C ++在带有数字的文本文件中读取

Question

I have a txt file with 16 lines of integers. Each line contains 5 integers, here are the first 4 lines of the file,

0 0 0 0 0

1 2 3 4 5

5 4 3 2 1

5 100 1000 10000 10500

I need to read one line at a time, store all 5 ints in an array, then find the max value. I can do this on my own just fine. What I am having trouble with is going to the next line in the file after I finish reading the previous line.

1. Read first line from text file

2. store numbers in an array

3. send array to a function that returns the largest integer in the array

4. place that returned number in a new array that will eventually contain the largest numbers from all 16 lines of the file

5. read the next line of the file

6. write the array with the 16 int array to a file

I am having trouble with step 5. Each time I run my code, it reads line 1 every time.

#include <iostream>
#include <fstream>
using namespace std;

int main()
{
    int n,i,j;
    int temp[5];
    //ask user
    cout<<"How many lines are in the file\n";
    cin>>n;
    int *array = new int[n];
    //open file
    ifstream inFile;
    inFile.open("input.txt");

    for(j=0;j<n;++j)
    {
        for(i=0;i<5;++i)
        {
            inFile >> temp[i];
            cout<<temp[i]<<" ";
        }
        cout<<"\n";
    }
    return 0;
}

As you can see, I don't have the find max value function yet, I want to fix how I am reading the file before I move on to analyzing the actual data.

And yes this is a homework project, due in a few days, but my teacher did not even explain reading in files and told us to read the explanation in the textbook (which didn't help for what we were doing). I am looking to learn not just pass the homework, so a brief explanation/example of what I'm missing is fine.

Answer 1

I would grab the entire line at once using using istream::getline() and then parse the resultant string. Then call getline() again, etc. As it is you're probably not reading in the endline character although why you're getting the exact behavior you are isn't quite clear to me.

Answer 2

Your code works fine for me. I believe there is a problem with opening a file, so it keeps outputting the temp[] elements as they were initialized. Try to get the inFile state while reading.

Answer 3

Well, I don't think you need an array. Just read in line by line, tokenize it, static cast each to int (look at ascii values within the number range 0-9 for beingextra cautious, check for negatives etc.) and directly store the max. Repeat till EOF and you would possibly have the most efficient solution.

So the steps would be

1) Declare a temporary string.

2) Read in a line

3) Tokenize on the space

4) Assume the first is the max. Continue reading and comparing. Swap the values if you find a larger one

5) Repeat till the end