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Copies bytes from a source buffer sequence to a target buffer sequence.
template< typename MutableBufferSequence, typename ConstBufferSequence> std::size_t buffer_copy( const MutableBufferSequence & target, const ConstBufferSequence & source);
A modifiable buffer sequence representing the memory regions to which the bytes will be copied.
A non-modifiable buffer sequence representing the memory regions from which the bytes will be copied.
The number of bytes copied.
The number of bytes copied is the lesser of:
buffer_size(target)
            buffer_size(source)
            
          This function is implemented in terms of memcpy,
          and consequently it cannot be used to copy between overlapping memory regions.