catch异常的常见误区

时间：2011-03-13 来源：studycpp

1，异常对象总是在抛出点创建。

 1 //myException1.cpp
 2  #include<iostream>
 3  using namespace std;
 4 
 5  class myException
 6 {
 7  public:
 8     myException()
 9     {
10         cout<<"default construct"<<endl;
11     }
12     myException(const myException& e)
13     {
14         cout<<"copy construct"<<endl;
15     }
16     myException operator= (const myException& e)
17     {
18         cout<<"assign construct"<<endl;
19     }
20     void printMsg()
21     {
22         cout<<"myException detail massage"<<endl;
23     }
24 };
25 
26 
27  int main(int agc, char** argv)
28 {
29     try
30     {
31         myException e;
32         throw e;
33     }
34     catch (myException &e)
35     {
36         e.printMsg();
37         
38         return -1;
39     }
40     return 0;
41 }
42    
43

编译，运行

$ ./test.exe
default construct
copy construct
myException detail massage

可以看出，调用了拷贝构造，说明throw e;实际不是跑出e对象，而是其一份拷贝。

正确的是

 1 int main(int agc, char** argv)
 2 {
 3     try
 4     {
 5         //myException e;
 6          throw myException();
 7     }
 8     catch (myException &e)
 9     {
10         e.printMsg();
11         
12         return -1;
13     }
14     return 0;
15 }

执行结果如下

$ ./test.exe
default construct
myException detail massage

2，catch 的异常声明中异常对象要被声明为引用

如下非引用

 1 int main(int agc, char** argv)
 2 {
 3     try
 4     {
 5         //myException e;
 6          throw myException();
 7     }
 8     catch (myException e)
 9     {
10         e.printMsg();
11         
12         return -1;
13     }
14     return 0;
15 }
执行结果$ ./test.exe
default construct
copy construct
myException detail massage