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Language: C++
Expertise: Advanced

Oct 14, 1999

To some extent, the use of fully qualified names is the recommended way of referring to namespace members because it uniquely identifies and yet it avoids name conflicts. For example:

 
  #include <string>
  int main()
  {
    std::string str;
    std::string str2;
  }

In the example above, the fully qualified name std::string is used twice. In real world code, however, dozens of components of the Standard Library are used. Repeating their qualified names over and over again is laborious and error-prone. Worse yet, it renders your code unreadable. When you need to use qualified names more than 2-3 times, prefer a using-declaration or even a user-directive:

 
  #include <string>
  #include <vector>
  int main()
  {
    using std::string; //using declaration; 
needed only once 
    using std::vector; // using declaration 
    string str; // non-qualified name 
    string str2;
    vector <int> vi;
  }