Question

与this thread类似，但是当我将一个字符串传递给方法时，com类中的字符串是错误的，这里是代码：

com server - Com.idl：

interface IParamClass : IUnknown
{
    [] HRESULT SetString([in] BSTR str);
}

interface IMyClass : IUnknown
{
    [] HRESULT PassComClassAsParam([in] IParamClass* parm);
}

ParamClass.cpp

class ATL_NO_VTABLE CParamClass : ...
{
...
public:
    BSTR m_str;

    STDMETHOD(SetString)(BSTR str);
};

STDMETHODIMP CParamClass::SetString(BSTR str)
{
    m_str = str;
    return S_OK;
}

MyClass.cpp：

STDMETHODIMP CMyClass::PassComClassAsParam( IParamClass* param)
{
    CParamClass *obj = (CParamClass*)param;
    BSTR str = obj->m_str;    //debugging here, is wrong string
...
}

C＃客户端：

MyClass myobj = new MyClass();
ParamClass param = new ParamClass();
param.SetString("Test String!");
myobj.PassComClassAsParam(param);

Answer 1

您必须在此处复制字符串参数，因为您无法控制值的生命周期：

STDMETHODIMP CParamClass::SetString(BSTR str)
{
    m_str = str; // str is valid here, but you don't know when
                 // the value is destroyed later
    return S_OK;
}

当您通过m_str变量使用该值时，该字符串已被释放并销毁，因此您会看到它＆＃34;错误＆＃34;。

典型的解决方案是：

class ATL_NO_VTABLE CParamClass : ...
{
...
public:
    CComBSTR m_str; // <<--- Note CComBSTR

    STDMETHOD(SetString)(BSTR str);
};

STDMETHODIMP CParamClass::SetString(BSTR str)
{
    m_str = str;
    return S_OK;
}

如何将ATL com类对象作为参数传递给COM

1 个答案: