Wiring String ============= Small String Optimisation ------------------------- The :cpp:class:`String` class is probably the most used class in Arduino and Sming. Unfortunately it gets the blame for one of the most indidious problems in the embedded world, `heap fragmentation `__. To alleviate this problem, Sming uses a technique known as *Small String Optimisation*, which uses the available space inside the String object itself to avoid using the heap for small allocations of 10 characters or fewer. This was lifted from the `Arduino Esp8266 core `__. Superb work - thank you! Configuration Variables ----------------------- .. envvar:: STRING_OBJECT_SIZE minimum: 12 bytes (default) maximum: 128 bytes Must be an integer multiple of 4 bytes. This is an experimental feature which lets you increase the size of a String object to reduce heap allocations further. The effect of this will vary depending on your application, but you can see some example figures in :pull-request:`1951`. Benefits of increasing :envvar:`STRING_OBJECT_SIZE`: - Increase code speed - Fewer heap allocations Drawbacks: - Increased static memory usage for global/static String objects or embedded within global/static class instances. - A String can use SSO *or* the heap, but not both together, so in heap mode any additional SSO space will remain unused. Allows the size of a String object to be changed to increase the string length available before the heap is used. .. note:: The current implementation uses one byte for a NUL terminator, and another to store the length, so the maximum SSO string length is (STRING_OBJECT_SIZE - 2) characters. However, the implementation may change so if you need to check the maximum SSO string size in your code, please use ``String::SSO_CAPACITY``. API Documentation ----------------- .. doxygenclass:: String :members: .. doxygentypedef:: FlashString