How to resolve a name collision between a C++ namespace and a global function?

Question

if I define a namespace log somewhere and make it accessible in the global scope, this will clash with double log(double) from the standard c

Answer 1

I'd suggest:

foo::log::Log x; // Your logging class
::log(0.0); // Log function

Generally I wouldn't write using namespace foo; as there is no point having it in the foo namespace if you're not going to use it and it pollutes the global namespace.

See this related question:
How do you properly use namespaces in C++?