程序代码：

#include <vector>
#include <deque>
#include <map>
#include <set>
#include <list>
#include <iostream>
#include <fstream>
    using namespace std;

vector<string> * retrieve_text();
vector <string> *retrieve_text()
{
    string file_name ,retrieve_text_line ;
    vector<string>* retrieve_text_lines;   
    cout << "input file name, please!\n";
    cin >> file_name;
    ifstream in_file(file_name.c_str(),ios::in);
    if ( !in_file )
        {cout << "file name error! unable open the file \""<< file_name << "\"\n\n"; exit(-1);}
    else
        cout << "opened the file \""<< file_name << "\"successful\n\n";
    retrieve_text_lines = new vector <string>;
    pair<string::size_type,string::size_type> longest_line;
    string::size_type line_num = 0 ;   
    while (getline(in_file,retrieve_text_line,'\n'))
    {
        cout << "read word: " << retrieve_text_line <<"\n";
        if ( longest_line.second < retrieve_text_line.size() )
            {
                longest_line.second = retrieve_text_line.size();
                longest_line.first = line_num;
            }
        retrieve_text_lines->push_back(retrieve_text_line);       
        line_num ++;
    }
}
int main()
{
    retrieve_text();
    return 0;
}