我的第一个 DLL 有很多编译错误我不明白

Question

我正在尝试创建我的第一个简单 DLL。 I have a class(that's a singleton class) & a Window Procedure function that I declare in the DLL & want to import in my project later on. My IDE is Microsoft Visual C++ 2010 & my project is a Win32 DLL one & I have used MSVC++ default DLL template(you know how it creates all the default files when I create the project).

但是我收到了这些编译错误，我不明白出了什么问题？

1>c:\users\soribo\dropbox\c++ 编程\visual c++ 编程\testcreatedll\testcreatedll\dlltest.h(15): 错误 C2059: 语法错误: '__declspec(dllimport)'
1>c:\users\soribo\dropbox\c++ 编程\visual c++ 编程\testcreatedll\testcreatedll\dlltest.h(39): 错误 C2065: 'TestWndProc': 未声明的标识符
1>c:\users\soribo\dropbox\c++ 编程\visual c++ 编程\testcreatedll\testcreatedll\dlltest.cpp(7): 警告 C4273: 'testStaticVar': dll 链接不一致
1> c:\users\soribo\dropbox\c++ programming\visual c++ programming\testcreatedll\testcreatedll\dlltest.h(21): see previous definition of 'public: static bool MyTest::TestClass::testStaticVar'
1>c:\users\soribo\dropbox\c++ 编程\visual c++ 编程\testcreatedll\testcreatedll\dlltest.cpp(7): 错误 C2491: 'MyTest::TestClass::testStaticVar': 定义 dllimport ZA81259CEF8E959C624DF1D456E5D39 不允许成员数据
1>c:\users\soribo\dropbox\c++ 编程\visual c++ 编程\testcreatedll\testcreatedll\dlltest.cpp(8): 警告 C4273: 'instance': 不一致的 dll 链接
1> c:\users\soribo\dropbox\c++ programming\visual c++ programming\testcreatedll\testcreatedll\dlltest.h(35): see previous definition of 'private: static MyTest::TestClass * MyTest::TestClass::instance'
1>c:\users\soribo\dropbox\c++ 编程\visual c++ 编程\testcreatedll\testcreatedll\dlltest.cpp(8): 错误 C2491: 'MyTest::TestClass::instance': 定义 dllimport static 数据成员不允许

我的简单 header 文件：

#ifndef DLLTEST_H
#define DLLTEST_H

#include <windows.h>

// This is from a tutorial I am following
#ifdef _CLASSINDLL
#define CLASSINDLL_CLASS_DECL __declspec(dllexport)
#else
#define CLASSINDLL_CLASS_DECL __declspec(dllimport)
#endif

namespace MyTest
{
    LRESULT CALLBACK CLASSINDLL_CLASS_DECL TestWndProc( HWND hwnd, UINT msg, LPARAM lParam, WPARAM wParam );

    class CLASSINDLL_CLASS_DECL TestClass
    {
        // Singleton class
        public:
            static bool testStaticVar;

            static TestClass* getInstance()
            {
                if ( instance == NULL ) { instance = new TestClass(); }
                return instance;
            }

            void add()
            {
                myMember++;
            }

        private:
            static TestClass* instance;
            WNDPROC myProc;
            int myMember;

            TestClass() : myMember(0) { myProc = (WNDPROC)&TestWndProc; }
            ~TestClass()              {}

    };
}

#endif // DLLTEST_H

我的简单cpp文件：

#include "stdafx.h"
#include "DLLTest.h"

namespace MyTest
{
    // Create/Initialise? Class Static variables
    bool TestClass::testStaticVar = false;
    TestClass* TestClass::instance = NULL;

    LRESULT CALLBACK TestWndProc( HWND hwnd, UINT msg, LPARAM lParam, WPARAM wParam )
    {
        switch (msg)
        {
            case WM_CREATE:
            {

            }
            break;
            default:
            break;
        }

        return DefWindowProc(hwnd, msg, wParam, lParam);
    }

}

Answer 1

我认为您缺少 _CLASSINDLL 预处理器定义。 将其添加到项目 -> 属性 -> C/C++ -> 预处理器 -> 预处理器定义中。