While not new line

Question

if i have a file like

1 5 6 9 7 1 
2 5 4 3 8 9
3 4 3 2 1 6
4 1 3 6 5 4

and i want to sort the numbers in every line .. how to know when there is a newline ? code for example :

while (!input.eof) {
    input>>num;
    while (not new line ?){
    input>>o;
    b.push_back(o);
    }
    sort (b.begin(),b.end());
    se=b.size();
    output<<num<<" "<<b[se-1]<<endl;
    b.clear();
}

Note: i tried while(input>>num) and getline will now work with me any ideas ?

If you want to read lines, your best bet is going to be `getline`. Note that [`while (!eof())` is wrong.](http://stackoverflow.com/questions/5605125/why-is-iostreameof-inside-a-loop-condition-considered-wrong) — chris, Jan 13 '14 at 01:22
Since it looks like you are iterating over every character individually, you might find it helpful to know that `"\n"` is the `CHAR` for a new line. — Alexander, Jan 13 '14 at 01:23
Why eof is wrong? Std::getline itself does move the file towards the end — Gasim, Jan 13 '14 at 01:25
@Gasim, click on the link that chris provided to see why `while (!eof())` is "wrong". More specifically, it's not a good way to check this kind of loop since one must attempt to read the EOF before `eof()` is true. It doesn't tell you if you are "at" the EOF. — lurker, Jan 13 '14 at 01:26

score 1 · Answer 1 · edited Jan 13 '14 at 01:35

1

You can use std::getline together with std::istringstream to read the file line by line, and then process each line individually:

#include <sstream>
std::string line;
while (std::getline(infile, line))
{
    std::istringstream iss(line);
    int a, b;
    //You can now read the numbers in the current line from iss
}

For further reference on how to read the file line by line, see this post.

edited Jan 13 '14 at 01:35

ApproachingDarknessFish

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answered Jan 13 '14 at 01:23

Uli Köhler

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score 1 · Answer 2 · answered Jan 13 '14 at 01:33

Your input doesn't work! Using a loop testing for stream.eof() as the only control for the input is always wrong. You always need to test your input after you tried to read it. Incidentally, I posted earlier how you can guarantee that there is no newline between to objects. there is already an answer using std::getline() as a first stage which is somewhat boring. Here is an alternate approach:

std::istream& noeol(std::istream& in) {
    for (int c; (c = in.peek()) != std::char_traits<char>::eof()
             && std::isspace(c); in.get()) {
        if (c == '\n') {
            in.setstate(std::ios_base::failbit);
        }
    }
    return in;
}

// ...

while (input >> num) {
    do {
        b.push_back(num);
    } while (input >> noeol >> num);
    std::sort (b.begin(),b.end());
    se=b.size();
    output<<num<<" "<<b[se-1]<<endl;
    b.clear();
    input.clear();
}

While not new line

2 Answers2