How can I detect the last iteration in a loop over std::map?

c++ stl iterator maps
cdleary picture cdleary · Sep 30, 2008 · Viewed 25k times · Source

I'm trying to figure out the best way to determine whether I'm in the last iteration of a loop over a map in order to do something like the following:

for (iter = someMap.begin(); iter != someMap.end(); ++iter) {
    bool last_iteration;
    // do something for all iterations
    if (!last_iteration) {
        // do something for all but the last iteration
    }
}

There seem to be several ways of doing this: random access iterators, the distance function, etc. What's the canonical method?

Edit: no random access iterators for maps!

Answer

Mark Ransom picture Mark Ransom · Sep 30, 2008

Canonical? I can't claim that, but I'd suggest 

final_iter = someMap.end();
--final_iter;
if (iter != final_iter) ...

Edited to correct as suggested by KTC. (Thanks! Sometimes you go too quick and mess up on the simplest things...)

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