从BSTR到字符串的转换 [英] conversion from BSTR to string

问题描述

我有一个.NET组件，它接受一个字符串对象.我有一个调用此函数的VC ++应用程序.

因此，当我将BSTR对象传递给接受字符串的.NET组件函数时，该字符串在组件内部为空.

Hi,

I have a .NET component which accepts a string object. I have a VC++ application which calls this function.

So when I pass a BSTR object to .NET component function which accepts a string, the string is empty inside the component.

How should we do this conversion i.e passing a BSTR object to .NET string object?

推荐答案

Hello，

C ++方面的示例:
接口声明

Hello,

Example from C++ side:
interface declaration

interface ISampleInterface:public IUnknown
{
    STDMETHOD(put_Value)(BSTR _value) = 0;
    STDMETHOD(get_Value)(BSTR * _value) = 0;
};

提供该功能的类示例:

Class example which provide that functionality:

class CTest : public ISampleInterface
{
	// skipped IUnknown
private:
	WCHAR m_szString[1024];
public:
	CTest() {wcscpy_s(m_szString,L"");}
public:
	STDMETHODIMP put_Value(BSTR _value);
	{
		if (!_value || !wcslen(_value)) return E_INVALIDARG;
		wcscpy_s(m_szString,_value);
		return NOERROR;
	}
        STDMETHODIMP get_Value(BSTR * _value)
	{
		if (!_value) return E_INVALIDARG;
		*_value = SysAllocString(m_szString);
		return NOERROR;
	}
};

具有指定封送处理类型的C#端示例:
这是指定的类型，因此.NET将在RCW中进行封送处理.

Example on C# side with specify marshaling type:
Here is type specified so .NET will do marshaling stuff in RCW.

[InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
public interface ISampleInterface
{
    [PreserveSig]
    int put_Value([In, MarshalAs(UnmanagedType.BStr)] string _value);

    [PreserveSig]
    int get_Value([Out, MarshalAs(UnmanagedType.BStr)] out string _value);
}

没有封送处理的C#端示例:
在这里，您可以直接执行封送处理类型.

Example on C# side without marshaling:
Here you directly perform marshaling type.

[InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
public interface ISampleInterface
{
    [PreserveSig]
    int put_Value(IntPtr _value);

    [PreserveSig]
    int get_Value(out IntPtr _value);
}

对于此类声明，您应该具有以下代码:

For such declaration you should have code:

// initialized somewhere
ISampleInterface _sample;
// Put value
{
    IntPtr _ptr = Marshal.StringToBSTR("some string");
    _sample.put_Value(_ptr);
    Marshal.FreeBSTR(_ptr);
}
// Get value
{
    IntPtr _ptr;
    _sample.get_Value(out _ptr);
    string _result = Marshal.PtrToStringBSTR(_ptr);
    Marshal.FreeBSTR(_ptr);
}

问候，
Maxim.

Regards,
Maxim.

您好！我假设您的组件中有put_StringData(BSTR str)，因此对于std :: string，您可以使用以下代码:

Hello! I presume, that you have put_StringData(BSTR str ) in your component, so for std::string you could use this code:

std::string std_string = "Some string data";
_bstr_t some_string = std_string.c_str();

mycomponent->put_StringData(some_string.GetBSTR());

或用于CString te following

or for CString te following

CString cstr_string = "Some string data";
_bstr_t some_string(cstr_string);

mycomponent->put_StringData(some_string.GetBSTR());

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