> On 7/11/2011 1:09 PM, shath...@e-z.net wrote:
>> There are lots of places in the XALANC code where
>> using STL (Standard Template Library) interface
>> renames the type 'void' to 'result_type' and therefore
>> confuses GCC and other compilers, resulting in
>> warnings - requesting a return statement.
>>
>> A 'void' function result type means that there
>> should not be a return statement.
>>
>> The file STLHelper.hpp is just one instance in the
>> XALANC code. See: JIRA XALANC-570
>>
>> The warnings do not create bad code! I don't have
>> the time to find all such occurrences at this time.
>>
>> To maintain consistency in the code base, XALANC-570
>> should probably not be committed, maintaining
>> compatibility throughout the code base.
> These are unfortunately compiler limitations. Returning void is
> explicitly allowed by the standard for the very purpose of being able to
> write generic code like this.
>
> Can you be more explicit about which version of GCC is issuing this
> warning?
>
> Dave
>
JIRA XALANC-570
Environment:
g++ (GCC) 3.2.3 20030502 (Red Hat Linux 3.2.3-52), Intel
Should this be a problem?
STL defines the unary_function class template as:
template <typename Arg, typename Result>
struct unary_function {
typedef Arg argument_type;
typedef Result result_type;
};
The xalanc/Include/STLHelper.hpp - for example - contains:
=======
struct DeleteFunctor : public std::unary_function<const Type*, void>
{
typedef std::unary_function<const typename T::value_type&, void>
BaseClassType;
typedef typename BaseClassType::result_type result_type;
typedef typename BaseClassType::argument_type argument_type;
// Now: the typedef to result_type is actually 'void'
result_type
operator()(argument_type thePointer) const
{
makeXalanDestroyFunctor(thePointer)(thePointer, m_memoryManager);
}
// The makeXalanDestroyFunctor(thePointer)(thePointer, m_memoryManager)
// evaluates to a function that has as 'void' return type.
private:
MemoryManager& m_memoryManager;
}
=======
The GNU gcc/g++ 3.2.3 compiler complains that 'result_type' for operator()
is non-void and therefore wants the line to have a return:
return makeXalanDestroyFunctor(thePointer)(thePointer, m_memoryManager);
C/C++ standard says that functions declared as 'void' return type
should not have a return statement.
It is unclear what happens to C/C++ compilers and linkers
when the following is actually coded:
return void;
Note: A 'void' return type means there is no return value.
Interpreting the result of (return void;) may be undefined
garbage instead of zero or null.
The problem here is that the GNU gcc/g++ compiler either looses
track of 'void' type across typedef, or cannot find the
'void' return type when using a function set selector such as
makeXalanDestroyFunctor(thePointer).
The fix to resolve the return type warnings where 'void'
is known is to explicitly specify 'void' as the result_type
on a STL operator() definition.
Sincerely,
Steven J. Hathaway
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