chain
Chains are used by filtering streams and stream buffers to manage their underlying sequence of Filters and Devices. A chain represents a sequence of zero or more Filters with an optional Device at the end. If a chain contains a Device, it is considered complete and can be used to perform i/o. When a chain is used for output, data passes through the first filter in the chain, then through the second filter, and so on, and eventually reaches the Device at the end of the chain. When a chain is used for input, data travels in the opposite direction, beginning at the Device at the end of the chain, then passing through the filters in reverse order. By default, if the Device at the end of a chain is popped or if a chain is complete when it is destroyed, all the filters and devices in the chain are closed using the function close. This behavior can be modified using the member function set_auto_close.
The class template chain is parameterized by a mode. All the Filters and Devices which constitute a chain must have modes which refine the mode of the chain. For example, the class chain<input> has mode input. All Filters pushed onto such a chain must at least be InputFilters. Any Device pushed onto such a chain must at least be a Source.
Chains are CopyConstructible and Assignable. A copy of a chain represents the same sequence of Filters and Devices as the original chain; the components are not copied.
<boost/iostreams/chain.hpp>namespace boost { namespace iostreams { template< typename Mode, typename Ch = char, typename Tr = std::char_traits<Ch>, typename Alloc = std::allocator<Ch> > class chain; template< typename Mode, typename Ch = wchar_t, typename Tr = std::char_traits<Ch>, typename Alloc = std::allocator<Ch> > class wchain; template< typename Mode, typename Ch = char, typename Tr = std::char_traits<Ch>, typename Alloc = std::allocator<Ch> > class chain : public implementation-defined stream type { public: typedef Ch char_type; typedef Tr traits_type; typedef Mode mode; typedef Alloc allocator_type; typedef implementation-defined size_type; chain(); chain(const chain&); std::streamsize read(char_type* s, std::streamsize n); std::streamsize write(const char_type* s, std::streamsize n); stream_offset seek(stream_offset off, std::ios_base::seekdir way); const std::type_info& component_type(int n) const; template<typename T> T* component(int n) const; template<typename T> void push( const T& t, std::streamsize buffer_size = default value, std::streamsize pback_size = default value ); template<typename StreamOrStreambuf> void push( StreamOrStreambuf& t, std::streamsize buffer_size = default value, std::streamsize pback_size = default value ); void pop(); bool empty() const; size_type size() const; void reset(); bool is_complete() const; bool auto_close() const; void set_auto_close(bool close); bool sync(); bool strict_sync(); // Deprecated members template<int N> const std::type_info& component_type() const; template<int N, typename T> T* component() const; }; } } // End namespace boost::io
chain| Mode | - | A mode tag. |
| Ch | - | The character type |
| Tr | - | The traits type |
| Alloc | - | A standard library allocator type ([ISO], 20.1.5), used to allocate character buffers |
chain::chainchain();
Constructs a chain with an empty chain of Filters and Devices.
chain::chain chain(const chain& rhs);
Constructs a chain representing the same sequence of Filters and Devices as the given chain.
chain::readstd::streamsize read(char_type* s, std::streamsize n);
Invokes read on the first filter or device in this chain, which must be non-empty.
chain::write std::streamsize write(const char_type* s, std::streamsize n);
Invokes write on the first filter or device in this chain, which must be non-empty.
chain::seekstream_offset seek(stream_offset off, std::ios_base::seekdir way);
Invokes seek on the first filter or device in this chain, which must be non-empty.
chain::component_typeconst std::type_info& component_type(int n) const;
Returns a reference to an instance std::type_info corresponding to the type of the nth Filter or Device in this chain, which must have size at least n + 1. Components are numbered beginning at zero.
// Deprecated template<int N> const std::type_info& component_type() const;
Returns a reference to an instance std::type_info corresponding to the type of the Nth Filter or Device in this chain, which must have size at least N + 1. Components are numbered beginning at zero. The template argument N cannot be deduced, and must therefore be explicitly specified.
This member is deprecated; use the overload of component_type that takes an int argument instead.
chain::componenttemplate<typename T> T* component(int n) const;
Returns a pointer to the nth Filter or Device in this chain, if this chain has size at least n + 1 and the type of the nth Filter or Device is equal to T. Otherwise, returns a null pointer. The template argument T cannot be deduced, and must therefore be explicitly specified.
Users of Microsoft Visual Studio versions 6.0-7.0 must use the macro BOOST_IOSTREAMS_COMPONENT instead of this function.
// Deprecated template<int N, typename T> T* component() const;
Returns a pointer to the Nth Filter or Device in this chain, if this chain has size at least N + 1 and the type of the Nth Filter or Device is equal to T. Otherwise, returns a null pointer. The template arguments N and T cannot be deduced, and must therefore be explicitly specified.
This member is deprecated; use the overload of component that takes an int argument instead.
chain::pushtemplate<typename T> void push( const T& t, std::streamsize buffer_size, std::streamsize pback_size );
Appends a copy of t to this chain, which must not be complete. The parameters have the following interpretations:
| T | - | A CopyConstructible model of one of the Filter or Device concepts whose character type is Ch and whose mode refines Mode |
| t | - | An instance of T |
| buffer_size | - | The size of any buffers that need to be allocated |
| pback_size | - | The size of the putback buffer, relevant only if Mode is a refinement of input |
An instance of a Filter or Device type T which is not CopyConstructible may be appended to the chain in one of two ways:
T is a standard stream or stream buffer type, by using the templated overload of push taking a non-const reference.
If T is a Device, this chain will become complete upon the return of this function, and can then be used to perform i/o.
template<typename StreamOrStreambuffer> void push( StreamOrStreambuffer& t, std::streamsize buffer_size, std::streamsize pback_size );
Appends the given stream or stream buffer to this chain, which must not be complete. The parameters have the following interpretations:
| StreamOrStreambuffer | - | A standard stream or stream buffer type whose character type is Ch and whose mode refines Mode |
| buffer_size | - | The size of any buffers that need to be allocated |
| pback_size | - | The size of the putback buffer, relevant only if Mode is a refinement of input |
This chain will become complete upon the return of this function, and can then be used to perform i/o.
chain::pop void pop();
Removes the final Filter or Device from this chain, which must be non-empty. If this chain is complete, pop causes each Filter and Device in the chain to be closed using the function close, unless the auto-close feature has been disabled using set_auto_clos.
chain::emptybool empty() const;
Returns true if this chain contains no Filters or Devices.
chain::size size_type size() const;
Returns the number of Filters and Devices in this chain.
chain::reset void reset();
Clears this chain. If this chain is complete, reset causes each Filter and Device in the chain to be closed using the function close, regardless of whether the auto-close feature has been disabled using set_auto_close.
chain::is_completebool is_complete() const;
Returns true if this chain contains a Device. A chain is complete if and only if it is capable of performing i/o.
chain::auto_closebool auto_close() const;
Indicates whether the Filters and Devices in this chain will be closed automatically if pop is invoked while the chain is complete. Returns true unless the auto-close feature has been disabled using set_auto_close.
chain::set_auto_closevoid set_auto_close(bool close);
Specifies whether the Filters and Devices in this chain will be closed automatically if pop is invoked while the chain is complete. Does not prevent the Filters and Devices in this chain from being closed automatically if the chain is complete at destruction.
chain::sync bool sync();
Invokes the function flush on each Filter and Device in this chain, which must be complete. Returns true unless at least one of these components is Flushable and flush returns false when invoked on that component. A return value of true indicates that no error occurred, but does not guarantee that all buffered data has been successfully forwarded.
chain::strict_sync bool strict_sync();
Identical to sync except for the return value, which is false unless each Filter in this chain is Flushable and flush returns true when invoked on each component. A return value of true guarantees that all buffered data has been successfully forwarded.
wchaintemplate< typename Mode,
typename Ch = wchar_t,
typename Tr = std::char_traits<Ch>,
typename Alloc = std::allocator<Ch> >
class wchain;
Identical to chain, except for the default character type.
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© Copyright 2004-2007 Jonathan Turkanis
Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)