“ static_cast< void>”的用法是什么？在宏？ [英] what is the use of "static_cast<void>" in macro?

问题描述

我看到了这样的宏定义：

I'm seeing a macro definition like this:

#define ASSERT_VALID_PARAM(param, assertion) {  static_cast<void>(param); if (!(assertion)) { throw InvalidParamError(#param, #assertion, __FILE__, __PRETTY_FUNCTION__, __LINE__); } }

我不知道是否需要 static_cast< void>（参数）在这里。
关于为什么需要这样做的任何想法？

I'm not able to figure out the need of static_cast<void>(param) here. Any idea on why this is needed?

推荐答案

此宏旨在验证某个 real 参数传递特定的验证规则。宏的逻辑部分由两部分组成：

This macro is designed to validate a certain real parameter passes a certain validation rule(s). The logic part of the macro is composed of 2 parts:

1. 验证 param 是具有有效名称的实参。这是通过使用 static_cast 完成的，如果使用了非法名称，则会生成编译时错误。


2. 验证断言的真实性。

1. Validate that param is a real parameter, with a valid name. This is done by using the static_cast, and if an illegal name is used, a compile time error will be generated.
2. Validate the "truthyness" of assertion. This is done with a simple negating if statement.

如果参数是有效名称，并且断言失败（ assertion == false ），使用传入的参数作为字符串（使用 InvalidParamError //msdn.microsoft.com/zh-cn/library/7e3a913x.aspx rel = nofollow> 字符串化运算符＃ ）来初始化错误对象。

If the param is a valid name, and the assertion fails (assertion == false), an InvalidParamError is thrown, using the passed in parameters as strings (using the Stringizing operator #) to initialize the error object.

由于宏中 param 参数的实际用法仅是字符串，因此必须使用实际代码进行验证。由于不需要实际操作，因此使用static_cast，它会丢弃结果，并且有可能进行优化。如果没有该检查，则可以传递任何值，该值将使断言中的信息毫无意义。

Since the actual usage of the param parameter in the macro is only as a string, it has to be validated using actual code. Since no real operation is needed the static_cast is used, which discards the result and can potentially be optimized out. Without that check, you could pass any value which would make the information in the assertion meaningless.

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