When does a name clash occur in c plus plus?

Answer 1

Name clashes occur whenever you re-use the same name within the same scope. For instance, if you declare a variable with the name v, you cannot declare another variable v while the previous instance remains in scope. You can, however, nest one scope within another and re-use the same name. In this case, the original name is shadowed: it remains in scope but is not accessible within the nested scope. When the nested scope falls from scope, the original name becomes visible again.

Name clashes often occur when you use directives such as using namespace std; at namespace scope and particularly in header files, where common names (such as list or vector) can easily clash with namespace entities (such as std::list or std::vector). Directives such as these should be used sparingly and appropriately, ideally scoped to the functions and classes that actually use them in order to minimise unnecessary coupling.