C++ writing a function that extracts words from a paragraph - c++

Question

The program I am writing reads a text file, breaks the paragraph into individual words, compares them to a list of "sensitive words" and if a word from the text file matches a word from the Sensitive word list, it is censored. I have wrote functions that find the beginning of each word, and a function that will censor or replace words on the Sensitive word list with "#####" (which I left out of this post). A word in this case is any string that contains alphanumeric characters.
The function I am having trouble with is the function that will "extract" or return the individual words to compare to the sensitive word list (extractWord). At the moment it just returns the first letter of the last word in the sentence. So right now all the function does is return "w". I need all the individual words.
Here is what I have so far ...
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
bool wordBeginsAt (const std::string& message, int pos);
bool isAlphanumeric (char c); //
std::string extractWord (const std::string& fromMessage, int beginningAt);
int main()
{
string word = "I need to break these words up individually. 12345 count as words";
string newWord;
for (int i = 0; i < word.length(); ++i)
{
if (wordBeginsAt(word, i))
{
newWord = extractWord(word, i);
}
}
//cout << newWord; // testing output
return 0;
}
bool wordBeginsAt (const std::string& message, int pos)
{
if(pos==0)
{return true;}
else
if (isAlphanumeric(message[pos])==true && isAlphanumeric(message[pos- 1])==false)
{
return true;
}
else
return false;
}
bool isAlphanumeric (char c)
{
return (c >= 'A' && c <= 'Z')
|| (c >= 'a' && c <= 'z')
|| (c >= '0' && c <= '9');
}
std::string extractWord (const std::string& fromMessage, int beginningAt)
{
string targetWord= "";
targetWord = targetWord + fromMessage[beginningAt];
return targetWord;
}
edit: after trying to use targetWord as an array (which I couldn't define the size) and using several different for and while loops within extractWord I found a solution:
std::string extractWord (const std::string& fromMessage, int beginningAt)
{
string targetWord= "";
while (isAlphanumeric(fromMessage[beginningAt++]))
{
targetWord = targetWord + fromMessage[beginningAt-1];
}
return targetWord;

Answer 1

Since this is a C++ question, how about using modern C++, instead of using dressed-up C code? The modern C++ library has all the algorithms and functions needed to implement all of this work for you:
#include <algorithm>
#include <cctype>
std::string paragraph;
// Somehow, figure out how to get your paragraph into this std::string, then:
auto b=paragraph.begin(), e=paragraph.end();
while (b != e)
{
// Find first alphanumeric character, using POSIX isalnum()
auto p=std::find_if(b, e, [](char c) { return isalnum(c); });
// Find the next non-alphanumeric chararacter
b=std::find_if(p, e, [](char c) { return !isalnum(c); });
if (isbadword(std::string(p, b)))
std::fill(p, b, '#');
}
This does pretty much what you asked, in a fraction of the size of all that manual code that manually searches this stuff. All you have to do is to figure out what...
bool isbadword(const std::string &s)
...needs to do.
Your homework assignment is how to slightly tweak this code to avoid, in certain specific situations, calling isbadword() with an empty string.