c – 为什么我会收到链接器错误？

/*
test.cpp
? Andrey Bushman,18 Jun 2013
*/
//--------------------------------------------
#include <exception>
#include <iostream>
using namespace std;
//--------------------------------------------
namespace Bushman{
//--------------------------------------------
    class MyClass{
    public:
        MyClass();
    };
//--------------------------------------------
    MyClass::MyClass(){
        void func(); // declaration
        func(); // call
    }
//--------------------------------------------
    void func(){ // definition
        cout << "Ping..." << endl;
    }
}
//============================================
int main()
try{
    namespace B = Bushman;
    B::MyClass a;
}
catch(exception& e){
    cerr << e.what() << endl;
    return 1;
}
catch(...){
    cerr << "Unknown exception." << endl;
    return 2;
}

结果(通过MS Visual Studio 2012)：

C:bs13>cl test.cpp /EHsc
Microsoft (R) C/C++ Optimizing Compiler
Version 17.00.51106.1 for x64 Copyright (C) Microsoft Corporation. All
rights reserved.

test.cpp
Microsoft (R) Incremental Linker Version 11.00.51106.1
Copyright (C) Microsoft Corporation. All rights reserved.

/out:test.exe test.obj test.obj : error LNK2019: unresolved external
symbol "void __cdecl func(void)" ( ?func@@YAXXZ) referenced in
function "public: __cdecl Bushman::MyClass::MyClass( void)"
(??0MyClass@Bushman@@QEAA@XZ) test.exe : fatal error LNK1120: 1
unresolved externals

C:bs13>

谢谢.