Methods defined in native code can be invoked using the platform invoke (also know as PInvoke or p/invoke) functionality of the CLI. Platform invoke will switch from managed to unmanaged state and back, and also handle necessary data marshalling. Methods that need to be called using PInvoke are marked as pinvokeimpl. In addition, the methods shall have the implementation attributes native and unmanaged (§II.15.4.2.4).
| MethAttr ::= | Description | Clause |
|---|---|---|
pinvokeimpl '(' QSTRING [ as QSTRING ] PinvAttr* ')' |
Implemented in native code | |
| | … | §II.15.4.1.5 |
The first quoted string is a platform-specific description indicating where the implementation of the method is located (for example, on Microsoft Windows™ this would be the name of the DLL that implements the method). The second (optional) string is the name of the method as it exists on that platform, since the platform can use name-mangling rules that force the name as it appears to a managed program to differ from the name as seen in the native implementation (this is common, for example, when the native code is generated by a C++ compiler).
Only static methods, defined at global scope (i.e., outside of any type), can be marked pinvokeimpl. A method declared with pinvokeimpl shall not have a body specified as part of the definition.
| PinvAttr ::= | Description (platform-specific, suggestion only) |
|---|---|
ansi |
ANSI character set. |
| autochar |
Determine character set automatically. |
| cdecl |
Standard C style call |
| fastcall |
C style fastcall. |
| stdcall |
Standard C++ style call. |
| thiscall |
The method accepts an implicit this pointer. |
| unicode |
Unicode character set. |
| platformapi |
Use call convention appropriate to target platform. |
The attributes ansi, autochar, and unicode are mutually exclusive. They govern how strings will be marshaled for calls to this method: ansi indicates that the native code will receive (and possibly return) a platform-specific representation that corresponds to a string encoded in the ANSI character set (typically this would match the representation of a C or C++ string constant); autochar indicates a platform-specific representation that is "natural" for the underlying platform; and unicode indicates a platform-specific representation that corresponds to a string encoded for use with Unicode methods on that platform.
The attributes cdecl, fastcall, stdcall, thiscall, and platformapi are mutually exclusive. They are platform-specific and specify the calling conventions for native code.
[Example: The following shows the declaration of the method MessageBeep located in the Microsoft Windows™ DLL user32.dll:
.method public static pinvokeimpl("user32.dll" stdcall) int8
MessageBeep(unsigned int32) native unmanaged {}
end example]