Re: [Discuss-gnuradio] Problem with undefined symbol in new block created by gr_modtool in 3.7.2

[Martin Braun]

On 05.03.2014 22:44, Nowlan, Sean wrote:
> The first place I'd look is in your_block.h. Did you remember to
> declare any public member functions to be pure virtual in that file,
> and then declare your (non-virtual) functions in your_block_impl.h?
> If you forgot to declare pure virtual functions, i.e., "virtual
> return_type your_block(args_list) = 0;" in your_block.h, it will
> compile but you will get the undefined symbol at runtime.
>
> This probably a common pitfall and it might be worth making a note in
> the wiki for OutOfTreeModules. I'll add that.
>
> Architects of gr_modtool... can you add an autogen comment in *.h
> files reminding the user to declare pure virtual functions? I think
> users who don't deeply understand OO and particularly its  C++ syntax
> would benefit from this reminder. I think it's a common paradigm to
> use other examples to fill in the "guts" of gr_modtool generated C++
> code, but things like this are easy to miss.

Disciples of gr_modtool...
When you create a block w/ modtool, it has zero public methods (except 
for make(), which is arguably special, and gets auto-created in the 
impl.cc file).

So if I put in a reminder, it will actually remind people before there's 
a reason to declare a function, which might confuse people.
Perhaps a more general instruction on how to add public methods would be 
good, though.
I'll think about this.

M