C++: Should I use 'typedef' or 'using namespace'?
c++, namespaces, using-directives
Solution
The two options you state are not equivalent. This one:
using namespace project1::namespace1;
pulls in everything from the namespace, giving you little control and making clashes likely. I see only cons, and no pros here.
But you don't need to use a `typedef` to bring in a single symbol, you can use
using project1::namespace1::class1;
Whether you use this or the `typedef` doesn't make too much of a difference. But bear in mind that `typedef` is limited to types and enumerations, whereas `using` can refer to values, functions, etc:
namespace X {
const int x{42};
enum Fruit{Apple, Pear};
}
using X::x; // OK
typedef X::x xx; // Error! 'x' in namespace 'X' does not name a type
so the two expressions are not completely equivalent.
Problem
I am writing a library with mutiple dependent modules. When I include a file from a different module, should I resolve the namespace with: ``` using namespace project1::namespace1; class1 obj; ``` or ``` typedef project1::namespace1::class1 class1; class1 obj; ``` What are the pros/cons of each approach? I read somewhere that we should use `typedef` in .H files and `using` in .C files, is this advisable? One problem I have encountered with 'typedef' is it leads to namespace ambiguity if I include both original class and the class with 'typedef' in a third module.