在C++/CLI环境下，千万不要把普通全局函数当标准C/C++的函数指针传递给native的库使用

先上一个简单代码：

#include <cstdlib>
#include <cstdio>

// native apis
extern "C"
{
    typedef void (*CallbackFunction)(int value);

    CallbackFunction GlobalFunction;
    __declspec(dllexport) void NativeSetCallback(CallbackFunction func)
    {
        GlobalFunction = func;
    }
}

// test cli
namespace Project2
{
    static void CliGlobalCallback(int value)
    {
        System::Console::WriteLine(System::String::Format("{0}", value));
    }

    extern "C"
    {
        static void StandardGlobalCallback(int value)
        {
            printf_s("%d", value);
        }
    }
}

extern "C"
{
    // 这样才可以防止前面的Callback被strip
    __declspec(dllexport) void NativeTestAPI()
    {
        NativeSetCallback(Project2::CliGlobalCallback);
        NativeSetCallback(Project2::StandardGlobalCallback);
    }
}

从直观感觉上来看，CliGlobalCallback和StandardGlobalCallback的函数签名是一样的，都传递给NativeSetCallback也不会报错，然而实际上这两个函数的签名并不相同。查看生成的二进制代码可以看到如下区别：

.nep: ; =============== S U B R O U T I N E =======================================
.nep:
.nep:
.nep: ; void __fastcall Project2::`anonymous namespace'::CliGlobalCallback(Project2::_anonymous_namespace_ *__hidden this, int)
.nep: ?CliGlobalCallback@?A0x1736b8ca@Project2@@YAXH@Z proc near
.nep:                                         ; DATA XREF: .rdata:__unep@?CliGlobalCallback@?A0x1736b8ca@Project2@@$$FYAXH@Z↓o
.nep:                 jmp     short loc_18000502A
.nep: ; ---------------------------------------------------------------------------
.nep:                 ud2
.nep: ; ---------------------------------------------------------------------------
.nep:                 jmp     cs:__m2mep@?CliGlobalCallback@?A0x1736b8ca@Project2@@$$FYAXH@Z
.nep:000000018000502A ; ---------------------------------------------------------------------------
.nep:000000018000502A
.nep:000000018000502A loc_18000502A:                          ; CODE XREF: Project2::`anonymous namespace'::CliGlobalCallback(int)↑j
.nep:000000018000502A                 jmp     cs:__mep@?CliGlobalCallback@?A0x1736b8ca@Project2@@$$FYAXH@Z
.nep:000000018000502A ?CliGlobalCallback@?A0x1736b8ca@Project2@@YAXH@Z endp
.nep:000000018000502A
.nep:
.nep: ; =============== S U B R O U T I N E =======================================
.nep:
.nep:
.nep: StandardGlobalCallback@0x1736b8ca proc near
.nep:                                         ; DATA XREF: .rdata:__unep@?StandardGlobalCallback@?A0x1736b8ca@@$$J0YAXH@Z↓o
.nep:                 jmp     short loc_18000503A
.nep: ; ---------------------------------------------------------------------------
.nep:                 ud2
.nep: ; ---------------------------------------------------------------------------
.nep:                 jmp     cs:__m2mep@?StandardGlobalCallback@?A0x1736b8ca@@$$J0YAXH@Z
.nep:000000018000503A ; ---------------------------------------------------------------------------
.nep:000000018000503A
.nep:000000018000503A loc_18000503A:                          ; CODE XREF: StandardGlobalCallback@0x1736b8ca↑j
.nep:000000018000503A                 jmp     cs:__mep@?StandardGlobalCallback@?A0x1736b8ca@@$$J0YAXH@Z
.nep:000000018000503A StandardGlobalCallback@0x1736b8ca endp
.nep:000000018000503A

CLI版本函数签名中，有一个隐藏的__this，这在调用时，应该是需要有参数来提供的，虽然不是用户手动提供。因此如果将CLI的这个函数作为普通的函数指针传递给Native的函数并作为普通的Native函数指针使用会导致CLI堆损坏，导致极其难查的崩溃，因为崩溃现场跟这里八竿子打不到一块儿去了。

正确的做法是使用extern "C"把它包起来，无论你在函数内部是否访问CLI的代码，都没关系。比如这样：

// test cli
namespace Project2
{
    extern "C"
    {
        static void CliGlobalCallback(int value)
        {
            System::Console::WriteLine(System::String::Format("{0}", value));
        }
    }

    extern "C"
    {
        static void StandardGlobalCallback(int value)
        {
            printf_s("%d", value);
        }
    }
}

然后再看一下汇编：

.nep: ; =============== S U B R O U T I N E =======================================
.nep:
.nep:
.nep: CliGlobalCallback@0x1736b8ca proc near  ; DATA XREF: .rdata:__unep@?CliGlobalCallback@?A0x1736b8ca@@$$J0YAXH@Z↓o
.nep:                 jmp     short loc_18000502A
.nep: ; ---------------------------------------------------------------------------
.nep:                 ud2
.nep: ; ---------------------------------------------------------------------------
.nep:                 jmp     cs:__m2mep@?CliGlobalCallback@?A0x1736b8ca@@$$J0YAXH@Z
.nep:000000018000502A ; ---------------------------------------------------------------------------
.nep:000000018000502A
.nep:000000018000502A loc_18000502A:                          ; CODE XREF: CliGlobalCallback@0x1736b8ca↑j
.nep:000000018000502A                 jmp     cs:__mep@?CliGlobalCallback@?A0x1736b8ca@@$$J0YAXH@Z
.nep:000000018000502A CliGlobalCallback@0x1736b8ca endp
.nep:000000018000502A
.nep:
.nep: ; =============== S U B R O U T I N E =======================================
.nep:
.nep:
.nep: StandardGlobalCallback@0x1736b8ca proc near
.nep:                                         ; DATA XREF: .rdata:__unep@?StandardGlobalCallback@?A0x1736b8ca@@$$J0YAXH@Z↓o
.nep:                 jmp     short loc_18000503A
.nep: ; ---------------------------------------------------------------------------
.nep:                 ud2
.nep: ; ---------------------------------------------------------------------------
.nep:                 jmp     cs:__m2mep@?StandardGlobalCallback@?A0x1736b8ca@@$$J0YAXH@Z
.nep:000000018000503A ; ---------------------------------------------------------------------------
.nep:000000018000503A
.nep:000000018000503A loc_18000503A:                          ; CODE XREF: StandardGlobalCallback@0x1736b8ca↑j
.nep:000000018000503A                 jmp     cs:__mep@?StandardGlobalCallback@?A0x1736b8ca@@$$J0YAXH@Z
.nep:000000018000503A StandardGlobalCallback@0x1736b8ca endp
.nep:000000018000503A
.nep:
.nep: ; =============== S U B R O U T I N E =======================================
.nep:
.nep:

这样再传递给Native就稳了。