Leon Anavi
IT Tips && Tricks

C/C++

Created: 31.08.2009 23:29 Last Modified: 31.08.2009 23:29 Views: 4765
Keywords: container, iterator, STL, vector

STL Containers: Vector

Purpose of the STL Vector

Vectors are STL (Standard Template Library) containers that support both direct and consecutive access to elements. Vectors support all the features of the native C++ arrays but have some advantages. Vectors are implemented as dynamic arrays so they can change their size automatically. The STL Vector is a template class so it supports multiple data types: all native C++ types and user defined types, structures and classes.

Tricks with Vectors

Add a New Element

  • Add an element to the end of the vector
  • The method push_back is used to add an element to the end of the container.
    #include <iostream>
    #include <vector>
    int main(int argc, char** argv)
    {
            std::vector<int> MyVector;
            MyVector.push_back(1);
            std::cout << MyVector[0] << std::endl;
            return 0;
    }
    
  • Add an element at certain position
  • The method insert should be used to extend the vector by adding a new element at a certain position
    #include <iostream>
    #include <vector>
    int main(int argc, char** argv)
    {
            std::vector<int> MyVector;
            //Add an element at the beginning with value 1
            std::vector<int>::iterator Iter;
            Iter = MyVector.begin();
            MyVector.insert(Iter,1);
            std::cout << MyVector[0] << std::endl;
            return 0;
    }
    

Delete an Element

  • Delete an element at the end of the vector
  • The method pop_back should be used to remove an element at the end of the vector.
    #include <iostream>
    #include <vector>
    int main(int argc, char** argv)
    {
            std::vector<int> MyVector;
            MyVector.push_back(1);
            MyVector.pop_back();
            std::cout << MyVector.empty() << std::endl;
            return 0;
    }
    
    The example add an element and after that deletes it. The execution of the application will result in 1 (true) because the vector will be empty.
  • Delete an element at a certain position
  • The method erase should be used to remove a certain element.
    #include <iostream>
    #include <vector>
    int main(int argc, char** argv)
    {
            std::vector<int> MyVector;
            MyVector.push_back(11);
            MyVector.push_back(21);
            std::vector<int>::iterator Iter;
            //Delete the first element
            Iter = MyVector.begin();
            MyVector.erase( Iter );
            //Show the first element (aka the second before calling erase)
            Iter = MyVector.begin();
            std::cout << *Iter << std::endl;
            return 0;
    }
    
  • Delete All Elements
  • To truncate the vector call clear.
    #include <iostream>
    #include <vector>
    int main(int argc, char** argv)
    {
            std::vector<int> MyVector;
            MyVector.push_back(11);
            MyVector.push_back(21);
            //Remove all elements
            MyVector.clear();
            std::cout << MyVector.empty() << std::endl;
            return 0;
    }
    

Access to Elements of a STL Vector

  • Loop through Elements with an Iterator
  • #include <iostream>
    #include <vector>
    typedef std::vector<int> VectorInt;
    typedef VectorInt::iterator VectorIntIter;
    int main(int argc, char** argv)
    {
            VectorInt MyVector;
            MyVector.push_back(11);
            MyVector.push_back(21);
            MyVector.push_back(31);
            for(VectorIntIter Iter = MyVector.begin(); Iter < MyVector.end(); Iter++)
            {
                    std::cout << *Iter << std::endl;
            }
            return 0;
    }
    
  • Direct Element Access
  • #include <iostream>
    #include <vector>
    typedef std::vector<int> VectorInt;
    int main(int argc, char** argv)
    {
            VectorInt MyVector;
            MyVector.push_back(11);
            MyVector.push_back(21);
            MyVector.push_back(31);
            int nSize = MyVector.size();
            for(int nIter=0; nIter < nSize; nIter++)
            {
                    std::cout << MyVector[nIter] << std::endl;
            }
            return 0;
    }
    

Class Reference

C++ : Reference : STL Containers : vector
C++ Vectors


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