blob: 37df397f94bd9eb6d2ed5dacfc4c61e0db9c1f9f [file] [log] [blame]
.. _chapter-pw-string:
.. default-domain:: cpp
.. highlight:: sh
String manipulation is a very common operation, but the standard C and C++
string libraries have drawbacks. The C++ functions are easy-to-use and powerful,
but require too much flash and memory for many embedded projects. The C string
functions are lighter weight, but can be difficult to use correctly. Mishandling
of null terminators or buffer sizes can result in serious bugs.
The ``pw_string`` module provides the flexibility, ease-of-use, and safety of
C++-style string manipulation, but with no dynamic memory allocation and a much
smaller binary size impact. Using ``pw_string`` in place of the standard C
functions eliminates issues related to buffer overflow or missing null
* ``pw_preprocessor``
* ``pw_status``
* ``pw_span``
The ``pw::string::Format`` and ``pw::string::FormatVaList`` functions provide
safer alternatives to ``std::snprintf`` and ``std::vsnprintf``. The snprintf
return value is awkward to interpret, and misinterpreting it can lead to serious
Size report: replacing snprintf with pw::string::Format
The ``Format`` functions have a small, fixed code size cost. However, relative
to equivalent ``std::snprintf`` calls, there is no incremental code size cost to
using ``Format``.
.. include:: format_size_report
StringBuilder facilitates building formatted strings in a fixed-size buffer. It
is designed to give the flexibility of ``std::string`` and
``std::ostringstream``, but with a small footprint. However, applications
sensitive to code size should use StringBuilder with care.
Size report: replacing snprintf with pw::StringBuilder
The fixed code size cost of StringBuilder is significant, though smaller than
``std::snprintf``. Using StringBuilder's << and append methods exclusively in
place of ``snprintf`` reduces code size, but ``snprintf`` may be difficult to
The incremental code size cost of StringBuilder is comparable to ``snprintf`` if
errors are handled. Each argument to StringBuilder's << expands to a function
call, but one or two StringBuilder appends may have a smaller code size impact
than a single ``snprintf`` call.
.. include:: string_builder_size_report
Future work
* StringBuilder's fixed size cost can be dramatically reduced by limiting
support for 64-bit integers.
* Consider integrating with the tokenizer module.