C++异常(3) - 捕获基类与子类的异常

如果基类和子类都被做为异常捕获，则子类的catch代码块必须出现在基类之前。
如果把基类放在前面，则子类的catch代码块永远都不会被调用。

例如，下面程序打印“Caught Base Exception”。

#include<iostream>
using namespace std;
class Base {};
class Derived: public Base {};
int main()
{
   Derived d;
   try {
       throw d;
   }
   catch(Base b) {
        cout<<"Caught Base Exception";
   }
   catch(Derived d) {  //这个catch代码块永远都不会被执行
        cout<<"Caught Derived Exception";
   }
   return 0;
}

上述程序中，如果调整下声明的顺序，则都可以被捕获。

下面是修改之后的程序，会打印“Caught Derived Exception”。

#include<iostream>
using namespace std;
 
class Base {};
class Derived: public Base {};
int main()
{
   Derived d;

   try {
       throw d;
   }
   catch(Derived d) {
        cout<<"Caught Derived Exception";
   }
   catch(Base b) {
        cout<<"Caught Base Exception";
   }
   return 0;
}

Java中, 编译器不允许在子类之前捕获基类的异常。C++中，编译器会给出类似下面的警告，但是还是可以编译成功。

visual studio 2015会提示： "warning C4286: “Derived”: 由基类(“Base”)在行 17 上捕获"

例如，下面Java代码会编译失败， “exception Derived has already been caught”

//文件保存为Main.java
class Base extends Exception {}
class Derived extends Base  {}
public class Main {
  public static void main(String args[]) {
    try {
       throw new Derived();
    }
    catch(Base b) {}
    catch(Derived d) {}
  }
}

来源：CSDN

作者：水草

链接：https://blog.csdn.net/shltsh/article/details/46039417

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base