C + + Exception 2

include <iostream>                                                                using namespace std;class  a{};class b:public a{};void func (void) {    //throw b (); Can throw A also can throw B    throw a ();} Int main (void) {    try{        func ();     }       catch (B& ex) {         cout <<  "Catch:b"  << endl;//if catch  here (a&  ex) and catch (B& ex)                                    //interchange, the result is catch:a        return -1;      }       catch (A& ex) {         cout <<  "Catch:a"  << endl;         return -1;     }        return 0; }

The catch clause matches top-down order based on the type of the exception, not the optimal match

Use references in catch clauses to accept exception objects, avoid the performance overhead of copy constructs, and reduce the risk of shallow copies

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C + + Exception 2