User kokos answered the wonderful Hidden Features of C# question by mentioning the using keyword. Can you elaborate on that? What are the uses of using?
The using statement is used to work with an object in C# that implements the IDisposable interface. The IDisposable interface has one public method called Dispose that is used to dispose of the object.
183 In C++11, the using keyword when used for type alias is identical to typedef. 7.1.3.2 A typedef-name can also be introduced by an alias-declaration. The identifier following the using keyword becomes a typedef-name and the optional attribute-specifier-seq following the identifier appertains to that typedef-name.
In other word, if you know that the initialization of a variable in using may throw a particular exception, I wrap it with try-catch. Similarly, if within using body something may happen, which is not directly related to the variable in using, then I wrap it with another try for that particular exception. I rarely use Exception in my catch es.
The problem with putting using namespace in the header files of your classes is that it forces anyone who wants to use your classes (by including your header files) to also be 'using' (i.e. seeing everything in) those other namespaces. However, you may feel free to put a using statement in your (private) *.cpp files.
Updating the using keyword was specifically for templates, and (as was pointed out in the accepted answer) when you are working with non-templates using and typedef are mechanically identical, so the choice is totally up to the programmer on the grounds of readability and communication of intent.
In a MySQL JOIN, what is the difference between ON and USING()? As far as I can tell, USING() is just more convenient syntax, whereas ON allows a little more flexibility when the column names are not
But if you put the using declaration inside a namespace it's limited to the scope of that namespace, so is generally OK (with the usual caveats on your particular needs and style).
Yes Yes. Either way, when the using block is exited (either by successful completion or by error) it is closed. Although I think it would be better to organize like this because it's a lot easier to see what is going to happen, even for the new maintenance programmer who will support it later:
When you make a call to using namespace <some_namespace>; all symbols in that namespace will become visible without adding the namespace prefix. A symbol may be for instance a function, class or a variable. E.g. if you add using namespace std; you can write just cout instead of std::cout when calling the operator cout defined in the namespace std. This is somewhat dangerous because namespaces ...
