关闭源代码然后再次打开后，我的 C++ 程序无法编译

Question

我编译它，它运行，然后我重新打开它，但不再工作了。这发生在 devc++ 5.8.3 和代码块中。

我的代码（注释是IDE默认的）：

    #include <windows.h>
    #include <cmath>
    #include <cstdlib>

    HPEN hPen;
    HDC hDC;
    PAINTSTRUCT Ps;

    void DrawLine(int x1, int y1, int x2, int y2, HPEN pen){
        SelectObject(hDC,pen);
        MoveToEx(hDC,x1,y1,NULL);
        LineTo(hDC,x2,y2);
    }
    void Draw(int originx, int originy, float value,int handlength){
        DrawLine(originx, originy, (handlength*cos(value*180/3.14))+originx, (handlength*sin(value*180/3.14))+originy,hPen);
        DrawLine(originx, originy, -(handlength*cos(value*180/3.14))+originx, -(handlength*sin(value*180/3.14))+originy,hPen);
    }
    /* This is where all the input to the window goes to */
    LRESULT CALLBACK WndProc(HWND hwnd, UINT Message, WPARAM wParam, LPARAM lParam) {
        switch(Message) {

            /* Upon destruction, tell the main thread to stop */
            case WM_DESTROY: {
                PostQuitMessage(0);
                break;
            }
            case WM_PAINT: {
                int r;
                int g;
                int b;
                hDC = BeginPaint(hwnd, &Ps);
                for(int i=0;i<170;i=i+1){   
                r = rand() % 256;
                g = rand() % 256;
                b = rand() % 256;
                Sleep(10);
                hPen = CreatePen(PS_INSIDEFRAME, 1, RGB(r, g, b));
                Draw(320,240,i,180);

                }       
                EndPaint(hwnd, &Ps);
                break;
            }
            /* All other messages (a lot of them) are processed using default procedures */
            default:
                return DefWindowProc(hwnd, Message, wParam, lParam);
        }
        return 0;
    }

    /* The 'main' function of Win32 GUI programs: this is where execution starts */
    int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow) {
        WNDCLASSEX wc; /* A properties struct of our window */
        HWND hwnd; /* A 'HANDLE', hence the H, or a pointer to our window */
        MSG msg; /* A temporary location for all messages */

        /* zero out the struct and set the stuff we want to modify */
        memset(&wc,0,sizeof(wc));
        wc.cbSize        = sizeof(WNDCLASSEX);
        wc.lpfnWndProc   = WndProc; /* This is where we will send messages to */
        wc.hInstance     = hInstance;
        wc.hCursor       = LoadCursor(NULL, IDC_ARROW);

        /* White, COLOR_WINDOW is just a #define for a system color, try Ctrl+Clicking it */
        wc.hbrBackground = (HBRUSH)(COLOR_WINDOW+1);
        wc.lpszClassName = "WindowClass";
        wc.hIcon         = LoadIcon(NULL, IDI_APPLICATION); /* Load a standard icon */
        wc.hIconSm       = LoadIcon(NULL, IDI_APPLICATION); /* use the name "A" to use the project icon */

        if(!RegisterClassEx(&wc)) {
            MessageBox(NULL, "Window Registration Failed!","Error!",MB_ICONEXCLAMATION|MB_OK);
            return 0;
        }

        hwnd = CreateWindowEx(WS_EX_CLIENTEDGE,"WindowClass","Lines",WS_VISIBLE|WS_OVERLAPPEDWINDOW,
            CW_USEDEFAULT, /* x */
            CW_USEDEFAULT, /* y */
            640, /* width */
            480, /* height */
            NULL,NULL,hInstance,NULL);

        if(hwnd == NULL) {
            MessageBox(NULL, "Window Creation Failed!","Error!",MB_ICONEXCLAMATION|MB_OK);
            return 0;
        }

        /*
            This is the heart of our program where all input is processed and 
            sent to WndProc. Note that GetMessage blocks code flow until it receives something, so
            this loop will not produce unreasonably high CPU usage
        */
        while(GetMessage(&msg, NULL, 0, 0) > 0) { /* If no error is received... */
            TranslateMessage(&msg); /* Translate key codes to chars if present */
            DispatchMessage(&msg); /* Send it to WndProc */
        }

        return msg.wParam;
    }

编译器日志：

C++ Compiler: C:\Program Files (x86)\Dev-Cpp\MinGW64\bin\g++.exe

Command: g++.exe "C:\Users\Pall\Desktop\proj1\lines.cpp" -o "C:\Users\Pall\Desktop\proj1\lines.exe" -g3 -I"C:\Program Files (x86)\Dev-Cpp\MinGW64\include" -I"C:\Program Files (x86)\Dev-Cpp\MinGW64\x86_64-w64-mingw32\include" -I"C:\Program Files (x86)\Dev-Cpp\MinGW64\lib\gcc\x86_64-w64-mingw32.8.1\include" -I"C:\Program Files (x86)\Dev-Cpp\MinGW64\lib\gcc\x86_64-w64-mingw32.8.1\include\c++" -L"C:\Program Files (x86)\Dev-Cpp\MinGW64\lib" -L"C:\Program Files (x86)\Dev-Cpp\MinGW64\x86_64-w64-mingw32\lib" -static-libgcc -g3 C:\Users\Pall\AppData\Local\Temp\ccRYW3Cy.o: In function DrawLine(int, int, int, int, HPEN__*)': C:/Users/Pall/Desktop/proj1/lines.cpp:12: undefined reference to__imp_SelectObject' C:/Users/Pall/Desktop/proj1/lines.cpp:13: undefined reference to __imp_MoveToEx' C:/Users/Pall/Desktop/proj1/lines.cpp:14: undefined reference to__imp_LineTo' C:\Users\Pall\AppData\Local\Temp\ccRYW3Cy.o: In function WndProc(HWND__*, unsigned int, unsigned long long, long long)': C:/Users/Pall/Desktop/proj1/lines.cpp:36: undefined reference to__imp_CreatePen' collect2.exe: error: ld returned 1 exit status

Answer 1

这是因为你需要link库libgdi32.a，如果你使用的是DevC++，点击Tools->Compiler Options，打开window，勾选框 "Add these commands to the linker command line" 并在下面的文本框中添加文本：

-lgdi32

你的表格需要这样：

关闭源代码然后再次打开后，我的 C++ 程序无法编译

My c++ programs won't compile after I close the source then open it again

c++

winapi

gcc