Namespaces

From 554fd8c5195424bdbcabf5de30fdc183aba391bd Mon Sep 17 00:00:00 2001 From: upstream source tree Date: Sun, 15 Mar 2015 20:14:05 -0400 Subject: obtained gcc-4.6.4.tar.bz2 from upstream website; verified gcc-4.6.4.tar.bz2.sig; imported gcc-4.6.4 source tree from verified upstream tarball. downloading a git-generated archive based on the 'upstream' tag should provide you with a source tree that is binary identical to the one extracted from the above tarball. if you have obtained the source via the command 'git clone', however, do note that line-endings of files in your working directory might differ from line-endings of the respective files in the upstream repository. --- libstdc++-v3/doc/html/manual/using_namespaces.html | 61 ++++++++++++++++++++++ 1 file changed, 61 insertions(+) create mode 100644 libstdc++-v3/doc/html/manual/using_namespaces.html (limited to 'libstdc++-v3/doc/html/manual/using_namespaces.html') diff --git a/libstdc++-v3/doc/html/manual/using_namespaces.html b/libstdc++-v3/doc/html/manual/using_namespaces.html new file mode 100644 index 000000000..ffd6c6f63 --- /dev/null +++ b/libstdc++-v3/doc/html/manual/using_namespaces.html @@ -0,0 +1,61 @@ + + +Namespaces

Namespaces
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Namespaces

Available Namespaces

There are three main namespaces. +

std
The ISO C++ standards specify that "all library entities are defined +within namespace std." This includes namespaces nested +within namespace std, such as namespace +std::tr1. +
abi
Specified by the C++ ABI. This ABI specifies a number of type and +function APIs supplemental to those required by the ISO C++ Standard, +but necessary for interoperability. +
__gnu_
Indicating one of several GNU extensions. Choices +include __gnu_cxx, __gnu_debug, __gnu_parallel, +and __gnu_pbds. +

A complete list of implementation namespaces (including namespace contents) is available in the generated source documentation. +

namespace std

+ One standard requirement is that the library components are defined + in namespace std::. Thus, in order to use these types or + functions, one must do one of two things: +

put a kind of using-declaration in your source +(either using namespace std; or i.e. using +std::string;) This approach works well for individual source files, but +should not be used in a global context, like header files. +
use a fully +qualified name for each library symbol +(i.e. std::string, std::cout) Always can be +used, and usually enhanced, by strategic use of typedefs. (In the +cases where the qualified verbiage becomes unwieldy.) +

Using Namespace Composition

+Best practice in programming suggests sequestering new data or +functionality in a sanely-named, unique namespace whenever +possible. This is considered an advantage over dumping everything in +the global namespace, as then name look-up can be explicitly enabled or +disabled as above, symbols are consistently mangled without repetitive +naming prefixes or macros, etc. +

For instance, consider a project that defines most of its classes in namespace gtk. It is possible to + adapt namespace gtk to namespace std by using a C++-feature called + namespace composition. This is what happens if + a using-declaration is put into a + namespace-definition: the imported symbol(s) gets imported into the + currently active namespace(s). For example: +

+namespace gtk
+{
+  using std::string;
+  using std::tr1::array;
+
+  class Window { ... };
+}
+

+ In this example, std::string gets imported into + namespace gtk. The result is that use of + std::string inside namespace gtk can just use string, without the explicit qualification. + As an added bonus, + std::string does not get imported into + the global namespace. Additionally, a more elaborate arrangement can be made for backwards compatibility and portability, whereby the + using-declarations can wrapped in macros that + are set based on autoconf-tests to either "" or i.e. using + std::string; (depending on whether the system has + libstdc++ in std:: or not). (ideas from + Llewelly and Karl Nelson) +

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