I have an input iterator CSVIterator as defined in this SO answer.

In my program, I now want to return such an iterator in a function and use it in my main(). The iterator is returned and I can access its contents. But when trying to iterate, I encounter a segmentation fault. Iterating within the returning function works.

I have two questions:

1. Why do I run into a seg fault? I thought about it being a problem of scope, but shouldn't then already the access to the iterator's contents lead to a segmentation fault?

2. How can my problem be fixed? The idea is to switch the opened files within a bigger loop at the correct iteration and always start at the beginning of that particular file. I come from a Python background and yielding one line of the file after the other feels natural to me, but maybe it's not recommended in C++?

Here's the code

// For the definition of CSVIterator, see
//
CSVIterator fileIter(int time)
{ std::string tstring = std::to_string(time); std::string ext = ".csv"; std::ifstream file(tstring + ext); CSVIterator iter(file); // This would work: // ++iter; return iter;
}
int main()
{ CSVIterator csvit; for (i=0; i<10000; i++) { if (i%20 == 0) { csvit = fileIter(i); } // I can access the iterator's contents // like (*csvit)[0] correctly. // However,iterating in here doesn't work. ++csvit; // seg fault here } return 0;
}

1 Answer

Yes, because file is a local variable. That means that you are iterating over something that has gone out of scope (when the function terminated), this provokes Undefined Behavior, which explains the crash.

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Notice how in the answer you linked, file is declared inside main().

1

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