Question

The problem.
See the below code… I was missing the return field; statement and didn’t spot it for a few debug runs. I would never have thought that something like that would get past the compiler without an error! Why did it?

Description
I have an parser object that uses std::tr1::function to have receive a translation algorithm on construction. The translation converts from a string to an object of type TransportableMessage, which is made of TMFields, which can hold different types. So anyway I made a factory function for the creation of the fields because the type of the field is based on a string (from the XML), and while there is only a few now, it may be that there are more in the future.

The tstring object is a typecast based on UNICODE and basically resolves to std::wstring at the minute. Also because I am using VS2008 unique_ptr is not there so I have hidden std::auto_ptr behind ScopedPtr_t to make an upgrade easier and thus more likely to happen.

namespace arc
{
    namespace util
    {

        int internalTest()
        {
            std::cout << "Any error?" << std::endl;
        }

        ScopedPtr_T<TMField> TmFieldFactory( const tstring& name, const tstring& typeName, const tstring& value )
        {
            ScopedPtr_T<TMField> field;
            int a = internalTest();
            if( typeName == _T("int") || typeName == _T("long") )
            {
                field.reset( new TMNumericField( name, boost::lexical_cast<__int64>(value) ) );
            }
            else if( typeName == _T("string") )
            {
                field.reset( new TMStringField( name, value ) );
            }
            else if( typeName == _T("timestamp") )
            {
                field.reset( new TMTimeField( name, boost::lexical_cast<__int64>(value) ) );
            }
            else
            {
                std::string info( __FILE__ " :: " __FUNCTION__ " : Unrecognized TmField type ");
                std::string type( typeName.begin(), typeName.end() );
                info += type;
                throw ARC_Exception( info.c_str() );
            }
            return field; // I WAS MISSING THIS!
        }
    }
}

Basically I would like to know if anyone else has had problems with this? I introduced the function internalTest to see if the problem was specific to scoped_ptrs but it appears that it is not. I also tried using internalTest in GCC and it returned an error.
Why did it Visual Studio not flag this? Am I missing a compilation setting somewhere that I can turn on? Does the standard allow this? Apologies if this is something well known, I did google and look for answers here.

EDIT:: Calling Code – Just adding this for more context.

SharedPtr_T<TransportableMessage> strToTmConvFunc_Default_Apc7_0(const std::string& tm_str)
{
    pugi::xml_document xmlDoc;
    if( false == xmlDoc.load( tm_str.c_str() ) )
    {
        ARC_LOG(LOG_WARN, "The passed TM object was malformed. %s", tm_str.c_str() );
        throw ARC_Exception( "Malformed Transportable Message XML" );
    }

    pugi::xml_node tmBase = xmlDoc.first_child();
    std::string xmlRootName( tmBase.name() );
    if( xmlRootName.compare("TM") != 0 )
    {
        ARC_LOG(LOG_WARN, "The passed TM object was malformed. %s", tm_str.c_str() );
        throw ARC_Exception( "Malformed Transportable Message XML" );
    }

    std::string tmname = tmBase.child("N").child_value();
    std::string entity = tmBase.child("E").child_value();
    ARC_LOG(LOG_INFO, "TM message received for parsing. TM name is %s", tmname.c_str() );

    tstring t_tmname( tmname.begin(), tmname.end() );
    SharedPtr_T<TransportableMessage> tm_obj( new TransportableMessage( t_tmname, 0 ) );

    pugi::xml_node fields = tmBase.child("FS");
    for( pugi::xml_node field = fields.first_child(); field; field = field.next_sibling("field") )
    {
        tm_obj->addField( arc::util::TmFieldFactory( field.child_value("N"), field.child_value("T"), field.child_value("V") ) );
    }

    return tm_obj;
}

Answer 1

Falling off the body of a function without returning something is not an error, it is undefined behavior; see 6.3.3 The return statement [stmt.return] §3:

Flowing off the end of a function is equivalent to a return with no value; this results in undefined behavior in a value-returning function.