The class boost::iostreams::zlib_compressor compresses data in the ZLIB format. In the example, compressed data is written and read again.īoost.IOStreams provides several data compression filters. This stream is used when you want to read data with filters. Thus, the example displays 5 and 0.Įxample 34.8 uses the stream boost::iostreams::filtering_istream in addition to boost::iostreams::filtering_ostream. It returns 0 if an incorrect filter type is passed as a template parameter.Įxample 34.7 writes five characters to the stream. component() returns a pointer to the filter. Because component() is a template, the type of the filter must be passed as a template parameter.

The index of the respective filter must be passed as a parameter.

This class provides the member functions characters() and lines().īoost::iostreams::filtering_stream provides the member function component() to access a filter. However, you can complete a stream if you add a device with push() after a call to pop().Įxample 34.7 uses the filter boost::iostreams::counter, which counts characters and lines. Please note that you must not use a stream that isn’t connected with a device. Without the call to pop(), boost::iostreams::regex_filter won’t process any data and won’t forward data to the device. Example 34.6 calls pop() after “ Boost” has been written to the stream. This happens when the device is removed from the stream with the member function pop(). That’s why boost::iostreams::regex_filter starts filtering only after a write operation is complete and all data is available. The filter boost::iostreams::regex_filter can’t process data character by character because regular expressions need to look at character groups. You can pass one or more filters, but once a device has been passed, the stream is complete, and you must not call push() again. The filter(s) must be passed before the device the order is important. This class provides a member function push(), which the filter and the device are passed to. The filter and the device are connected with the stream boost::iostreams::filtering_ostream. The filter will match one or more consecutive instances of the letter “ o” in “ Boost,” but not zero instances. The example replaces “ Boost” with “ C++”. The format string specifies what the characters should be replaced with. The regular expression describes what to replace. The filter expects a regular expression and a format string. The data is sent through a filter of type boost::iostreams::regex_filter, which replaces characters. Os.push(regex_filter) Įxample 34.6 uses the device boost::iostreams::array_sink to write data to an array.

C zlib example