I have come across this prpblem twice now when trying to link third party libraries to my program. All the links are correct however I receive the following very strange error:

"declaration does not declare anything)"

This refers to the following line of code in a header file belonging to the third party library:

virtual Int_t Fill(Axis_t x);

Now I believe that this line is declaring a virtual method called Fill which takes an object of type Axis_t and returns an object of type Int_t. I see no problem with the syntax or declaration.
I wonder if I am possible ommitting to include a header file which might solve this problem.

On the other hand has anybody come across anything similar which might help?

Tristan

This function is probably declared outside of a class (such as in a global scope or in a function body). If the compiler says it doesn't do you any good, then it probably doesn't, but I'd leave it and notify the code maintainer in case it should be something else. It might be a hidden bug that no one has caught, or it might be something that otherwise means something to a different compiler. If your implementation works without it, you should leave it. In any case, be sure that the error isn't a result of your implementation, then notify the source of the code.
ta0kira

PS Are you using gcc with the -Wall flag?

Thanks. The decleration actually does occur inside a class. I have posted to a forum belonging to one application where this occurred and I will see what happens.

I am using gcc. What is the significance of the -Wall flag?

Tristan

You're using gcc or g++? Virtual functions and classes are a C++, not C thing. I believe a C compiler wouldn't know what to do with them...

The -Wall switch turns on all warnings that might otherwise be hidden.

I thought that g++ was part of the gcc compiler suite. I was under the impression that gcc was the GNU compiler and could compile a number of different languages. I assumed that g++ was the C++ part of gcc.

Am I right here? If not how does it really work?

g++ and gcc can both compile C++. g++ is just a version that looks for includes in different places and links to different libs; if your code doesn't use std includes, then gcc should compile and link it fine.

If it's in a class, it might be the declaration of x (isn't needed; could just say Fill(Axis_t) since the function isn't defined here.) Otherwise the function might not be defined for this class. Just as a test, change it to "virtual Int_t Fill(Axis_t x) = 0;" and see if you get a compiler error and post what happens (I have a few ideas dependent on what the result is.)

The -W flag is for warnings, and "all" denotes all warnings, so -Wall means you will get every warning possible.
ta0kira