Wrong output when parsing the file?

Question

I am using the following code to parse a file.

std::string line;
std::ifstream infile("C:\\t50_20_1.td");

int num;
int pred;
int succ;

while (std::getline(infile, line))
{
    std::istringstream iss(line);
    while(iss >> num || !iss.eof()) {
        if(iss.fail()) {
            iss.clear();
            continue;
        } else {
            std::cout<<num<<std::endl;
        }
    }
    std::cin.ignore();
}

I am trying to print all the numbers in the following file

50
1   35   11   3  13       10  5       11  2       19  1       21  10       23  2       26  3       29  6       35  5       42  10       44  5    
2   3   12   8  7       15  12       19  9       24  6       27  13       29  7       32  8       34  6       35  8       37  9       38  12       39  9    
3   19   7   4  15       8  2       10  7       15  12       21  11       26  9       36  10    
4   35   8   5  13       7  7       10  8       13  13       20  1       21  5       44  1       48  15

But when the program ends I only get one number as output

Step through your code with a debugger. And note you're flushing your stream twice in a row with `endl << flush`. — chris, Jul 06 '14 at 13:31
@LightnessRacesinOrbit It works well in [this context](http://ideone.com/BhVxSp). Was originally taken [from here](http://stackoverflow.com/a/24520662/1413395) — πάντα ῥεῖ, Jul 06 '14 at 13:35
@πάνταῥεῖ, That's not what the question's code does, though. If it fails a read, it just clears the flag and then tries to read what it just failed to read, over and over again. — chris, Jul 06 '14 at 13:40
@chris Of course, I know that. It was a misconception of the OP, and just a clarification from my side. I gave them the link to go figuring out how to read such kind of input. — πάντα ῥεῖ, Jul 06 '14 at 13:42
I test your code it works fine ! you are using `cin.ignore()` in while loop so you need to press enter for seeing other numbers ! — uchar, Jul 06 '14 at 13:44
I got the same outpout, then i pressed enter, and enter and I got the remaining numbers... — Christophe, Jul 06 '14 at 13:44
@Worker is it still the file where you try to read a well defined sequence of process numbers followed by a variable number of communication parameters ? — Christophe, Jul 06 '14 at 13:47
@xyz thanks. Write your answer in the answers section and thanks for your help. — zzzzz, Jul 06 '14 at 13:49
@Worker Also see [here please](http://ideone.com/X0Ozb3), I adapted your code a bit to simulate the file input, and it seems to work as expected for me. — πάντα ῥεῖ, Jul 06 '14 at 13:58

score 1 · Answer 1 · answered Jul 06 '14 at 15:53

I would recommend you remove the !iss.eof() conditional as it is not necessary in the while loop. The Enter key must be pressed to continue to parse the following lines. Please see the following code. Also, I recommend you add "using namespace std" which implies std:: where necessary and can make the code more readable. Lastly, a few of the variables you are declared are not actually used and so they have been removed from the code below.

#include <fstream>
#include <iostream>
#include <sstream>

using namespace std;

int main (int argc, char ** argv)
{
    string line = "";
    ifstream infile("C:\\t50_20_1.td");
    int num = 0;

    while (getline(infile, line))
    {
        istringstream iss(line);
        while(iss >> num) {
            if(iss.fail()) {
                iss.clear();
                continue;
            } else {
                cout << num << endl;
            }
        }
        std::cin.ignore();
    }
    return 0;
}

Sample Output (selected output only, all numbers are being outputted with the above code)

50
...
44
5
...
39
9
...
48
15

Wrong output when parsing the file?

1 Answers1