C++获取屏幕分辨率（屏幕窗口大小），屏幕显示比例（DPI）几种方法

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1. 获取屏幕的分辨率的几种方法

   #include <Windows.h>
   
   #include <iostream>
   int main(void) {
   	HWND hd = GetDesktopWindow();
   	// 方法一
   	RECT rect;
   	// 只获得窗口客户区的大小
   	GetClientRect(hd, &rect);
   	int client_width = (rect.right - rect.left);
   	int client_height = (rect.bottom - rect.top);
   	std::cout << "client width:" << client_width << std::endl;
   	std::cout << "client height:" << client_height << std::endl;
   	// 获取到的是窗口在屏幕上的位置
   	GetWindowRect(hd, &rect);
   	int window_width = (rect.right - rect.left);
   	int window_height = (rect.bottom - rect.top);
   	std::cout << "window width:" << window_width << std::endl;
   	std::cout << "window height:" << window_height << std::endl;
   
   	// 方法二
   	// 不带菜单栏的大小
   	int no_menu_bar_width = GetSystemMetrics(SM_CXFULLSCREEN);
   	int no_menu_bar__height = GetSystemMetrics(SM_CYFULLSCREEN);
   	std::cout << "no menu bar width:" << no_menu_bar_width << std::endl;
   	std::cout << "no menu bar height:" << no_menu_bar__height << std::endl;
   	// 带标题栏和菜单栏
   	int have_menu_bar_width = GetSystemMetrics(SM_CXSCREEN);
   	int have_menu_bar_height = GetSystemMetrics(SM_CYSCREEN);
   	std::cout << "have menu bar width:" << window_width << std::endl;
   	std::cout << "have menu bar height:" << window_height << std::endl;
   
   	//方法三
   	HDC hdc = GetDC(NULL);                           // 得到屏幕DC  
   	client_width = GetDeviceCaps(hdc, HORZRES);      // 宽  
   	client_height = GetDeviceCaps(hdc, VERTRES);     // 高   
   	ReleaseDC(NULL, hdc);                            // 释放DC
   	std::cout << "client width:" << client_width << std::endl;
   	std::cout << "client height:" << client_height << std::endl;
   
   	//方法四
   	SystemParametersInfo(SPI_GETWORKAREA, 0, &rect, SPIF_SENDCHANGE);
   	client_width = (rect.right - rect.left);
   	client_height = (rect.bottom - rect.top);
   	std::cout << "client width:" << client_width << std::endl;
   	std::cout << "client height:" << client_height << std::endl;
   
   	//方法五
   	hdc = GetDC(NULL);
   	client_width = GetDeviceCaps(hdc, DESKTOPHORZRES);
   	client_height = GetDeviceCaps(hdc, DESKTOPVERTRES);
   	ReleaseDC(NULL, hdc);
   	std::cout << "client width:" << client_width << std::endl;
   	std::cout << "client height:" << client_height << std::endl;
   
   	getchar();
   	return 0;
   }

2. 获取屏幕显示比例

   #include <iostream>
   #include <Windows.h>
   
   int main(void) {
   	HWND hd = GetDesktopWindow();
   	int zoom = GetDpiForWindow(hd);
   	double dpi = 0;
   	switch (zoom) {
   	case 96:
   		dpi = 1;
   		std::cout << "100%" << std::endl;
   		break;
   	case 120:
   		dpi = 1.25;
   		std::cout << "125%" << std::endl;
   		break;
   	case 144:
   		dpi = 1.5;
   		std::cout << "150%" << std::endl;
   		break;
   	case 192:
   		dpi = 2;
   		std::cout << "200%" << std::endl;
   		break;
   	default:
   		std::cout << "error" << std::endl;
   		break;
   	}
   	getchar();
   	return 0;
   }

3. 在获取屏幕显示比例的时候，我们可以发现方法一到方法四都是获取的是缩放后的屏幕分辨率，要想获得最初的屏幕我们需要乘以对应的dpi就可以了。

   int client_width = (rect.right - rect.left) * dpi;
   int client_height = (rect.bottom - rect.top) * dpi;