Find Unique Characters in a File

Question

I have a file with 450,000+ rows of entries. Each entry is about 7 characters in length. What I want to know is the unique characters of this file.

For instance, if my f

Answer 1

in c++ i would first loop through the letters in the alphabet then run a strchr() on each with the file as a string. this will tell you if that letter exists, then just add it to the list.