In C++, is std::end guaranteed to be O(1) for all container types? [duplicate]

Question

If a container is likely to contain a large number of items, from a performance perspective, should one write

for (auto p = std::begin(container); p != std::end(container); ++p) {...}

or should one access the container's end outside the loop

const auto& theEnd = std::end(container);
for (auto p = std::begin(container); p != theEnd; ++p) {...}

I just wonder if std::end is O(1) for containers like sets and lists as well as vectors.

Answer 1

Yes, the complexity for end() is constant for all containers. The table "Container requirements" in C++ Standard 23.2.1 says so:

a.end() constant

Answer 2

According to container requirements described in Table 96 of the C++ Standard function end() has constant complexity.