Re: safer stl

From: Chris Val (chrisval_at_bigpond.com.au)
Date: 07/13/04 

Date: 13 Jul 2004 02:30:57 -0700

"SaltPeter" <SaltPeter@Jupiter.sys> wrote in message news:<6XoIc.1300$TB3.183112@news20.bellglobal.com>...
> "Edo" <edwardoJE@aking.com> wrote in message
> news:40f1ec6c@dnews.tpgi.com.au...
> > Hello
> > since the STL does not use error handling, there have been "safe" STL
> > introduced, is that something that I should use at least during software
> > development?
> > e.g. somthing like STLport or safeSTL by Cay Horstmann.

[snip]

> As far as error handling is concerned, returning a bool as an error
> condition from some function when an error occurs is the old way.

It has definately been used for a long while - there is no
doubting that, but returning a boolean value is still quite
useful in many circumstances.

In regards to your post, I have a few corrections to make,
and few opinions to throw - I hope you don't mind ? :-).
 
> Exceptions are designed to catch errors as well as unexpected errors. Take
> this simple rudimentary example of how to try, throw and catch an exception
> class in response to an out_of_range vector access. Note the try block and
> the catch blocks as well as the throw statement which "throws" an instance
> of the Err class.

[snip]

> int main()
> {
> try {
>
> std::vector<int> v;
>
> v.push_back(0);
> v.push_back(1);
>
> for (int i = 0; i < 3; i++)
> {
> if(i > v.size() -1)

You are comparing signed 'vs' unsigned values between 'i'
and 'v.size()', which in turn returns:
    'std::vector<int>::size_type'.

You should change that to:
   for( std::vector<int>::size_type i; ...............

> throw Err("vector range error"); // throw...

I can understand what you were trying to demonstrate.

For the benefit of the OP and other readers, I would like
to demonstrate this taking a slightly different approach,
which makes use of the standard library, and in particular,
the features of 'std::vector' that help catch such errors.

For example, when you attempt to access a vector outside
of it's range of stored values, an *out_of_range* error
occurs naturally when accessed via the '.at(n)' member.

See my example at end of the post:

> std::cout << "v[" << i << "] = " << v[i] << std::endl;
> }
>
> return 0;
> } // end try block
>
> // Err catch block
> catch(Err& r_e)

You should try to catch by const reference, if you're
not going to attempt to modify the properties of the
exception object.

> {
> r_e.report();
> return -1;

Non portable return value.
 
It is preferable to use the 'C' macro:

  # include <cstdlib>
    return EXIT_FAILURE;

...which will return an implementation defined value.

> }
>
> // unexpected catch block
> catch(...)
> {
> std::cerr << "unknown exception generated\n";
> return -1;

Same here...
# include <cstdlib>
return EXIT_FAILURE;

> }
> }

The following example aims to demonstrate what happens, and
how to deal with errors that exceed the bounds of a std::vector.

I should also make it clear to newbies reading this, that the
'std::out_of_range' exception will only be thrown when using
the '.at(n)' member function, and not when accessing the vector
through the subscript operator '[n]'.

Here is a very quick sample I put together:

# include <iostream>
# include <ostream>
# include <vector>
# include <stdexcept>
# include <exception>

int main()
 {
  try
   {
    std::vector<int> V;

    V.push_back( 0 ); // Ok ...
    V.push_back( 1 ); // Ok ...

    V.at( 2 ) = 100; // Oops! - There is no element at
                      // the index position of '2'.
   }
  catch( const std::out_of_range& e )
   {
    std::cout << e.what() << '\n';
   }
  catch( ... )
   {
    std::cout << "Error: Unknown exception generated\n";
   }

  return 0;
 }

-- OUTPUT --
index out of range in function: vector:: at(size_t)
 index: 2 is greater than max_index: 2

Cheers.
Chris Val

Relevant Pages

  • Re: Analyzing this Progression
    ... 7ths of 7th chords resolve downward. ... No, it's not an exception. ... the lower member rises or falls. ...
    (rec.music.theory)
  • Re: When is a function not a function?
    ... a DOM element and Array or a value with falseness. ... assertion that the test betrays poor design. ... assume the worst case (that the exception will be thrown), ...
    (comp.lang.javascript)
  • Re: Is Cobol Dead? <190937416 5303721544.634709nocannedmeat.casey.obrien.r-gmail.com@news.gigane
    ... If it'd at least logged the exception, ... 88 VALID-SEX VALUES 'M' 'F'. ... for this is that CPU time Costs Money and if there's a reason not to burn ...
    (comp.lang.cobol)
  • Re: A C++ Whishlist
    ... Java is annoying enough with its exceptions to the operator overloading ... What's the point in "catching" an exception for a statement where you ... "Je ein Stueckchen Kreppsohle an die Fuesse eines Hamsters kleben. ...
    (comp.lang.cpp)
  • Re: Jon Skeets thread pooling sample
    ... that decision - I can't think of a good reason why the name of a thread has ... > 4) Add some sort of exception logging for this and the other events. ... It needs to be set before the 1st callback occurs ...
    (microsoft.public.dotnet.general)