**C++
Write a function called count_words that takes a singleargument, a string filename .
-The function will open a file with the provided filename forreading.
– The goal of this function is to count the number of occurrencesof each word in the file (a text file)
– We will define a “word” as a sequence of characters separated bya whitespace
character.
– We will accomplish this using an unordered_map datastructure from the C++ standard
library (keyed by a string , storing an integer value).
– As we read a word in the file, we can count it’s occurrence inthe following way
// unordered_map keyed by string, and storing an
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