解释 BUILD_BUG_ON(condition) ((void)sizeof(char[1 - (2 * (!(condition)))]))

这是一个编译时断言，如果条件为真，编译会通过，否则会发生编译错误。该宏的实现方式是利用了 C 语言中的数组大小必须大于 0 的特性，通过定义一个大小为 1 - (2 * (!(condition))) 的 char 数组，如果条件为真，则数组大小为 1 - 2 * 0 = 1，sizeof(char[1]) 返回 1，不产生编译错误；如果条件为假，则数组大小为 1 - 2 * 1 = -1，sizeof(char[-1]) 会产生编译错误，从而触发编译时错误。在这里，为了避免编译器警告，将数组转换成 (void) 类型进行强制类型转换。

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BUILD_BUG_ON(condition) ((void)sizeof(char[1 - (2 * (!(condition)))]))

This is a macro definition in C that is used to ensure that a particular condition is false at compile-time. If the condition is true, the macro will cause a compiler error and prevent the program from being compiled.

The macro works by creating an array of characters with a size that depends on the value of the condition. If the condition is true, the size of the array will be negative, which is not allowed in C. This will generate a compiler error.

On the other hand, if the condition is false, the size of the array will be positive, but the expression inside the sizeof operator will evaluate to 0. The macro then casts this 0 to void to avoid any warnings about unused values.

Overall, the purpose of this macro is to catch errors at compile-time rather than run-time, which can help to improve the reliability and robustness of the code.

解释 ((void)sizeof(char[1 - (2 * (!(condition)))]))

这个表达式是使用了一个条件(condition)来动态地计算char数组的大小，并将其强制转换为void类型。具体来说，当condition为真时，表达式中的!(condition)为假，因此1 - (2 * 0)等于1，所以char数组的大小为1。当condition为假时，表达式中的!(condition)为真，因此1 - (2 * 1)等于-1，所以char数组的大小为-1。由于数组大小不能为负数，所以这个表达式会编译失败。