#include <string>
#include <iostream>
#include <list>
using std::cin;
using std::cout;
using std::endl;
using std::string;
using std::list;
main(){
  list<string> l;
  list<string>::iterator i;
  char buffer[81];
  while(!cin.eof()){
    cin.getline(buffer,sizeof(buffer));
    l.insert(l.end(),buffer);
    while((!cin.eof())&&cin.fail()){
      cin.clear();
      cin.ignore(80,'\n');
    }
  }
  l.sort();
  while(!l.empty()){
    i=l.begin();
    cout << *i << endl;
    l.erase(i);
  }
}

> 文字数で並び替えをする

#include <string>
#include <iostream>
#include <list>
#include <functional>

class shorter : public std::binary_function< std::string, std::string, bool >
{
public:
    bool operator()( const std::string& lhs, const std::string& rhs ) const
    {
        return lhs.size() < rhs.size();
    }
};

int main()
{
    std::list< std::string > l;

    ...

    // 文字数の昇順で並べ替え
    l.sort( shorter() );

    ...

}

// ご参考

#include <string>
#include <list>
#include <iostream>
#include <functional>
#include <algorithm>

class shorter : public std::binary_function< std::string, std::string, bool >
{
public:
    bool operator()( const std::string& lhs, const std::string& rhs ) const
    {
        return lhs.size() < rhs.size();
    }
};

int main()
{
    const std::string::size_type MAX_SIZE = 80;

    std::list< std::string > str_list;
    for( std::string s; std::getline( std::cin, s ); ){
        if( !s.empty() ){
            str_list.push_back( s.substr( 0, MAX_SIZE ) );
        }
    }

    str_list.sort();
    std::cout << "辞書順" << std::endl;
    std::copy( str_list.begin(), str_list.end(), std::ostream_iterator< std::string >( std::cout, "\n" ) );

    str_list.sort( shorter() );
    std::cout << "文字数順" << std::endl;
    std::copy( str_list.begin(), str_list.end(), std::ostream_iterator< std::string >( std::cout, "\n" ) );
}