切记:如果decltype ((variable))双层括号的结果永远是引用,而decltype(variable)的结果只有 variable 是引用时才是引用。 赋值是会产生引用的一类典型表达式,引用的类型就是左值的类型。也就是说,如果 i 是 int 类型,则表达式 i = x的类型是 int& 。 示例 inta =3, b =4;decltype(a) c = a;// c 是 ...
本文尝试从gcc的关键字typeof和宏offsetof入手,循序渐进地剖析宏container_of之实现原理。 1. typeof(from:https://en.wikipedia.org/wiki/Typeof) typeof is an operator provided by several programming languages to determine the data type of a variable. This is useful when constructing programs that mus...
structline*thisline=malloc(sizeof(structline) +this_length); thisline->length = this_length; 如上例所示, struct line 数据结构定义了一个int length变量和一个变长数组contents[0],这个struct line数据结构的大小只包含int类型的大小,不包含contents的大小,也就是**sizeof (struct line) = sizeof (int...
New in the C23 standard, the typeof operator is a unary operator that returns the type of an expression. It can be used in type declarations, type casts, type checks, and so on. It gets the type of a variable, function, or any C expression. The __typeof__ keyword is a Microsoft...
拓展: typeof通常被用在复杂宏的语句表达式中,下面的例子,用来说明如何使用typeof来获取宏参数的类型,并且安全地让宏参数只运行一遍: ?...更多关于typeof的例子: 1,定义一个变量,类型跟x指向的数据相同 typeof (*x) y; 2,定义一个数组,元素的类型跟x指向的数据相
Thetypeofoperator returns the type of a variable or an expression. Examples typeof"John"// Returns string typeof("John"+"Doe")// Returns string typeof3.14// Returns number typeof33// Returns number typeof(33+66)// Returns number
valuebaseTypevaluebaseTypebaseTypetagvalueSymboltoStringTagtagtagbaseTypeprototypevalue// 构造函数的名称;例如 `Array`、`GeneratorFunction`、`Number`、`String`、`Boolean` 或 `MyCustomClass`constclassName=value.constructor.name;if(typeofclassName==="string"&&className!==""){returnclassName;}// 在这一...
New in the C23 standard, thetypeofoperator is a unary operator that returns the type of an expression. It can be used in type declarations, type casts, type checks, and so on. It gets the type of a variable, function, or any C expression. ...
If you try to perform those same operations on a variable of type bool, the compiler generates an error, as shown in the following example: C# Copy int a = 5; int b = a + 2; //OK bool test = true; // Error. Operator '+' cannot be applied to operands of type 'int' and ...
JavaScript 中 typeof 实现原理 介绍 Try it typeof操作符返回一个字符串,表示未经计算的操作数的类型。 typeof42;// "number"typeof'cellinlab';// "string"typeoftrue;// "boolean"typeofundeclaredVariable;// "undefined" 描述 typeof可能的返回值。