判断一个值是否是NaN,只能用isNaN()来判断 function f1() {} alert(f1 instanceof Function);//true alert(f1 instanceof Object);//true alert(Function instanceof Object);//true alert(Object instanceof Function);//true 32.请选择对就avascript理解有误的:〔〕 A. JScript是javascript的简称 B. java...
CObject CCmdTarget CWnd CDialog CCommonDialog CPrintDialog 要求 标头:afxdlgs.h CPrintDialog::CPrintDialog 构造Windows“打印”或“打印设置”对话框对象。 CPrintDialog( BOOL bPrintSetupOnly, DWORD dwFlags = PD_ALLPAGES | PD_USEDEVMODECOPIES | PD_NOPAGENUMS | PD_HIDEPRINTTOFILE | PD_NOSELECTION,...
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位图的图柄。 如果先前未指定位图,则返回 NULL。示例C++ 复制 CButton myBitmapButton; // Create a bitmap button. myBitmapButton.Create(_T("My button"), WS_CHILD | WS_VISIBLE | BS_BITMAP, CRect(10, 10, 60, 50), pParentWnd, 1); // If no bitmap is defined for the button, ...
翻译自:Testing if an arbitrary pointer is a valid Objective-C object 随便选一个随机指针在没有崩溃的情况下我们能否知道它是否是一个有效的Objective-C对象? 当然这没有一个简单的解决方案。在这篇文章中给出了针对64位架构的解决方案,给出的代码只在macOS 10.12.1和iOS 10.1.1中测试过。
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object-c 常用判断null的宏定义,如果是null直接返回@"" #define checkNull(__X__) (__X__) == [NSNull null] || (__X__) == nil ? @
// Check if the "thing" pass'd is empty static inline BOOL isEmpty(id thing) { return thing == nil || [thing isKindOfClass:[NSNull class]] || ([thing respondsToSelector:@selector(length)] && [(NSData *)thing length] == 0) || ([thing respondsToSelector:@selector(count)] && [(...