Question

我正试图从c＃中调用以下“foo”COM方法：

interface IFoo : public IUnknown
{
    virtual HRESULT __stdcall foo( BSTR * log ) = 0;
}

以下是我在c＃中声明的方式：

[ComImport, Guid( "98D93A58-2889-43a5-A182-47DEE781D41E" ),
 InterfaceType( ComInterfaceType.InterfaceIsIUnknown )]
public interface IFoo
{
    void foo( out string log );
}

以下是我在c＃中调用它的方式：（x是实现IFoo的COM类的实例）

string log;
x.foo( out log );

当我运行此代码时，我得到以下异常：

System.Runtime.InteropServices.MarshalDirectiveException was unhandled
  Message=Marshaler restriction: Excessively long string.

我做错了什么？

顺便说一句，如果我从c ++中调用“foo”，则以下内容正常工作：

CComBSTR log;
pX->foo( &log );

Answer 1

您应该使用ref说明符。请参阅Default Marshaling for Strings中的示例，尤其是PassStringRef1和PassStringRef2。

The following example shows strings declared in the IStringWorker interface.
Visual C++

public interface IStringWorker {
void PassString1(String s);
void PassString2([MarshalAs(UnmanagedType.BStr)]String s);
void PassString3([MarshalAs(UnmanagedType.LPStr)]String s);
void PassString4([MarshalAs(UnmanagedType.LPWStr)]String s);
void PassStringRef1(ref String s);
void PassStringRef2([MarshalAs(UnmanagedType.BStr)]ref String s);
void PassStringRef3([MarshalAs(UnmanagedType.LPStr)]ref String s);
void PassStringRef4([MarshalAs(UnmanagedType.LPWStr)]ref String s);
);

The following example shows the corresponding interface described in a type library.

[…]
interface IStringWorker : IDispatch {
HRESULT PassString1([in] BSTR s);
HRESULT PassString2([in] BSTR s);
HRESULT PassString3([in] LPStr s);
HRESULT PassString4([in] LPWStr s);
HRESULT PassStringRef1([in, out] BSTR *s);
HRESULT PassStringRef2([in, out] BSTR *s);
HRESULT PassStringRef3([in, out] LPStr *s);
HRESULT PassStringRef4([in, out] LPWStr *s);
);

如何调用从c＃获取指向BSTR的指针的COM方法

1 个答案: