使用和扩展marshal_as库

一.简介

    marshal_as库是一个托管与非托管代码间数据类型的转换模板库.

    非托管即本地 C++或C代码

二.基本用法

1.非托管到托管的字符串转换

String^ clrString; const char* pcszHello = "hello world"; clrString = marshal_as<String^>(pcszHello); wchar_t* pwszHello = L"hello wide world"; clrString = marshal_as<String^>(pwszHello); bstr_t bstrtHello("hello bstr_t world"); clrString = marshal_as<String^>(bstrtHello); std::string stdHello = "hello from std::string"; clrString = marshal_as<String^>(stdHello); CString mfcString("hello from CString"); clrString = marshal_as<String^>(mfcString); CComBSTR atrBSTR(L"hello from CComBSTR"); clrString = marshal_as<String^>(atrBST

2.托管到非非托管的字符串转换

String^ clrString = "Original System::String"; std::string stdHello = marshal_as<std::string>(clrString); CString mfcString = marshal_as<CString>(clrString); CComBSTR atrBSTR = marshal_as<CComBSTR>(clrString);

不能直接使用marshal_as转化String^类型到const char*, const wchar_t * 或者 BSTR,因为那些不受托管的资源需要在使用后被释放。为了实现这些,你需要使用一个context对象如下表所列。

marshal_context context; const char* pcszHello = context.marshal_as<const char*>(clrString); const wchar_t* pcwszHello = context.marshal_as<const wchar_t*>(clrString); BSTR bstrString = context.marshal_as<BSTR>(clrString); Console::WriteLine(context._clean_up_list.Count);

三.扩展用法

1.扩展函数, 举例:

System::Drawing::Rectangle, RECT, CRect

namespace msclr
{
    namespace interop
    {
        template<> System::Drawing::Rectangle
            marshal_as<System::Drawing::Rectangle, RECT> (
            const RECT& from)
        {
            return System::Drawing::Rectangle(from.left, from.top,
                from.right - from.left, from.bottom - from.top);
        } 
    
        template<> System::Drawing::Rectangle marshal_as<
            System::Drawing::Rectangle, CRect> (
            const CRect& from)
        {
            return System::Drawing::Rectangle(from.left, from.top,
                from.Width(), from.Height());
        } 
    
        template<> RECT marshal_as<RECT, System::Drawing::Rectangle>(
            const System::Drawing::Rectangle& from)
        {
            System::Drawing::Rectangle rectangle = from; //remove const

            RECT rect = {rectangle.Left, rectangle.Top,
                rectangle.Right, rectangle.Bottom};
            return rect;
        }
    
        template<> CRect marshal_as<CRect, System::Drawing::Rectangle>(
            const System::Drawing::Rectangle& from)
        {
            System::Drawing::Rectangle rectangle = from; //remove const

            return CRect (rectangle.Left, rectangle.Top,
                rectangle.Right, rectangle.Bottom);
        }
    }
}
 

2.扩展objects需要使用context, 举例:

namespace msclr
{
    namespace interop
    {
        template<> ref class context_node<System::Drawing::Font^, HFONT>
        : public context_node_base
        {
        private:
            System::Drawing::Font^ _font;
    
        public:
            context_node(System::Drawing::Font^% to, HFONT from)
            {
                to = _font = System::Drawing::Font::FromHfont((IntPtr)from);
            }
    
            ~context_node()
            {
                this->!context_node();
            }
    
        protected:
            !context_node()
            {
                delete _font;
            }
        };
    
        template<> ref class context_node<HFONT, System::Drawing::Font^>
        : public context_node_base
        {
        private:
            HFONT _hFont;
    
        public:
            context_node(HFONT& to, System::Drawing::Font^ from)
            {
                to = _hFont = (HFONT)from->ToHfont().ToPointer();
            }
    
            ~context_node()
            {
                this->!context_node();
            }
    
        protected:
            !context_node()
            {
                DeleteObject(_hFont);
            }
        };
    }
}