Deleting certain characters on string

[jonajonlee]

So in my class we are learning about strings. In this program, the goal is to reformat the text in a data file.

sample data file:

Here's a "TEST" file. (DateD 5 April, 2012)
Will this #*PrOGRAM+=@ that includes
!user-defined?!?> FUNCTIONS
really work? Only time will
tell.............

My program needs to delete the non alphanumeric characters that are at the beginning and end of each word.
For instance: "TEST" needs to be changed to TEST.
I can't use the isalpha to delete all nonalphanumeric characters because the ones inside each word are to be kept
For instance: !user-defined?!?> needs to be changed to user-defined

I've been trying to devise a way to do this but I can't figure this out.

Here's the code for the function.Thanks!

string characters(string text)
{
  int n=text.length();
  string newtext;
  for (int i=0; i<n; i++)
    if(isalnum(text[0])&&isalnum(text[n-1]))
      {
        newtext=newtext+text[i];
      }
    else
      {
      while (!isalnum(text[0]))
        {
        for (int j=1; j<n; j++)
          text=newtext+text[j];
        }
      while (!isalnum(text[n-1]))
        for(int k=0; k<n-2; k++)
          text=newtext+text[k];
        }
  return newtext;
}

[deceptikon]

It's really just a customized trim algorithm. Search from the beginning until you find a valid character, then mark that position. Search from the end as well until you find a valid character and mark that position. Now you have enough information to extract a substring:

#include <iostream>
#include <string>
#include <sstream>

#include <cctype>

using namespace std;

string sanitize(string const& s, int valid_character(int))
{
    string::size_type first = 0;
    string::size_type last = s.size();

    // Skip leading and trailing invalid characters
    //
    while (first != s.size() && !valid_character(s[first]))
    {
        ++first;
    }

    while (last != 0 && !valid_character(s[last - 1]))
    {
        --last;
    }

    // Trim and remove the located invalid characters (leave embedded "invalid" characters)
    return s.substr(first, last - first);
}

int main()
{
    istringstream src(
        "Here's a \"TEST\" file. (DateD 5 April, 2012)\n"
        "Will this #*PrOGRAM+=@ that includes\n"
        "!user-defined?!?> FUNCTIONS\n"
        "really work? Only time will\n"
        "tell.............");
    string word;

    while (src >> word)
    {
        cout << sanitize(word, isalnum) << '\n';
    }
}