Question

2012/11/13 Update:
I found my question had already been asked.
Here is a good solution for handling different line ending text files:
Getting std :: ifstream to handle LF, CR, and CRLF?

Is it possible to contribute to libstdc++? How?

---

2012/11/11

I found there’s something wrong with cout.
If there are two strings returned from getline(),
the second string will overwrite the first one in the output.

This is sample code:

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

int main()
{
    //normal code
    cout << "Normal result:" << endl;
    string str1 = "hello";
    cout << str1;
    str1 = "123";
    cout << str1;

    cout << endl;

    //broken code
    cout << "Bug?" << endl;
    ifstream fin;
    fin.open("test.dat");

    string str;

    getline(fin, str);
    cout << str;

    getline(fin, str);
    cout << str;

    fin.close();
    return 0;
}

And here is the input file (test.dat):

hello
123

The output will be:

Normal result:
hello123
Bug?
123lo

I’m using ubuntu 12.10 64-bit,
and the version of compiler is
g++ (Ubuntu/Linaro 4.7.2-2ubuntu1) 4.7.2.
Any advice?
Is there anyone tell me where to file a bug?

Answer 1

More likely than a bug in libstdc++ (which can occur, as well as in gcc, but are rather rare these days), there is incorrect line termination in your input file – likely it is using the DOS/Windows CR+LF line endings, which – as getline() discards the LF – results in the second string written over the first one. You can easily see this, if you run output of your program through some kind of hex-dumper, e.g. xxd.

Either check for \r at the end of the strings you read (btw, MacOS to version 9 used just this as the EOL marker), fix your input, or duly add new-lines to output, when printing.