.. Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements. See the NOTICE file distributed with this work for additional information regarding copyright ownership. The ASF licenses this file to you under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License. .. include:: ../../common.defs .. default-domain:: cpp MemSpan ******* Synopsis ======== .. code-block:: cpp #include :class:`MemSpan` is a view on a contiguous section of writeable memory. A view does not own the memory and neither allocates nor de-allocates. The memory in the view is always owned by some other container and it is the responsibility of the code to make sure the lifetime of the view is no more than that of the owning container [#vector]_. Description =========== A :class:`MemSpan` is generally constructed on either an array or an allocated buffer. This allows the buffer to be passed around with intrinsic length information. The buffer can also be treated as an array of varying types, which makes working with serialized data much easier. Reference ========= .. class:: MemSpan A span of writable memory. Because this is a chunk of memory, conceptually delimited by start and end pointers, the sizing type is :code:`ptrdiff_t` so that all of the sizing is consistent with differences between pointers. The memory is owned by some other object and that object must maintain the memory as long as the span references it. .. function:: MemSpan(void * ptr, ptrdiff_t size) Construct a view starting at :arg:`ptr` for :arg:`size` bytes. .. function:: void * data() const Return a pointer to the first byte of the span. .. function:: ptrdiff_t size() const Return the size of the span. .. function:: bool operator == (MemSpan const& that) const Check the equality of two spans, which are equal if they contain the same number of bytes of the same values. .. function:: bool is_same(MemSpan const& that) const Check if :arg:`that` is the same span as :arg:`this`, that is the spans contain the exact same bytes. .. function:: template < typename V > V at(ptrdiff_t n) const Return a value of type :arg:`V` as if the span were are array of type :arg:`V`. .. function:: template < typename V > V * ptr(ptrdiff_t n) const Return a pointer to a value of type :arg:`V` as if the span were are array of type :arg:`V`. .. function:: MemSpan prefix(ptrdiff_t n) const Return a new instance that contains the first :arg:`n` bytes of the current span. If :arg:`n` is larger than the number of bytes in the span, only that many bytes are returned. .. function:: MemSpan& remove_prefix(ptrdiff_t n) Remove the first :arg:`n` bytes of the span. If :arg:`n` is more than the number of bytes in the span the result is an empty span. A reference to the instance is returned. .. rubric:: Footnotes .. [#vector] Strong caution must be used with containers such as :code:`std::vector` or :code:`std::string` because the lifetime of the memory can be much less than the lifetime of the container. In particular, adding or removing any element from a :code:`std::vector` can cause a re-allocation, invalidating any view of the original memory. In general views should be treated like iterators, suitable for passing to nested function calls but not for storing.