Code in journal papers Most papers do not specify a separate license for the source code, so presumably it would be licensed under the same terms as the rest of the paper. Typically, this means that the copyright lies with the publisher. Then,


As a reader, do I need permission from the publisher to use source code contained in journal articles?
Would using the source code be considered fair use in the US? What about countries that do not have comparable laws?
As an author, what should I do if I want the code I publish to be freely usable by others?
I think the codes available in papers are provided as materials for several purposes, including


Help reviewers and journal's board to efficiently evaluate the work and identify its technical merit.
Enable readers to better grasp the algorithm/method proposed
Enable researchers to utilize the code in their future research to avoid duplication
Help (novice) researchers to play with the code for educational benefits
Provide opportunity to peers to further improve the proposal


However, you may contact the author(s) if the want to use the code for


Commercializing the algorithm/method 
Use the code for activities that generates money
Register patent using available contents


In my institute, I see lots supervisor ask their master students to read recent papers and identify a small research problem to alleviate during their project work. Students either use the given code or contact the authors for code, which authors usually provide the code.

So, I think you don't need to explicitly state the code copyright in the paper. But, if you are really interested to do that, you can have a footnote in the first page allowing readers to utilize the code in full, if the EiC does not mind.

Hope it helps