可以手动抛出std :: bad_alloc吗？

Question

我有这个代码..

 CEngineLayer::CEngineLayer(void)
 {
    // Incoming creation of layers. Wrapping all of this in a try/catch block is
    // not helpful if logging of errors will happen.

    logger = new (std::nothrow) CLogger(this);

    if(logger == 0)
    {
     std::bad_alloc exception;
     throw exception;
    }

    videoLayer = new (std::nothrow) CVideoLayer(this);

    if(videoLayer == 0)
    {
     logger->log("Unable to create the video layer!");

     std::bad_alloc exception;
     throw exception;
    }
 }

 IEngineLayer* createEngineLayer(void)
 {
    // Using std::nothrow would be a bad idea here as catching things thrown
    // from the constructor is needed.

    try
    {
     CEngineLayer* newLayer = new CEngineLayer;

     return (IEngineLayer*)newLayer;
    }
    catch(std::bad_alloc& exception)
    {
     // Couldn't allocate enough memory for the engine layer.
     return 0;
    }
 }

我省略了大部分不相关的信息,但我认为这里的图片很清楚.

是否可以手动抛出std :: bad_alloc而不是单独尝试/捕获所有图层创建并在重新抛出bad_allocs之前进行记录？

Answer 1

只是回答这个问题(因为似乎没有其他人回答过它),C++ 03标准定义std::bad_alloc如下:

namespace std {
  class bad_alloc : public exception {
  public:
    bad_alloc() throw();
    bad_alloc(const bad_alloc&) throw();
    bad_alloc& operator=(const bad_alloc&) throw();
    virtual ˜bad_alloc() throw();
    virtual const char* what() const throw();
  };
}

由于标准定义了一个公共构造函数,因此构造并从代码中抛出一个是非常安全的.(可以抛出具有公共拷贝构造函数的任何对象,IIRC).

Answer 2

你不需要这样做.您可以使用throw语句的无参数形式来捕获std::bad_alloc异常,记录它,然后重新抛出它:

logger = new CLogger(this);
try {
    videoLayer = new CVideoLayer(this);
} catch (std::bad_alloc&) {
    logger->log("Not enough memory to create the video layer.");
    throw;
}

或者,如果logger不是智能指针(它应该是):

logger = new CLogger(this);
try {
    videoLayer = new CVideoLayer(this);
} catch (std::bad_alloc&) {
    logger->log("Not enough memory to create the video layer.");
    delete logger;
    throw;
} catch (...) {
    delete logger;
    throw;
}

Answer 3

如果我在STL容器中使用一些自定义分配器,我个人会抛弃它.我们的想法是将相同的接口(包括行为方面)作为默认的std :: allocator呈现给STL库.

因此,如果您有自定义分配器(例如,从内存池分配一个)并且底层分配失败,请调用"throw std :: bad_alloc".这保证了调用者,其中99.9999%的时间是某个STL容器,将正确地对其进行调整.如果分配器返回一个大的胖0,你无法控制那些STL实现会做什么 - 它不太可能是你想要的任何东西.