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In article 41C67EA6@ecid.cig.mot.com, Joe Walker <walkerjj@ecid.cig.mot.com> writes:
>
>As I understand the DWP this is legal:
>
>  void func () throw ()
>  {
>    throw 1;
>  }
>
>The question is, why?
>Surely this should be a compiler error.

It is an error if the throw statement is executed, but not otherwise.
That is, "func" might not ever be called.

That may sound like nit-picking, but it avoids having to 
decide whether examples like the following are valid:

void f1(int j) throw()
{
	if( j == 0 )
		throw 1; // the programmer believes j is always > 0
}

#include <math>
void f2(unsigned x) throw()
{
	if( std::sqrt((double)x) ) < 0.0 )
		throw 1; // really can't happen, but must compiler deduce that?
}

---
Steve Clamage, stephen.clamage@eng.sun.com




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Joe Walker (walkerjj@ecid.cig.mot.com) wrote:

|> As I understand the DWP this is legal:

|>   void func () throw ()
|>   {
|>     throw 1;
|>   }

|> The question is, why?
|> Surely this should be a compiler error.

|> What is the justification for this?

Basically for the same reason that returning a reference to a local
variable isn't a compiler error.  It is practically impossible for the
compiler to detect in the general case, and practically impossible to
find wording exact enough for a standard to define when it must be
detected by the compiler, and when the compiler is not required to
detect it.

Consider the following:

	extern void g( int ) throw (int ) ;

	void
	f() throw()
	{
		g( 0 ) ;
	}

Should the compiler complain here?  Apparently, f() may throw an
exception (through g).  But suppose in fact that I know that g cannot
throw an exception if the parameter is 0.  Should I still be required to
enclose it in a try block, to shut up the compiler?

In the direct case that you give as an example, I would imagine that any
reasonable compiler will generate a warning, the same as they do if you
blatantly return the address of a local variable.  (Note that in both
cases, there are potentially reasons why you might *want* to do this.)
-- 
James Kanze           (+33) 88 14 49 00          email: kanze@gabi-soft.fr
GABI Software, Sarl., 8 rue des Francs Bourgeois, 67000 Strasbourg, France
Conseils, études et réalisations en logiciel orienté objet --
              -- A la recherche d'une activité dans une region francophone


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  Contact address: std-c++-request@ncar.ucar.edu.  The moderation policy
  is summarized in http://dogbert.lbl.gov/~matt/std-c++/policy.html. ]