C++编程思想 第2卷 第1章 异常处理 清理 函数级的try块

由于构造函数能抛出异常，希望处理在对象的成员在其基类子对象被初始化的
时候抛出的异常

构造函数初始化部分的try块是构造函数的函数体，而相关的catch块紧跟着
构造函数的函数体

//: C01:InitExcept.cpp {-bor}
// From "Thinking in C++, Volume 2", by Bruce Eckel & Chuck Allison.
// (c) 1995-2004 MindView, Inc. All Rights Reserved.
// See source code use permissions stated in the file 'License.txt',
// distributed with the code package available at www.MindView.net.
// Handles exceptions from subobjects.
#include <iostream>
using namespace std;

class Base {
  int i;
public:
  class BaseExcept {};
  Base(int i) : i(i) { throw BaseExcept(); }
};

class Derived : public Base {
public:
  class DerivedExcept {
    const char* msg;
  public:
    DerivedExcept(const char* msg) : msg(msg) {}
    const char* what() const { return msg; }
  };
  Derived(int j) try : Base(j) {
    // Constructor body
    cout << "This won't print" << endl;
  } catch(BaseExcept&) {
    throw DerivedExcept("Base subobject threw");;
  }
};

int main() {
  try {
    Derived d(3);
  } catch(Derived::DerivedExcept& d) {
    cout << d.what() << endl;  // "Base subobject threw"
  }
  getchar();
} ///:~

在Derived类的构造函数中，初始化列表处在关键字try和构造函数的函数体
之间。
如果构造函数发生异常，Derived类所包含的对象也就没有构造完成，因此
程序返回到创建该对象代码的地方是没有意义的

输出
Base subobject threw

C++允许在所有函数中使用函数级try块

//: C01:FunctionTryBlock.cpp {-bor}
// From "Thinking in C++, Volume 2", by Bruce Eckel & Chuck Allison.
// (c) 1995-2004 MindView, Inc. All Rights Reserved.
// See source code use permissions stated in the file 'License.txt',
// distributed with the code package available at www.MindView.net.
// Function-level try blocks.
// {RunByHand} (Don't run automatically by the makefile)
#include <iostream>
using namespace std;

int main() try {
  throw "main";
} catch(const char* msg) {
   cout << msg << endl;
   return 1;
   getchar();
} ///:~

这种情况，catch块中的代码可以想函数体中的代码一样正常返回

输出
main

在vs里面会闪一下窗口 之后关闭