NetNews Usenet Archive 1992 #19/NN_1992_19.iso/spool/comp/lang/cplus/12901

Text File | 1992-08-25 | 1.9 KB | 59 lines

Path: sparky!uunet!wupost!sdd.hp.com!uakari.primate.wisc.edu!ames!pacbell.com!well!johnrp
From: [e-mail] (John Panzer)
Newsgroups: comp.lang.c++
Subject: Re: break/continue (was: Re: Tiny proposal for named loops.)
Message-ID: <[e-mail]>
Date: 26 Aug 92 06:12:07 GMT
References: <[e-mail]> <rmartin.714756719@thor> <[e-mail]>
Sender: [e-mail]
Organization: Whole Earth 'Lectronic Link
Lines: 47

In article <[e-mail]> uunet.ca!frumious!pat writes:
>[e-mail] (Bob Martin) writes:
>
>|No, exceptions do not violate structure (IMHO).  The function which
>|throws an exception never returns!  The calling code preserves its
>|invariants.  The exception is caught by code which expects it, so its
...(deleted)
>An error function that stops your program alters the control flow
>in a nice, simple way.  By contrast, exceptions can have somewhat
>non-intuitive effects.  Consider this function:
>
>   void foo() {
>      char* p = new char[17];
>      doSomething();
>      delete [] p;
>   };
>
>If doSomething() can throw an exception, then foo() has a memory leak!

If doSomething() calls exit(), the program still has a memory leak.
(Usually the memory is reclaimed by the system so you don't notice,
but try it with shared memory sometime...)  On the other hand,
in the presence of exceptions you have at least two ways to plug
the leak:

  void foo() {
    char * p = new char[23];
    try {doSomething();}
    catch(...) {delete p; throw;}
    delete p;
  }

Or, make a "resource acquisition" class:

  template <class T> class HeapArray {
  public:
    HeapArray(size_t NumElems) {Ptr = new T[NumElems];}
    ~HeapArray(void) {delete Ptr;}
    T * Ptr;
  };
  void foo() {
    HeapArray<char> p(5);
    doSomething();
  } // p is destructed whether or not exception is thrown.

John Panzer
[e-mail]