How to construct a std::list iterator in loop with increment

Question

I'm trying to do a double-loop over a std::list to operate on each pair of elements. However, I'm having some trouble initialising the second iterator. The code I'd like to write is:

for(std::list<int>::iterator i = l.begin(); i != l.end(); ++i) {
    for(std::list<int>::iterator j = i+1; j != l.end(); ++j) {
        ...
    }
}

That doesn't work because list iterators aren't random-access, so you can't do +1. But I'm having some trouble finding a neat alternative; the compiler doesn't seem to be very happy with std::list<int>::iterator j(i)++; which I had some hope for. Achieving what I want seems like I'm going to have to have some awkward extra increment which won't fit the structure of the for loop nicely.

There are obvious alternatives (using a vector, for example!) but it seems to me that there should be some reasonably neat way of doing this which I'm just not seeing at the moment.

Thanks in advance for any help :)

Answer 1

for(std::list<int>::iterator i = l.begin(); i != l.end(); ++i) {
    std::list<int>::iterator j = i;
    for(std::advance(j, 1); j != l.end(); ++j) {
        ...
    }
}

Answer 2

How about:

for (std::list<int>::iterator i = l.begin(); i != l.end(); ++i) {
    for (std::list<int>::iterator j = i; ++j != l.end(); ) {
        // ...
    }
}