4 ms·
If you are using an RTOS (which many timing-critical applications run on), you should be worried about memory allocations happening under the hood. If you don'
by gibsjose 11y ago
If you are using an RTOS (which many timing-critical applications run on), you should be worried about memory allocations happening under the hood.
If you don't have full control over when memory is being allocated/reallocated, your system is now non-deterministic.
With pure C, you can know exactly when those few extra instructions for resizing your dynamic array are going to happen.
- catnaroek 11y agoSame in C++. There's `std::vector::reserve`, which grows the vector's underlying physical buffer, without logically adding any new elements. If you `reserve` enough capacity before inserting anything, it's even a `O(1)` operation.
- gibsjose 11y agoVector and possibly string have that. The vast majority of STL structures do not.
- catnaroek 11y agoAll containers from the C++ standard library (please don't call it STL, that's Stepanov's original library) can be parameterized by an allocator. You can use whatever allocation policy you like best. However, most people use the default allocator because it's good enough. In any case, while C++ has lots of defects, “loss of control relative to what C gives you” isn't one of them.
- gibsjose 11y agoYeah, that's true.
- optforfon 11y ago(a bit of topic - but I'm humbly trying to learn more...) I've got zero experience writing allocators. Is there some common ones you use provided somewhere? Do you write your own? (in which case can you point me to where to learn to do that properly)
- catnaroek 11y agoI don't write allocators myself, but Boost has a pool allocator library [http://www.boost.org/doc/libs/1_60_0/libs/pool/doc/html/index.html http://www.boost.org/doc/libs/1_60_0/libs/pool/doc/html/inde...], which conforms to the Allocator concept defined in the standard library [http://en.cppreference.com/w/cpp/concept/Allocator http://en.cppreference.com/w/cpp/concept/Allocator].
- optforfon 11y agoThank you