Is on the stack, and so it goes out of scope before the asynchronous operationĬompletes. In the above example, the buffer is the std :: string When you call an asynchronous read or write you need to ensure that theīuffers for the operation are valid until the completion handler is called. clear () // invalidates iteratorsīoost.Asio takes advantage of this feature to add buffer debugging. Std :: vector v ( 1 ) std :: vector :: iterator i = v. If a program tries to use an iterator that has been invalidated, an assertion What this means is that the validity of iterators is checked at runtime. Microsoft Visual C 8.0 and later, provide a feature called iterator debugging. Some standard library implementations, such as the one that ships with data () std :: string line ( boost :: asio :: buffers_begin ( bufs ), boost :: asio :: buffers_begin ( bufs ) n ) Buffer std :: size_t n = boost :: asio :: read_until ( sock, sb, '\n' ) boost :: asio :: streambuf :: const_buffers_type bufs = sb. The buffers_iterator template parameter is automatically deduced.Īs an example, to read a single line from a socket and into a std :: string, you may write:īoost :: asio :: streambuf sb. Helperįunctions called buffers_begin() and buffers_end() are also provided, where types meeting MutableBufferSequence or ConstBufferSequence requirements) toīe traversed as though they were a contiguous sequence of bytes. Internal data beyond this limit will throw a std :: length_errorĬlass template allows buffer sequences (i.e. Any operation that would, if successful, grow the The streambuf constructor accepts a size_tĪrgument specifying the maximum of the sum of the sizes of the input sequenceĪnd output sequence. Of the input sequence by calling the commit()ĭata is removed from the front of the input sequence by calling the The return type of this function meets the MutableBufferSequence requirements.ĭata is transferred from the front of the output sequence to the back The output sequence of the streambuf is accessible via the prepare() The return type of this function meets the ConstBufferSequence requirements. The input sequence of the streambuf is accessible via the data() Such as the send or receive operations of a socket: Objects are internal to the streambuf object, but direct access to theĪrray elements is provided to permit them to be used with I/O operations, Sequence and output sequence with one or more objects of some characterĪrray type, whose elements store arbitrary values. The class boost :: asio :: basic_streambuf is derived from std :: basic_streambuf to associate the input The MutableBufferSequenceĬoncepts have been defined so that containers such as std :: vector, The library implementation to pass the raw memory to the underlyingįinally, multiple buffers can be passed to scatter-gather operations (suchīy putting the buffer objects into a container. In generalĪn application should never need to do this, but it is required by Type safety violations must be explicitly requested using the buffer_cast function. Or std :: vector of POD elements, or from a To provide further safety, the libraryĪlso includes mechanisms for automatically determining the size of Given a buffer instance,Ī user can only create another buffer representing the same range of There is protection against buffer overruns. That is, a mutable_buffer is convertible to Types behave as std::pair would in conversions. Of these is to provide an opaque representation of contiguous memory, where: However, Boost.Asio does not use the above definitions as-is, but instead Here, a mutable_buffer would be convertible to a const_buffer, but conversion Typedef std :: pair mutable_buffer typedef std :: pair const_buffer These two types could therefore be defined as follows: Memory (where the latter is created from the storage for a const-qualified Makes a distinction between modifiable memory (called mutable) and non-modifiable In addition to specifying buffers as a pointer and size in bytes, Boost.Asio May be passed to the scatter-gather operations. These can be stored in a container, which The approach used in Boost.Asio is to define a type (actually two types) Therefore we require an abstraction to represent a collection of buffers. A scatter-read receives data into multiple buffers.Ī gather-write transmits multiple buffers.
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