\CS\Stucts.cs
Custom\VB\Structs.vb
string in structure ByRef (char*)
Passes a string in a structure and the structure is an In/Out parameter. Unmanaged side expects a pointer to character buffer. Size of the buffer is usually passed as another member of the structure.
Custom\CS\Strings.cs
Custom\VB\Strings.vb
string in structure ByRef (char[])
Passes a string in a structure and the structure is an In/Out parameter. Unmanaged side expects embedded character buffer.
WinAPIs\CS\OSInfo.cs
WinAPIs\VB\OSInfo.vb
string in class ByVal (char*)
Passes a string in a class, which is always an In/Out parameter since it is a reference type. Unmanaged side expects a pointer to character buffer.
WinAPIs\CS\OpenFileDlg.cs
WinAPIs\VB\OpenFileDlg.vb
string in class ByVal (char[])
Passes a string in a class, which is always an In/Out parameter since it is a reference type. Unmanaged side expects embedded character buffer.
WinAPIs\CS\OSInfo.cs
WinAPIs\VB\OSInfo.vb
array of strings ByVal
Passes an array of strings ByVal.
Custom\CS\Arrays.cs
Custom\VB\Arrays.vb
array of structures that contain strings ByVal
Passes an array of structures that contain strings ByVal.
How to Marshal Structures and Unions
structure ByVal
Passes a structure as an In parameter.
Custom\CS\Stucts.cs
Custom\VB\Structs.vb
structure ByRef
Passes a structure as an In/Out parameter.
WinAPIs\CS\OSInfo.cs
WinAPIs\VB\OSInfo.vb
class ByVal
Copies a class with only integer members as an In/Out parameter like in managed case.
WinAPIs\CS\SysTime.cs
WinAPIs\VB\SysTime.vb
structure with nested structures (flattened)
Produces a class that represents a structure with nested structures on unmanaged side. Structure is flattened in one big structure on managed side.
WinAPIs\CS\FindFile.cs
WinAPIs\VB\FindFile.vb
structure with nested structures (not flattened)
Passes a structure with an embedded structure.
Custom\CS\Stucts.cs
Custom\VB\Structs.vb
structure that contains pointer to another structure
Passes a structure that contains a pointer to another structure as a member.
array of structures that contain only integers ByVal
Passes an array of structures that contain only integers as the In parameter. Members of array can be changed.
Custom\CS\Arrays.cs
Custom\VB\Arrays.vb
array of structures that contain integers and strings ByRef
Passes an array of structures that contain integers and strings as the Out parameter. Calee allocates memory for the array.
Custom\CS\OutArrayOfStructs.cs
Custom\VB\OutArrayOfStructs.vb
unions with value types
Passes a union with value types (integer and double).
Custom\CS\Unions.cs
Custom\VB\Unions.vb
unions with mixed types
Passes a union with mixed types (integer and String).
How to Marshal Arrays
array of integers ByVal
Passes an array of integers as an In parameter.
Custom\CS\Arrays.cs
Custom\VB\Arrays.vb
array of integers ByRef
Passes an array of integers as an In/Out parameter.
2D array of integers ByVal
Passing a matrix of integers as an In parameter.
Miscellaneous
HandleRef
Presents a case when HandleRef needs to be used to prevent garbage collection.
WinAPIs\CS\HandleRef.cs
WinAPIs\VB\HandleRef.vb
function pointers
Passes a delegate to an unmanaged function that expects a function pointer.
Custom\CS\Callback.cs
Custom\VB\Callback.vb
void*
Calls a function that has void* as a parameter.
Custom\CS\Void.cs
Custom\VB\Void.vb
LPARAM
Uses GCHandle to pass a managed object to unmanaged function that expects LPARAM.
WinAPIs\CS\GCHandle.cs
WinAPIs\VB\GCHandle.vb
STA/MTA
Changes the default apartment settings when an unmanaged function calls CoInitialize.
WinAPIs\CS\ActiveDir.cs
WinAPIs\VB\ActiveDir.vb
Requirements
Portions of the samples require .NET Framework and Visual C++ 6.0.
Note: The compiled DLL file is available for unmanaged portion of the sample in case you don’t have Visual Studio 6.0.
Location of the Samples
These samples are located in the Interop\pinvoke directory of the .NET Framework SDK samples directory.
For Example:
C:\Program Files\Microsoft.NET\FrameworkSDK\Samples\Technologies\Interop\pinvoke
These samples contain the following directory structure:
WinAPIs – platform invoke demonstrated with functions exported from Windows libraries
\CS – sources in C#
\VB – sources in VB.NET
Custom – platform invoke demonstrated with functions exported from custom library
\CS - sources in C#
\VB - sources in VB.NET
\LIB – custom library source
Building and Running the Samples
To run these samples, follow the instructions listed below.
1. (optional) Open the PinvokeLib.dsw file in the Custom\LIB directory with Visual Studio 6. Choose Build\Rebuild All from the menu to build library.
2. Go to the pinvoke directory and type nmake all at the prompt to build all samples.
3. Run any EXE file from a command line to see results of calls to unmanaged functions.