exception handling .. more

ma740988_at_pegasus.cc.ucf.edu
Date: 12/31/04 

Date: 30 Dec 2004 20:34:39 -0800

Volume II, first chapter of the text thinking in C++ seem to indicate
that one ought to use error handling - ie throw an exception - instead
of using a host of return statements.

So now consider:

class some_exception : public std::runtime_exception {
{
some_exception ( const std::string& msg)
throw () : usrMsg(msg) { }
~some_exception ( )
throw () { }
const char *what() const throw() { return usrMsg.c_str(); }
private:
std::string usrMsg;
};

// now use some_exception
class enet_connection : public some_exception
{
public:
enet_connection() { }
~enet_connection() { }
void connect ( /args/ ) throw()
{
if ( ... )
throw some_exception ( " oops 1 " ) ;
}

void send ( /args/ ) throw()
{
if ( ... )
throw some_exception ( " oops 2 " ) ;
}
};

//Similarily
class slink_connection : public some_exception
{

};

For the purposes of discussion class enet_connection and
slink_connection refer to communication links. i.e ethernet and
starlink.

Now we're ready.
/////////////////////
class main_class
{
main_class()
: p_enet(new enet_connection()) //// 2 ////
, p_slink(new slink_connection()) //// 2 ////

{ }

void do_work()
{
try
{
p_enet->send( /args/ );
}
catch ( some_exception& excep ) { }
}
private
enet_connection* p_enet;
slink_connection* p_slink;
};

/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
If memory serves me well, the C++ FAQ's warns against the lines/items
marked //// 2 ////. The specifics I dont recall but the basic
premise surrounds the fact that the TWO (one class if I recall would be
ok ) classes (enet_connection & slink_connection) throw exceptions
which could potentiall lead to disaster when viewed in terms of
construction and 'destruction/cleanup'.

With that in mind, would it be safe to state that an alternative would
be to revise the main_class to pass in the fully constructed p_slink
and p_enet objects? So now:

int main ()
{
try {
slink_connection* p_slink = new slink_connection();
}
catch (some_exception& excep) { }

// similarily
try {
enet_connection* p_enet = new enet_connection();
}
catch ( some_exception& excep) { }

// then later
main_class* p_main_class = new main_class ( p_slink, p_enet );
}

In the end, I might have to revise the code since my advisor is not a
fan of exceptions and advises against them.

//// 2 ////
I dont recall in my readings the need to initialize a pointer to NULL
in the constructor, and check for NULL existence in the destructor.
i.e

class my_class {
public:
my_class()
: ptr_testa(NULL), ptr_testb(NULL)
{
ptr_testa = new test_classA();
prt_testb = new test_classB();
}
~my_class()
{
if (ptr_testa != NULL)
delete ptr_testa;
if (ptr_testb != NULL)
delete ptr_testb;
}
private:

test_classA* ptr_testa;
test_classB* ptr_testb;
};

Intutively this amounts to good coding style and in C++ land zero would
be preferred as opposed to null. Correct?

Just clarifying.

Relevant Pages

  • Re: How to check whether a string can be casted to be Long ?
    ... exceptions increased by a factor 2, while the test with exceptions increased ... private System.Windows.Forms.TextBox txtOutputFileName; ... private bool ValueWithinRange(string strInt) ... dTicksStart = Environment.TickCount; ...
    (microsoft.public.dotnet.framework.compactframework)
  • Re: How To: Colour Flash TextBox background?
    ... Public Sub New ... Private m_control As Control ... Public Property xControl() As Control ... > What exceptions are you expecting here? ...
    (microsoft.public.dotnet.languages.vb)
  • Re: How To: Colour Flash TextBox background?
    ... Public Sub New ... Private m_control As Control ... Public Property xControl() As Control ... > What exceptions are you expecting here? ...
    (microsoft.public.dotnet.general)
  • Re: A concern about mixing C and C++
    ... doesn't know e.g. about any exceptions that may be thrown in a function ... synonymous with forward declarations in C++ due to the differing use of ... 'struct' in a declaration, that is: ... const struct X *next} X; ...
    (comp.lang.c)
  • Re: Java needs "goto" (was Re: hi)
    ... Assemblers need "goto" but no decent HLL does. ... I don't use this construction in C either and, again, don't need it. ... Yes - but that's a result of classes that throw exceptions when their methods would be better off returning control values. ... martin@ | Martin Gregorie ...
    (comp.lang.java.programmer)