c - 为什么 sigaction 处理程序中的上下文是 void 指针？

Question

在sigaction(2)手册页中：

The siginfo_t argument to a SA_SIGINFO handler
   When the SA_SIGINFO flag is specified in act.sa_flags, the signal
   handler address is passed via the act.sa_sigaction field.  This han‐
   dler takes three arguments, as follows:

       void
       handler(int sig, siginfo_t *info, void *ucontext)
       {
           ...
       }

为什么 ucontext avoid *当手册页声明它是 a 时ucontext_t *？

ucontext
          This is a pointer to a ucontext_t structure, cast to void *.
          The structure pointed to by this field contains signal context
          information that was saved on the user-space stack by the ker‐
          nel; for details, see sigreturn(2).  Further information about
          the ucontext_t structure can be found in getcontext(3).  Com‐
          monly, the handler function doesn't make any use of the third
          argument.

Answer 1

POSIX实际上要求这是 a void *，第三个参数sigaction是：

void(*) (int, siginfo_t *, void *)

此外，由于 avoid *可以自由地转换为任何其他类型的数据指针或从任何其他类型的数据指针转换，因此在您将来可能希望无缝添加不同类型的情况下，没有理由不使用一般情况。