The visibility namespace attribute
The visibility namespace attribute is a language extension that allows you to control whether and how the entities within a namespace defined in one module can be referenced or used in other modules. By using this feature, you can make a shared library smaller and decrease the possibility of symbol collision. For details, see Using visibility attributes.
visibility namespace attribute syntax >>-namespace----identifier----__attribute__---------------------> >--((--+-visibility-----+--(--+-"default"---+--)--))------------> '-__visibility__-' +-"protected"-+ +-"hidden"----+ '-"internal"--' >--{--namespace_body--}----------------------------------------><
You can specify the attribute name visibility with or without leading and trailing double underscore characters; however, using the double underscore characters reduces the likelihood of name conflicts with macros of the same name.
Example
In the following example, function fun() is
defined in namespace A , and the visibility attribute
of fun() is default:
namespace A __attribute__((visibility("default"))) {
void fun(){}
}
