在C/C ++中定义类型化的常数 [英] defining typed constant numbers in C/C++

问题描述

在C/C ++中，说(1U)与((unsigned int)1)之间有区别吗?我更喜欢第二个，但是我担心第二个可能在运行时进行类型转换(即额外的cpu周期)，而第一个在编译时会得到正确的类型.谢谢.

In C/C++, is there a difference between saying (1U) vs. ((unsigned int)1) ? I prefer the second one, but I am concerned that the second one may be type-cast at run time (i.e. extra cpu cycles), whereas the first one gets the correct type at compilation. Thanks.

推荐答案

它们不是等效的. 1U在#if预处理指令中有效. (unsigned int)1是预处理器级别的语法错误.但是，您可以将其设置为(unsigned)+1，并且在预处理器中将是有效的，但是仅由于一条晦涩的规则，很少有人知道.

They're not equivalent. 1U is valid in #if preprocessing directives. (unsigned int)1 is a syntax error at the preprocessor level. You could however make it (unsigned)+1 and it would be valid in the preprocessor, but only because of an obscure rule few people know..

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