Fixed Length Containers

It makes sense to start with the simplest and most obvious addition to the standard in the FTL which are fixed length containers.

The FTL provides fixed length containers for the vector, queue, stack, bitset and array objects which allow developers to allocate all space for the container on the stack or within the allocation of another objects memory. By containing all required memory within the container itself the object will generally have more cache friendly memory access and gives developers much more control over the size of the. Within fixed containers no dynamic memory allocation takes place and a fatal warning is given if someone attempts to store values outside its scope.

There is no scope within the container for allocating or gracfully ignoring a request to add more data than the container can manage. If the container is full, this is a fatal error and the developer needs to know about this as soon as possible.

One notable omission from the fixed container set is a fixed deque. Due to the way memory is allocated for the deque (more on that in a future post), it would generally be more costly to provide a fixed amount of space for the deque when the library doesn’t know how the container will be ultimately used.

The fixed containers also provide null operations for functions like vector::reserve so a developer can swap between them at will without having to alter their code. This allows a dynamic version of the object to be used during development and then swapped to a fixed length container near the end of the project when the full range of the container is known and they are working on small optimisations.

To keep a consistent interface, the fixed array class is the implementation of the TR1 array specification and the array object outside the fixed namespace is based on an altered, dynamic implementation of that specification. The same goes for the bitset container.

Fixed length containers are declared by simply passing the size of the container along with the type.

ftl::fixed::fvector<int, 10> fixedVector;

You might be wondering why the fixed vector is called fvector rather than vector as it is within a separate name space. This is simply due to a bug in Doxygen which leads to the classes not being documented correctly. Since this is the tool we use for all documentation, this is a simple and easy work-around.

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