To capitalize the entire string type string

#include <algorithm>
#include <string>

std::string str = "Hello World";
std::transform(str.begin(), str.end(),str.begin(), ::toupper);

template< class InputIt, class OutputIt, class UnaryOperation >
OutputIt transform( InputIt first1, InputIt last1, OutputIt d_first,
                    UnaryOperation unary_op );

//or

template< class InputIt1, class InputIt2, class OutputIt, class BinaryOperation >
OutputIt transform( InputIt1 first1, InputIt1 last1, InputIt2 first2, 
                    OutputIt d_first, BinaryOperation binary_op );

#include <boost/algorithm/string.hpp>
#include <string>

std::string str = "Hello World";
boost::to_upper(str);
std::string newstr = boost::to_upper_copy<std::string>("Hello World");