Exception

约 198 个字 34 行代码 预计阅读时间 1 分钟

Raise an exception

throw <<something>> // something can be any thing

Function will stop here,

clean up the stack (call destructors of all local variables),

and make its caller responsible

A good article of detailed demonstration of how exception works! click

Handle an exception

• Doesn't care

  Function will stop here,

  clean up the stack (call destructors of all local variables),

  and propagate the exception to caller

  void fun(){
    vector<int> v[5];
    v[40] = 1; -> exception
    // return to caller. The following code not touched.
    v[1] = 2;
  }
  

• Cares deeply

  try{
   // ...
  }catch(ExceptionType &e){
    // Handle the exception here
  }
  // Exception handled. The following code will be executed normally.
  cout << "Hello" << endl;
  

• Mildly interested

  try{
   // ...
  }catch(ExceptionType &e){
    // Do something
    throw; // Throw this exception again to caller.
  }
  

• Catch any type

  try{
    // ...
  }catch(...){
  
  }
  

• Selection from multiple handlers

  try{
    // ...
  }catch(Type1 &e){
  
  }catch(Type2 &e){
  
  }catch(...){
  
  }
  

  Each handler is checked one by one.

  If:

  • exact match or
  • Can apply base class conversion (pointer or ref) or
  • Catch all (...)

  The handler is matched

Exception with 'new'

• If 'new' fails, no memory is allocated

• If there is an exception after 'new', the allocated memory will not be freed.

  Solution: RAII (Resource allocation is initialization)

  Wrap the allocation inside initialization of an object.

  Because local objects' destructors will be called automatically when exception !

Exception with Ctor and Dtor

• Exception in Ctor

  Dtors will not be called automatically.

  Dynamic allocated resource will not be freed automatically.

  Solution: RAII (smart pointers)

• Exceptions in Dtor

  If Dtor is called because of exception (when clean up the stack), exceptions in Dtor will trigger std::terminate.

  Don't throw exceptions in Dtors.