Read contents of a text file character by character into a vector without skipping whitespace or new lines

Question

So I have several text files. I need to figure out the 10 most common characters and words in the file. I've decided to use a vector, and load it with each character from the file. However, it needs to include white space and new lines.

This is my current function

void readText(ifstream& in1, vector<char> & list, int & spaces, int & words)
{
//Fills the list vector with each individual character from the text ifle
in1.open("test1");

in1.seekg(0, ios::beg);
std::streampos fileSize = in1.tellg();
list.resize(fileSize);

    string temp;
    char ch;
    while (in1.get(ch))
    {
        //calculates words
        switch(ch)
        {
        case ' ':
            spaces++;
            words++;
            break;
        default:
            break;  
        }
        list.push_back(ch);
    }
    in1.close();
}

But for some reason, it doesn't seem to properly hold all of the characters. I have another vector elsewhere in the program that has 256 ints all set to 0. It goes through the vector with the text in it and tallys up the characters with their 0-256 int value in the other vector. However, it's tallying them up fine but spaces and newlines are causing problems. Is there a more efficient way of doing this?

πάντα ῥεῖ · Answer 1 · 2016-09-20T21:00:37.407

4

The problem with your code right now is that you're calling

list.resize(fileSize);

and use

list.push_back(ch);

in your read loop at the same time. You only need one or the other.

Omit one of them.

Is there a more efficient way of doing this?

The easiest way is to resize the std::vector <char> with the size you already know and use std::ifstream::read() to read in the whole file in one go. Calculate everything everything else from the vector contents afterwards.
Something along these lines:

list.resize(fileSize);
in1.read(&list[0],fileSize);

for(auto ch : list) {
    switch(ch) {
       // Process the characters ...
    }
}

edited Sep 20 '16 at 21:00

answered Sep 20 '16 at 20:17

πάντα ῥεῖ

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Can std::ifstream::read() push characters directly into a vector? Or does it need a buffer as intermediary? – blackpen Sep 20 '16 at 20:41
1

@blackpen It uses the formerly resized vector as the buffer. Nothing to do with `push_back()`. – πάντα ῥεῖ Sep 20 '16 at 20:43
Thank you. How exactly do I use read to send a file to a vector? I also need to be able to use multiple files of random sizes – Sep 20 '16 at 20:43
@ConnorSchwinghammer I hope its clearer now.. You can always refer to the [reference documentation](http://en.cppreference.com/w/cpp/io/basic_istream/read) in 1st place though. – πάντα ῥεῖ Sep 20 '16 at 20:57
@πάνταῥεῖ, Good point! I didn't know what. Also, it seems in c++11 you could also do **list.data()** – blackpen Sep 20 '16 at 21:00
@blackpen No need to resort to `std::vector::data()`. – πάντα ῥεῖ Sep 20 '16 at 21:01
@πάνταῥεῖ, Does list.data() doesn't work here? Or does it have any disadvantages? I was just reading off from this [post](http://stackoverflow.com/a/6485519/3196458) – blackpen Sep 20 '16 at 21:11
@blackpen It would work fine, but I don't see any advantage of using it (its even more to type). – πάντα ῥεῖ Sep 20 '16 at 21:14
@πάνταῥεῖ, Agreed. – blackpen Sep 20 '16 at 21:19

Read contents of a text file character by character into a vector without skipping whitespace or new lines

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