我在使用C ++创建WIN32 GUI应用程序时遇到问题（我使用Code :: Blocks来自动生成main.cpp）。这是我为一个将对象绘制到屏幕上的类所做的头文件。
#ifndef CANVAS_H
#define CANVAS_H
#include <windows.h>
class Point{
private:
const double default_x = 0.0, default_y = 0.0;
public:
double x, y;
Point();
Point(const Point& rval);
Point(double x, double y);
bool operator==(const Point& rval);
Point& operator=(const Point& rval);
Point distanceAway(double x, double y);
};
class GraphicObject{
private:
int size;
Point offset;
Point* points;
public:
GraphicObject();
GraphicObject(const GraphicObject& rval);
void paint(HWND& hwnd, HDC hdc);
void addPoint(const Point& p);
//void removePoint(const Point& p);
};
#endif
这是实施：
#include "Canvas.h"
#include <windows.h>
//Point Class Definitions
//Default constructor
Point::Point(): x(default_x), y(default_y){}
//Copy constructor
Point::Point(const Point& rval): x(rval.x), y(rval.y){}
//Constructor
Point::Point(double x, double y): x(x), y(y){}
//Equality operator
bool Point::operator==(const Point& rval){ return (x == rval.x && y == rval.y); }
//Assignment operator
Point& Point::operator=(const Point& rval){
x = rval.x;
y = rval.y;
return *this;
}
//Function to find point certain distance away from calling object
Point Point::distanceAway(double x, double y){ return Point(this->x + x, this->y + y); }
//GraphicObject Class Definitions
//Default constructor (makes a triangle)
GraphicObject::GraphicObject(){
points = new Point[(size = 0)];
offset = Point(50,50);
}
//Copy constructor
GraphicObject::GraphicObject(const GraphicObject& rval){
delete[] points;
points = new Point[(size = rval.size)];
for(int i=0; i<size; i++){ points[i] = rval.points[i]; }
}
//Function to paint to screen
void GraphicObject::paint(HWND& hwnd, HDC hdc){
hdc = GetDC(hwnd);
for(int i=0; i<(size - 1); i++){
MoveToEx(hdc, points[i].x + offset.x, points[i].y + offset.y, NULL);
LineTo(hdc, points[i + 1].x + offset.x, points[i + 1].y + offset.y);
}
MoveToEx(hdc, points[size - 1].x + offset.x, points[size - 1].y + offset.y, NULL);
LineTo(hdc, points[0].x + offset.x, points[0].y + offset.y);
ReleaseDC(hwnd, hdc);
}
//Function to add points to shape
void GraphicObject::addPoint(const Point& p){
Point* temp = new Point[size];//DYNAMIC MEMORY temp ALLOCATED
for(int i=0; i<size; i++){
temp[i] = points[i];
}
delete[] points;
points = new Point[++size];
for(int i=0; i<(size - 1); i++){ points[i] = temp[i]; }
delete[] temp;//DYNAMIC MEMORY temp DELETED
points[size - 1] = p;
}
在main.cpp中，编译器在我实例化类GraphicObject的对象后，在该行找到错误。
#if defined(UNICODE) && !defined(_UNICODE)
#define _UNICODE
#elif defined(_UNICODE) && !defined(UNICODE)
#define UNICODE
#endif
#include <tchar.h>
#include <windows.h>
#include <iostream>
#include <chrono>
#include <thread>
#include "Canvas.h"
/* Declare Windows procedure */
LRESULT CALLBACK WindowProcedure (HWND, UINT, WPARAM, LPARAM);
/* Make the class name into a global variable */
TCHAR szClassName[ ] = _T("CodeBlocksWindowsApp");
int WINAPI WinMain (HINSTANCE hThisInstance,
HINSTANCE hPrevInstance,
LPSTR lpszArgument,
int nCmdShow)
{
HWND hwnd; /* This is the handle for our window */
MSG messages; /* Here messages to the application are saved */
WNDCLASSEX wincl; /* Data structure for the windowclass */
/* The Window structure */
wincl.hInstance = hThisInstance;
wincl.lpszClassName = szClassName;
wincl.lpfnWndProc = WindowProcedure; /* This function is called by windows */
wincl.style = CS_DBLCLKS; /* Catch double-clicks */
wincl.cbSize = sizeof (WNDCLASSEX);
/* Use default icon and mouse-pointer */
wincl.hIcon = LoadIcon (NULL, IDI_APPLICATION);
wincl.hIconSm = LoadIcon (NULL, IDI_APPLICATION);
wincl.hCursor = LoadCursor (NULL, IDC_ARROW);
wincl.lpszMenuName = NULL; /* No menu */
wincl.cbClsExtra = 0; /* No extra bytes after the window class */
wincl.cbWndExtra = 0; /* structure or the window instance */
/* Use Windows's default colour as the background of the window */
wincl.hbrBackground = (HBRUSH) COLOR_BACKGROUND;
/* Register the window class, and if it fails quit the program */
if (!RegisterClassEx (&wincl))
return 0;
/* The class is registered, let's create the program*/
hwnd = CreateWindowEx (
0, /* Extended possibilites for variation */
szClassName, /* Classname */
_T("Code::Blocks Template Windows App"), /* Title Text */
WS_OVERLAPPEDWINDOW, /* default window */
CW_USEDEFAULT, /* Windows decides the position */
CW_USEDEFAULT, /* where the window ends up on the screen */
544, /* The programs width */
375, /* and height in pixels */
HWND_DESKTOP, /* The window is a child-window to desktop */
NULL, /* No menu */
hThisInstance, /* Program Instance handler */
NULL /* No Window Creation data */
);
/* Make the window visible on the screen */
ShowWindow (hwnd, nCmdShow);
/* Run the message loop. It will run until GetMessage() returns 0 */
while (GetMessage (&messages, NULL, 0, 0))
{
/* Translate virtual-key messages into character messages */
TranslateMessage(&messages);
/* Send message to WindowProcedure */
DispatchMessage(&messages);
}
/* The program return-value is 0 - The value that PostQuitMessage() gave */
return messages.wParam;
}
int x = 0, y = 10;
GraphicObject g;
g.addPoint(Point());
/* This function is called by the Windows function DispatchMessage() */
LRESULT CALLBACK WindowProcedure (HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
PAINTSTRUCT ps;
HDC hdc;
switch (message) /* handle the messages */
{
case WM_PAINT:
//x++;
//hdc = BeginPaint(hwnd, &ps);
//hdc = GetDC(hwnd);
//Rectangle(hdc, 0, 0, 544, 375);
//TextOut(hdc, x, y, "MOVING TEXT WOO!", strlen("MOVING TEXT WOO!"));
//ReleaseDC(hwnd, hdc);
//EndPaint(hwnd, &ps);
g.paint(hwnd, hdc);
std::cout << "Window repainted\n";
Sleep(5);
break;
case WM_DESTROY:
PostQuitMessage (0); /* send a WM_QUIT to the message queue */
break;
default: /* for messages that we don't deal with */
return DefWindowProc (hwnd, message, wParam, lParam);
InvalidateRect(hwnd, NULL, true);
UpdateWindow(hwnd);
}
return 0;
}
具体来说，这条线是我遇到问题的地方：
g.addPoint(Point());
答案 0 :(得分：1)
您正在尝试使用不在命名空间范围内声明的语句。这是禁止的：声明语句以外的语句只能出现在函数体中。
要将操作应用于命名空间范围内的对象而不在函数中，即在初始化期间，您可以使用辅助对象的构造函数，例如：
GraphicObject g;
namespace {
struct g_init {
g_init() { g.addPoint(Point()); }
} init;
}
如果类型GraphicObject是可复制/可移动的，则使用函数调用初始化对象可能更容易：
namespace {
GraphicObject g_init() {
GraphicObject g;
g.addPoint(Point());
}
}
GraphicObject g = g_init();