c - 为什么允许从 int 转换为 void *？

Question

为什么在 C 中允许从 void* 转换为 int，反之亦然？除了 pthread 之外，它还用在什么地方？

Answer 1

这是允许的，但行为是实现定义的。

有时，在某些情况下(在特定平台/体系结构上)，此规定可能对于使用运算符涉及内存地址的快速和肮脏 hacks/tricks 有用需要 int 操作数。 [例如:XOR 操作]。可用于内存有限的嵌入式设备的内存优化。

引用有关功能的标准，

The mapping functions for converting a pointer to an integer or an integer to a pointer are intended to be consistent with the addressing structure of the execution environment.

相关阅读:来自c11，第6.3.2.3章，

第 5 段:

An integer may be converted to any pointer type. Except as previously specified, the result is implementation-defined, might not be correctly aligned, might not point to an entity of the referenced type, and might be a trap representation.

和第 6 段:

Any pointer type may be converted to an integer type. Except as previously specified, the result is implementation-defined. If the result cannot be represented in the integer type, the behavior is undefined. The result need not be in the range of values of any integer type.