LNK2001 类中未解析的外部符号opengl

如何解决LNK2001 类中未解析的外部符号opengl

我试图制作一个简单的程序，可以在窗口中显示一个三角形。我还希望它在类中，而不是在主函数中。

这是我的代码：

#include <gl/glut.h>
#include <iostream>

class MainWindow {
    static MainWindow* currentInstance;

    void update() {
        glutdisplayFunc(renderCallback);
        glutKeyboardFunc(keyboardCallback);
        glutMouseFunc(mouseCallback);
    }

    //RENDER
    static void renderCallback() {
        currentInstance->render();
    }

    void render() {
        currentInstance = this;

        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

        glBegin(GL_TRIANGLES);
        glColor3f(1,0);
        glVertex2f(-0.5,-0.5);
        glColor3f(0,1,0);
        glVertex2f(0.5,1);
        glVertex2f(0.0,0.5);

        glEnd();

        glutSwapBuffers();
    }

    //KEYBOARD
    static void keyboardCallback(unsigned char c,int x,int y) {
        currentInstance->keyboard(c,x,y);
    }

    void keyboard(unsigned char c,int y) {
        if (c == 27) {
            glutDestroyWindow(glutGetwindow());
            exit(0);
        }
    }

    //MOUSE
    static void mouseCallback(int button,int state,int y) {
        currentInstance->mouse(button,state,y);
    }

    void mouse(int button,int y) {
        if (button == gluT_RIGHT_BUTTON) {
            glutDestroyWindow(glutGetwindow());
            exit(0);
        }
    }

public:
    MainWindow(int argc,char** argv) {
        glutinit(&argc,argv);
        glutinitdisplayMode(gluT_DEPTH | gluT_DOUBLE | gluT_RGBA);
        glutinitwindowPosition(100,100);
        glutinitwindowSize(640,480);
        glutCreateWindow("Simple gluT Application");

        update();

        glutMainLoop();
    }
};

int main(int argc,char** argv) {
    MainWindow window(argc,argv);
}

当我尝试编译它时出现错误：

LNK2001 unresolved external symbol "private: static class MainWindow * MainWindow::currentInstance" (?currentInstance@MainWindwo@@0PAV1@A).