CODEWITHSUNDEEP
c++io
Archr
Archr

Reputation: 1075

C++: getline freezes at end of file

I want to read in one file line-by-line and output each line I read to a new file. In this code, cin has been redirected to refer to the input file, and cout has been redirected to refer to the output file.

The loop successfully writes every line in the file, but then it gets stuck on the final getline call. As a result, "Done" is not written to the file and the program does not terminate.

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

int main() {

    string line;
    while(getline(cin, line)) {
        cout << line << endl;
    }

    cout << "Done";  

    return 0;
}

Strangely, if I forcibly terminate the program, it seems to suddenly execute as desired, with "Done" being written.

Can someone point me in the right direction? Is there a flaw in the code, or is this some external configuration issue?

Notes: The input file in question ends with a newline character. Also, I do not want to use any includes besides these two.

Upvotes: 4

Views: 1493

Answers (1)

Zalman Stern
Zalman Stern

Reputation: 3191

The code should terminate on end of file (EOF) or any sort of file error. (The getline being called is: http://en.cppreference.com/w/cpp/string/basic_string/getline It returns the cin istream and then invokes its boolean conversion operator: http://www.cplusplus.com/reference/ios/ios/operator_bool/ that checks if badbit or failbit is set on the stream. The failbit state should be set when a read is attempted with the stream already at EOF, or if there is an error.)

Per the comments above, it seems like this does work when the code is run from the shell directly. My guess is Eclipse is doing something complicated where it either intentionally sends the file into the program and then switches to an interactive input mode, or has a bug in which it doesn't close its end of a pipe or pty/tty it is using to send input to the program. (I.e. Eclipse is not binding stdin directly to the file itself in running the program.)

If one wanted to debug it further, one could look at the process state using tools like lsof. (Assuming a UNIXy system.) Might also be worth raising the issue in an Eclipse forum. The IDE is not my area of expertise.

Upvotes: 1

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