Iterating ranged-based for loop from end to begin [duplicate]

Question

Reverse iteration from last item to first item can be done like this:

for (int i = myContainer.size() - 1; i >= 0; --i) {
    // Do
}

How can I reverse a ranged-based for loop:

for (auto i : myContainer) {
    // Do
}

Thomas Sablik · Accepted Answer · 2019-06-17 06:34:26Z

0

std::reverse(std::begin(myContainer), std::end(myContainer));
for (auto i : myContainer) {
    // Do
}

This will add O(n) iterator swaps

answered Jun 17, 2019 at 6:24

Thomas Sablik

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10 Comments

Thanks. Is using std::reverse computationally more expensive than the traditional for (int i = myContainer.size() - 1; i >= 0; --i) method?

Yes, O(n) iterator swaps are added

Right. I think I might stick to the traditional for (int i = myContainer.size() - 1; i >= 0; --i) to avoid the added expense of std::reverse.

Sorry but this is a bad solution. No one would modify the whole container just to iterate it backwards.

@paceholder This is a correct answer to the question. You are free to provide a better answer.

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