警告（不合时宜）：将 void(*)(int) 分配给 extern "C" void(*)(int)

我在使用 Sun 的 C++ 编译器时遇到问题。我读过甲骨文的使用函数指针 [来自 C++] http://www.oracle.com/technetwork/articles/servers-storage-dev/mixingcandcpluspluscode-305840.html#pfn。这是一本很好的书，我的印象是 SunCC 是该领域所有编译器中最合规的（尽管它给我带来了麻烦）。

测试代码如下，第24行是new_handler.sa_handler = (pfn ? pfn : &SignalHandler::NullHandler);。展开三元运算符表明这就是问题所在：new_handler.sa_handler = pfn;.

SunCC 5.11

$ /opt/solstudio12.2/bin/CC test.cxx
"test.cxx", line 24: Warning (Anachronism): Assigning void(*)(int) to extern "C" void(*)(int).
"test.cxx", line 58:     Where: While instantiating "SignalHandler<5, 0>::SignalHandler(void(*)(int), int)".
"test.cxx", line 58:     Where: Instantiated from non-template code.

SunCC 5.12

$ /opt/solarisstudio12.3/bin/CC test.cxx
"test.cxx", line 24: Warning (Anachronism): Assigning void(*)(int) to extern "C" void(*)(int).
"test.cxx", line 58:     Where: While instantiating "SignalHandler<5, 0>::SignalHandler(void(*)(int), int)".
"test.cxx", line 58:     Where: Instantiated from non-template code.

SunCC 5.13

$ /opt/solarisstudio12.4/bin/CC test.cxx
"test.cxx", line 24: Warning (Anachronism): Using void(*)(int) to initialize extern "C" void(*)(int).
"test.cxx", line 58:     Where: While instantiating "SignalHandler<5, 0>::SignalHandler(void(*)(int), int)".
"test.cxx", line 58:     Where: Instantiated from non-template code.

SunCC 5.14

$ /opt/developerstudio12.5/bin/CC test.cxx
$

我不太清楚问题是什么。 Oracle 板上有一个类似的问题，但 OP 基本上是告诉 RTFM 的：Sun Studio 11“警告（不合时宜）” https://community.oracle.com/thread/1995585.

如何解决不合时宜的警告？

solaris:~$ cat test.cxx
#include <signal.h>

extern "C" {
  typedef void (*SignalHandlerFn) (int);
};

template <int S, bool O=false>
struct SignalHandler
{
  SignalHandler(SignalHandlerFn pfn = NULL, int flags = 0) : m_installed(false)
  {
    struct sigaction new_handler;

    do
    {
      int ret = 0;

      ret = sigaction (S, 0, &m_old);
      if (ret != 0) break; // Failed

      if (m_old.sa_handler != 0 && !O) break;

      new_handler.sa_handler = (pfn ? pfn : &SignalHandler::NullHandler);
      new_handler.sa_flags = (pfn ? flags : 0);

      ret = sigemptyset (&new_handler.sa_mask);
      if (ret != 0) break; // Failed

      ret = sigaction (S, &new_handler, 0);
      if (ret != 0) break; // Failed

      m_installed = true;

    } while(0);
  }

  ~SignalHandler()
  {
    if (m_installed)
      sigaction (S, &m_old, 0);
  }

private:
  struct sigaction m_old;
  bool m_installed;

  static void NullHandler(int /*unused*/) { /* continue*/ }

private:
  // Not copyable
  SignalHandler(const SignalHandler &);
  void operator=(const SignalHandler &);
};

int main(int argc, char* argv[])
{
  SignalHandler<SIGTRAP, 0> handler;
  return 0;
}

您可以将 SignalHandler::NullHandler 更改为常规 C 函数（我们将其命名为 SignalHandler_NullHandler）。 然后将 SignalHandler_NullHandler 和 SignalHandlerFn 包装在 extern“C”中。

顺便提一句。我猜测如何“对齐”这两个函数，但您在评论中更好地解释了 C/C++ 转换存在问题。