定义自己的异常：
因为从Poco::Exception继承，去定义自己的异常时，工作非常的枯燥且重复(用户需要重载大量的虚函数)，在库中提供了两个宏来完成这个工作:
POCO_DECLARE_EXCEPTION：用来申明异常宏
POCO_IMPLEMENT_EXCEPTION： 用来定义异常宏的执行体

两个宏分别定义如下：

[cpp]
// MyException.h
#include "Poco/Exception.h"
POCO_DECLARE_EXCEPTION(MyLib_API, MyException, Poco::Exception)

// MyException.h
#include "Poco/Exception.h"
POCO_DECLARE_EXCEPTION(MyLib_API, MyException, Poco::Exception)
[cpp]
// MyException.cpp
#include "MyException.h"POCO_IMPLEMENT_EXCEPTION(MyException, Poco::Exception,"Something really bad happened...")

// MyException.cpp
#include "MyException.h"POCO_IMPLEMENT_EXCEPTION(MyException, Poco::Exception,"Something really bad happened...")

宏展开分别为：
[cpp]
// MyException.h
#include "Poco/Exception.h"
POCO_DECLARE_EXCEPTION(MyLib_API, MyException, Poco::Exception)
class MyLib_API MyException: public Poco::Exception
{
public:
MyException();
MyException(const std::string& msg);
MyException(const std::string& msg, const std::string& arg);
MyException(const std::string& msg, const Poco::Exception& nested);
MyException(const MyException& exc);
~MyException();
MyException& operator = (const MyException& exc);
const char* name() const;
...
};

// MyException.h
#include "Poco/Exception.h"
POCO_DECLARE_EXCEPTION(MyLib_API, MyException, Poco::Exception)
class MyLib_API MyException: public Poco::Exception
{
public:
MyException();
MyException(const std::string& msg);
MyException(const std::string& msg, const std::string& arg);
MyException(const std::string& msg, const Poco::Exception& nested);
MyException(const MyException& exc);
~MyException();
MyException& operator = (const MyException& exc);
const char* name() const;
...
};
[cpp]
// MyException.cpp
#include "MyException.h"
POCO_IMPLEMENT_EXCEPTION(MyException, Poco::Exception,
"Something really bad happened...")
...
const char* MyException::name() const throw()
{
return "Something really bad happened...";
}
...

// MyException.cpp
#include "MyException.h"
POCO_IMPLEMENT_EXCEPTION(MyException, Poco::Exception,
"Something really bad happened...")
...
const char* MyException::name() const throw()
{
return "Something really bad happened...";
}
...

下面是一个例子：
[cpp]
#include "Poco/Exception.h"
#include
int main(int argc, char** argv)
{
Poco::Exception* pExc = 0;
try
{
throw Poco::ApplicationException("just testing");
}
catch (Poco::Exception& exc)
{
pExc = exc.clone();
}
try
{
pExc->rethrow();
}
catch (Poco::Exception& exc)
{
std::cerr << exc.displayText() << std::endl;
}
delete pExc;
return 0;
}