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for(auto& entity : memoryManager.getItems()) entity->update(mFrameTime);
If memoryManager contains 1000 items, does memoryManager.getItems() get called 1000 times or only one at the beginning of the loop?
Does the compiler run any optimization with -O2 (or -O3)?
(memoryManager.getItems() returns a std::vector<Entity*>&)
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Remarks. Use the range-based for statement to construct loops that must execute through a range, which is defined as anything that you can iterate through—for example, std::vector , or any other C++ Standard Library sequence whose range is defined by a begin() and end() .
Range-for is as fast as possible since it caches the end iterator[citation provided], uses pre-increment and only dereferences the iterator once. Then, yes, range-for may be slightly faster, since it's also easier to write there's no reason not to use it (when appropriate).
Range-based for loop in C++ Range-based for loop in C++ is added since C++ 11. It executes a for loop over a range. Used as a more readable equivalent to the traditional for loop operating over a range of values, such as all elements in a container.
Range-based for loop in C++ Often the auto keyword is used to automatically identify the type of elements in range-expression. range-expression − any expression used to represent a sequence of elements. Also Sequence of elements in braces can be used.
It is only evaluated once. The standard defines a range-based for statement as equivalent to:
{
auto && __range = range-init;
for ( auto __begin = begin-expr, __end = end-expr; __begin != __end; ++__begin ) {
for-range-declaration = *__begin;
statement
}
}
where range-init is the expression (surrounded by parentheses) or braced-init-list after the :
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