C why use namespaces

Using should be used with great care because it effectively import one or all symbols from a namespace into your current namespace. This is evil to do it in a header file because your header will pollute every source including it it reminds me of macros You'll see a lot of "using namespace std ;" in tutorial or example codes.

The reason is to reduce the number of symbols to make the reading easier, not because it is a good idea. Namespaces are more than packages. In the "Special Edition", at 8. Namespace declarations can be nested within another namespace.

Public or private No need to give semicolon after the closing brace of definition of namespace. We can split the definition of namespace over several units.

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Email Address:. Sign me up! Skip to content. About Post index Higher-level C Project Namespaces in C Posted on January 24, by ejrh. Reified namespaces with structs Can we separate the namespace from the name by something more tangible than a few characters? Efficiency considerations Using the first implementation of a namespace, as a static variable in a header file, means that each compilation unit that includes that header gets its own private copy. Like this: Like Loading This entry was posted in Higher-level C and tagged c , namespace , struct.

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Name required. Search for:. An example of this is the std namespace which is declared in each of the header files in the standard library. Members of a named namespace can be defined outside the namespace in which they are declared by explicit qualification of the name being defined.

However, the definition must appear after the point of declaration in a namespace that encloses the declaration's namespace. For example:. This error can occur when namespace members are declared across multiple header files, and you have not included those headers in the correct order.

If an identifier is not declared in an explicit namespace, it is part of the implicit global namespace. In general, try to avoid making declarations at global scope when possible, except for the entry point main Function , which is required to be in the global namespace. To explicitly qualify a global identifier, use the scope resolution operator with no name, as in ::SomeFunction x ;.

This will differentiate the identifier from anything with the same name in any other namespace, and it will also help to make your code easier for others to understand.

Namespaces may be nested. An ordinary nested namespace has unqualified access to its parent's members, but the parent members do not have unqualified access to the nested namespace unless it is declared as inline , as shown in the following example:.

Ordinary nested namespaces can be used to encapsulate internal implementation details that are not part of the public interface of the parent namespace. In contrast to an ordinary nested namespace, members of an inline namespace are treated as members of the parent namespace. This characteristic enables argument dependent lookup on overloaded functions to work on functions that have overloads in a parent and a nested inline namespace.

It also enables you to declare a specialization in a parent namespace for a template that is declared in the inline namespace.