Count word frequency using map - c++

Question

This is my first time implementing map in C++. So given a character array with text, I want to count the frequency of each word occurring in the text. I decided to implement map to store the words and compare following words and increment a counter.
Following is the code I have written so far.
const char *kInputText = "\
So given a character array with text, I want to count the frequency of
each word occurring in the text.\n\
I decided to implement map to store the\n\
words and compare following words and increment a counter.\n";
typedef struct WordCounts
{
int wordcount;
}WordCounts;
typedef map<string, int> StoreMap;
//countWord function is to count the total number of words in the text.
void countWord( const char * text, WordCounts & outWordCounts )
{
outWordCounts.wordcount = 0;
size_t i;
if(isalpha(text[0]))
outWordCounts.wordcount++;
for(i=0;i<strlen(text);i++)
{
if((isalpha(text[i])) && (!isalpha(text[i-1])))
outWordCounts.wordcount++;
}
cout<<outWordCounts.wordcount;
}
//count_for_map() is to count the word frequency using map.
void count_for_map(const char *text, StoreMap & words)
{
string st;
while(text >> st)
words[st]++;
}
int main()
{
WordCounts wordCounts;
StoreMap w;
countWord( kInputText, wordCounts );
count_for_map(kInputText, w);
for(StoreMap::iterator p = w.begin();p != w.end();++p)
{
std::cout<<p->first<<"occurred" <<p->second<<"times. \n";
}
return 0;
}
Error: No match for 'operator >>' in 'text >> st'
I understand this is an operator overloading error, so I went ahead and
wrote the following lines of code.
//In the count_for_map()
/*istream & operator >> (istream & input,const char *text)
{
int i;
for(i=0;i<strlen(text);i++)
input >> text[i];
return input;
}*/
Am I implementing map in the wrong way?

Answer 1

There is no overload for >> with a const char* left hand side.
text is a const char*, not an istream, so your overload doesn't apply (and the overload 1: is wrong, and 2: already exists in the standard library).
You want to use the more suitable std::istringstream, like this:
std::istringstream textstream(text);
while(textstream >> st)
words[st]++;

Answer 2

If you use modern C++ language, then life will get by far easier.
First. Usage of a std::map is the correct approach.
This is a more or less standard approach for counting something in a container.
We can use an associative container like a std::map or a std::unordered_map. And here we associate a "key", in this case the "word" to count, with a value, in this case the count of the specific word.
And luckily the maps have a very nice index operator[]. This will look for the given key and if found, return a reference to the value. If not found, the it will create a new entry with the key and return a reference to the new entry. So, in bot cases, we will get a reference to the value used for counting. And then we can simply write:
std::unordered_map<std::string, unsigned int> counter{};
counter[word]++;
But how to get words from a string. A string is like a container containing elements. And in C++ many containers have iterators. And especially for strings there is a dedicated iterator that allows to iterate over patterns in a std::string. It is called std::sregex_token_iterator and described here.. The pattern is given as a std::regex which will give you a great flexibility.
And, because we have such a wonderful and dedicated iterator, we should use it!
Eveything glued together will give a very compact solution, with a minimal number of code lines.
Please see:
#include <iostream>
#include <string>
#include <regex>
#include <map>
#include <iomanip>
const std::regex re{ "\\w+" };
const std::string text{ R"(So given a character array with text, I want to count the frequency of
each word occurring in the text.
I decided to implement map to store the
words and compare following words and increment a counter.")" };
int main() {
std::map<std::string, unsigned int> counter{};
for (auto word{ std::sregex_token_iterator(text.begin(),text.end(),re) }; word != std::sregex_token_iterator(); ++word)
counter[*word]++;
for (const auto& [word, count] : counter)
std::cout << std::setw(20) << word << "\toccurred\t" << count << " times\n";
}