Spinning words in C++ and recieving error - c++

Question

I'm trying to create a program according to the prompt below but I keep recieving a Caught std::exception, what(): basic_string::at: __n (which is 0) >= this->size() (which is 0) error, I though I was solid at C++ but I guess time takes its toll. My code is down below. Basically, first I parse the string by space character and save them in a vector<string> after that I check if a word is larger than 5 and reverse it if it is and do nothing if it is not. If it isn't the final word, I add a space at the end. Bing bang boom, prompt complete, or at least I thought.
std::string spinWords(const std::string &str)
{
std::vector<std::string> words;
std::string spinnedWord;
int count = 0;
for(unsigned int i = 0; i < str.length(); i++)
{
char currentChar = str.at(i);
if (currentChar == ' ')
{
count++;
continue;
}
else if((int)words.size() == count)
{
words.push_back(&currentChar);
}
else
{
words[count] += currentChar;
}
}
for(unsigned int i = 0; i < words.size(); i++)
{
if(words[i].size() >= 5)
{
for (unsigned int j = words[i].length() - 1; j >= 0; j--)
{
spinnedWord += words[j].at(i);
}
}
if(i + 1 != words.size())
{
spinnedWord += ' ';
}
}
return spinnedWord;
}// spinWords
Write a function that takes in a string of one or more words, and
returns the same string, but with all five or more letter words
reversed (Just like the name of this Kata). Strings passed in will
consist of only letters and spaces. Spaces will be included only when
more than one word is present.
Edit1: I have changed words[j].at(i); to words[i].at(j);
and I have changed words.push_back(&currentChar); to words.push_back(std::string(1, currentChar));
From what I currently understand, when I was pushing back &currentChar, I was causing a undefined behavior. I'll look into how to avoid that in the future. However, the error from before is still present, so the question remains unanswered

Answer 1

for (unsigned int j = words[i].length() - 1; j >= 0; j--)
{
spinnedWord += words[j].at(i);
}
You swapped j an i here. It must be words[i].at(j). Also j probably shouldn't be unsigned here, because the loop condition j >= 0 is always true for unsigned integers.
EDIT: the UB concern for line words.push_back(&currentChar) is valid too. The way to fix it is to construct a string from a char explicitly:
words.push_back(std::string(1, currentChar));

Answer 2

words.push_back(&currentChar);
You're trying to construct a std::string from a pointer to a single character. This compiles because there is a matching constructor, but it takes a C-style string, which your pointer to a single character isn't.

Answer 3

Truly speaking I even do not understand your code. For example what the variable count is doing in the program. Or why you are using an additional container like std::vector when all can be and shall be done with an object of the type std::string because it has all resources to do the task.
The container std::vector is needed only if the assignment is to split a string into words and return the words in an object of the type std::vector<std::string>. But your task is entirely different.
Pay attention to that in general there can be more than one space between words. Even if it is not so in any case you shall use a general approach and not rely on that between words there is only one space.
Your function does not make sense for example when the original string starts from a space character. In this case count will be equal to 1 due to this if statement
if (currentChar == ' ')
{
count++;
continue;
}
but the size of the vector will be equal to 0, So as words.size() is not equal to count then the else statement will be executed
else if((int)words.size() == count)
{
words.push_back(&currentChar);
}
else
{
words[count] += currentChar;
}
that results in undefined behavior.
I can suggest the following solution. In the demonstrative program below I do not use the standard algorithm std::reverse because I think that you have to reverse a word by your own code.
Here you are.
#include <iostream>
#include <string>
#include <utility>
std::string spinWords( const std::string &s, std::string::size_type length = 5 )
{
std::string t( s );
const char *delim = " \t";
for ( std::string::size_type i = 0; i != t.size(); )
{
auto pos = t.find_first_not_of( delim, i );
if ( pos != std::string::npos )
{
i = t.find_first_of( delim, pos );
if ( i == std::string::npos ) i = t.size();
if ( length < i - pos )
{
auto n = i - pos;
for ( std::string::size_type j = 0; j < n / 2; j++ )
{
std::swap( t[pos + j], t[i - j - 1] );
}
}
}
else
{
i = t.size();
}
}
return t;
}
int main()
{
std::string s( "1 12 123 1234 12345 123456 1234567 123456789 1234567890" );
std::cout << s << '\n';
std::cout << spinWords( s ) << '\n';
return 0;
}
The program output is
1 12 123 1234 12345 123456 1234567 123456789 1234567890
1 12 123 1234 12345 654321 7654321 987654321 0987654321