filestream to vector, filesize wrong

I found many articles to this question, but none explained this in enough detail and I am still unexperienced with streams: I want to stream a file to a vector and this vector is already defined and contains some data.

This snippet seemed to work (it doesnt):

std::ifstream fileInputStream(path.wc_str(), std::ios::binary);
//byteVector contains some data and is of type: std::vector<unsigned char>*
byteVector->insert(byteVector->end(), 
  std::istream_iterator<unsigned char>(fileInputStream), 
  std::istream_iterator<unsigned char>());

In this article I found a method to get the length of my file: Using C++ filestreams (fstream), how can you determine the size of a file?

std::ifstream fileInputStream;
fileInputStream.open(path.wc_str(), std::ios::in | std::ios::binary);
fileInputStream.ignore(std::numeric_limits<std::streamsize>::max());
std::streamsize fileLength = fileInputStream.gcount();
fileInputStream.clear();   //  Since ignore will have set eof.
fileInputStream.seekg(0, std::ios_base::beg);

If I compare the vector->size from the first snippet and the fileLength from the second snippet, my vector is about 2KB short.

I want to avoid copying the data from one buffer to another, so if I need more buffers to read all data I'd prefer std::move or something similar. Someone has an idea whats wrong in my first snippet or how to accomplish this another way?

Should I read the file into another vector buffer and move that vector to the end of my first?