C 中的 typeof 运算符 [英] typeof operator in C

问题描述

C 中的 typeof 真的是一个运算符吗?
我在想，因为 C 中没有多态性，所以在运行时没有什么可做的.也就是说，typeof 的答案在编译时是已知的.(我想不出在编译时不会知道 typeof 的用法.)所以它看起来更像是一个编译时指令，而不是一个运算符.

Is typeof in C, really an operator?
I'm thinking because there is no polymorphism in C, that there is nothing to do at run-time. That is, the answer to typeof is known at compile-time. (I can't think of a use of typeof that would not be known at compile time.) So it appears to be more of a compile-time directive, than an operator.

typeof 是否使用任何(处理器)运行时(在 GCC 中)?

Does typeof use any (processor) run-time (in GCC)?

推荐答案

由于 typeof 是一个编译器扩展，所以并没有真正的定义，但在 C 的传统中它会是一个运算符，例如 sizeof 和 _Alignof 也被视为运算符.

Since typeof is a compiler extension, there is not really a definition for it, but in the tradition of C it would be an operator, e.g sizeof and _Alignof are also seen as an operators.

您弄错了，C 具有仅在运行时确定的动态类型:变量修改 (VM) 类型.

And you are mistaken, C has dynamic types that are only determined at run time: variable modified (VM) types.

size_t n = strtoull(argv[1], 0, 0);
double A[n][n];
typeof(A) B;

只能在运行时确定.

在 2021 年添加:typeof 与 sizeof 规则相似的很有可能会进入 C23.

Add on in 2021: there are good chances that typeof with similar rules as for sizeof will make it into C23.

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