Mysterious Error: Can You See Why?

[sysprog]

Reading the file iteratively (read a part, do something with it, then read the next part) is different from reading the whole file into memory before doing anything with any part of it. As @Mark44 pointed out, you can't do that with a very large file $-$ please look at the Hubbard C++ data structures book that you recently purchased $-$ it has many coding examples and explanations. I think that your reading of some it may help to further inform you for your interpretation of the Gaddis book code.