IANAL, but nearly any recorded/written down is copyrightable. However ideas are not. If you implement from pseuso-code, it is another expression of the same idea. Different forms of expression have different rules on how different the new work must be to be unique. If you copied a function and just changed the variable names, it could be argued that it was an infringement.

If you copy a compilable function and give attribution, probably no one will care. If you copy a whole enterprise system, they might. If the original author cares, there should be a rights notification in the code. In particular Wikipedia articles have the GNU Free Documentation license, so you are pretty safe there.