Code Size Analysis

pw_string: Efficient, easy, and safe string manipulation

Save code space by replacing snprintf

The C standard library function snprintf is commonly used for string formatting. However, it isn’t optimized for embedded systems, and using it will bring in a lot of other standard library code that will inflate your binary size.

Size comparison: snprintf versus pw::StringBuilder

The fixed code size cost of pw::StringBuilder is smaller than that of std::snprintf. Using only pw::StringBuilder’s << and append methods instead of snprintf leads to significant code size reductions.

However, there are cases when the incremental code size cost of pw::StringBuilder is similar to that of snprintf. For example, each argument to pw::StringBuilder’s << method expands to a function call, but one or two pw::StringBuilder appends may still have a smaller code size impact than a single snprintf call. Using pw::StringBuilder error handling will also impact code size in a way that is comparable to snprintf.

Label	Segment	Delta
Total StringBuilder cost when used alongside snprintf	FLASH +44 [section .code] -2 _ctype_ +4 quorem +2 __mprec_tens +4 main +4 p05.0 NEW +698 __udivmoddi4 NEW +244 pw::string_internal::InitializeStringBuffer<>() NEW +220 pw::string::IntToString<>() NEW +168 pw::string::internal::kPowersOf10 NEW +74 pw::StringBuilder::append() NEW +60 pw::StringBuilder::ResizeAndTerminate() NEW +26 pw::StringBuilder::NullTerminate() NEW +20 pw::StringBuilder::HandleStatusWithSize() NEW +2 __aeabi_ldiv0	+1,568
StringBuilder cost when completely replacing snprintf	FLASH +55 [section .code] DEL -504 _svfprintf_r -3 _ctype_ +4 quorem -8 __mprec_tens DEL -184 __ssputs_r DEL -104 snprintf +4 main DEL -66 __wrap_realloc +2 pw::allocator::BucketBlockAllocator<>::ReserveBlock() -4 p05.0 DEL -8 __wrap__realloc_r NEW +698 __udivmoddi4 NEW +244 pw::string_internal::InitializeStringBuffer<>() NEW +220 pw::string::IntToString<>() NEW +168 pw::string::internal::kPowersOf10 NEW +74 pw::StringBuilder::append() NEW +60 pw::StringBuilder::ResizeAndTerminate() NEW +26 pw::StringBuilder::NullTerminate() NEW +20 pw::StringBuilder::HandleStatusWithSize() NEW +2 __aeabi_ldiv0	+696
Incremental cost relative to snprintf for 10 strings	FLASH -40 [section .code] -64 main +56 pw::StringBuilder::operator<< <>() NEW +8 pw::StringBuilder::push_back()	-40

Size comparison: snprintf versus pw::string::Format

The pw::string::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 pw::string::Format.

Label	Segment	Delta
Format instead of snprintf once, return size	FLASH -4 quorem DEL -104 snprintf -12 pw::string::OutputStringsToBuffer() NEW +88 _vsnprintf_r NEW +56 pw::string::FormatVaList() NEW +36 pw::string::Format() NEW +28 vsnprintf	+88
Format instead of snprintf 10 times, handle errors	FLASH +4 [section .code] -32 pw::string::OutputStringsToBuffer() DEL -104 snprintf DEL -44 (anonymous namespace)::ProcessResult() NEW +88 _vsnprintf_r NEW +56 pw::string::FormatVaList() NEW +36 pw::string::Format() NEW +28 vsnprintf	+32
Format instead of snprintf 50 times, no error handling	FLASH -8 pw::string::OutputStringsToBuffer() DEL -104 snprintf NEW +88 _vsnprintf_r NEW +56 pw::string::FormatVaList() NEW +36 pw::string::Format() NEW +28 vsnprintf	+96