Inspired by this question, asking how to append a vector to itself, my first thought was the following (and yes, I realize insert is a better option now):
#include <algorithm>
#include <iostream>
#include <iterator>
#include <vector>
int main() {
std::vector<int> vec {1, 2, 3};
std::copy (std::begin (vec), std::end (vec), std::back_inserter (vec));
for (const auto &v : vec)
std::cout << v << ' ';
}
However, this prints:
1 2 3 1 * 3
The * is a different number every time the program is run. The fact that it's only the 2 being replaced is peculiar, and if there actually is an explanation for that, I'd be interested to hear it. Continuing, if I append to a different vector (a copy of the original), it outputs correctly. It also outputs correctly if I add the following line before the copy one:
vec.reserve (2 * vec.size());
I was under the impression std::back_inserter was a safe way to add elements onto the end of a container, despite not reserving memory beforehand. If my understanding is correct, what's wrong with the copying line?
I assume it's nothing to do with the compiler, but I'm using GCC 4.7.1.