1 STL中异常类

STL中所有内建的异常类（exception class）都继承自std::exception基类，可以分为如下三个类别：

2 获取exception的信息

2.1 what()

我们可以通过exception具体子类的what()方法获取异常的具体信息，该方法原型如下：

namespace std {
    class exception {
    public:
        virtual const char* what() const noexcept;
        ...
    };
}

2.2 code()

对于如下三种异常，可以通过code()方法获取erro_code或error_condition类型（可以通过其value用于进一步的判断，而不仅仅输出异常描述信息）。

• std::system_error：返回系统错误，对应枚举类std::errc，与errno.h中定义的系统错误码一一对应
• ios_base::failure：返回IO stream错误，对应枚举类std::io_errc
• std::future：返回多线程同步错误，对应枚举类std::future_errc

  3 异常处理模板

  ```cpp // util/exception.hpp

  include

  include

  include

  include

template void processCodeException(const T& e) { using namespace std; auto c = e.code();//获取error_code对象 cerr << “- category: “ << c.category().name() << endl; cerr << “- value: “ << c.value() << endl;//error code值 cerr << “- msg: “ << c.message() << endl;//等同与e.what() cerr << “- def category: “ << c.default_error_condition().category().name() << endl; cerr << “- def value: “ << c.default_error_condition().value() << endl; cerr << “- def msg: “ << c.default_error_condition().message() << endl; }

void processException() { using namespace std; try { throw; // rethrow exception to deal with it here } catch (const ios_base::failure& e) { cerr << “I/O EXCEPTION: “ << e.what() << endl; processCodeException(e); } catch (const system_error& e) { cerr << “SYSTEM EXCEPTION: “ << e.what() << endl; processCodeException(e); } catch (const future_error& e) { cerr << “FUTURE EXCEPTION: “ << e.what() << endl; processCodeException(e); } catch (const bad_alloc& e) { cerr << “BAD ALLOC EXCEPTION: “ << e.what() << endl; } catch (const exception& e) { cerr << “EXCEPTION: “ << e.what() << endl; } catch (…) { cerr << “EXCEPTION (unknown)” << endl; } } ```