3.3 Operations Common to All Containers

The following operations are common to all the container classes (as well as the string class):

• The equality (==) and inequality (!=) operators return true or false.

• The assignment (=) operator copies one container into another.

• empty() returns true if the container holds no elements.

• size() returns a count of the elements currently held within the container.

• clear() deletes all the elements.

The following function exercises each of these operations:

void comp( vector<int> &v1, vector<int> &v2 ) 


{ 


      // are the two vectors equal? 


      if ( v1 == v2 ) 


           return; 





      // is either vector empty? 


      if ( v1.empty() || v2.empty() ) return; 





      // no point defining it unless we are going to use it! 


      vector<int> t; 





      // assign t the largest vector 


      t = v1.size() > v2.size() ? v1 : v2; 





      // ... use t ... 





      // ok. empty t of its elements 


      // t.empty() will now return true 


      // t.size() will now return 0 


      t.clear(); 





      // ... ok, fill up t and use it some more ... 


} 

Each container supports a begin() and an end() operation to return, respectively, an iterator to the first element of the container, and 1 past the last valid element:

• begin() returns an iterator to the first element.

• end() returns an iterator that addresses 1 past the last element.

Typically, we iterate across a container starting at begin() and stopping when we reach end(). All containers support an insert() operation to add elements and an erase() operation to delete elements.

• insert() adds one or a range of elements to a container.

• erase() deletes one or a range of elements from a container.

The behavior of insert() and erase() vary depending on whether the container is sequential or associative. Sequential containers are discussed in the next section.