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 +60 [section .code] +4 quorem -4 main NEW +694 __udivmoddi4 NEW +242 pw::string::IntToString<>() NEW +204 pw::tokenizer::EncodeArgs() NEW +160 pw::string::internal::kPowersOf10 NEW +158 __aeabi_d2f NEW +80 pw::string_internal::InitializeStringBuffer<>() NEW +76 pw::StringBuilder::append() NEW +70 pw::StringBuilder::ResizeAndTerminate() NEW +68 pw::string::DecimalDigitCount() NEW +50 pw::StringBuilder::StringBuilder() NEW +48 pw::StringBuffer<>::StringBuffer() NEW +48 pw_varint_Encode64 NEW +44 pw::StringBuilder::operator<< <>() NEW +42 _pw_log_tokenized_EncodeTokenizedLog NEW +34 pw::span<>::subspan() NEW +32 pw::string::ClampedCString() NEW +32 pw::sys_io::WriteBytes() NEW +28 pw::tokenizer::EncodedMessage<>::EncodedMessage() NEW +28 pw_tokenizer_EncodeInt64() NEW +26 pw::string::internal::ClampedLength() NEW +24 pw::StringBuilder::NullTerminate() NEW +24 pw::StringBuilder::operator<<() NEW +20 pw::sys_io::WriteByte() NEW +20 pw_assert_HandleFailure NEW +18 pw::StringBuilder::HandleStatusWithSize() NEW +18 pw::span<>::operator[]() NEW +14 pw::StringBuffer<>::operator<< <>() NEW +8 pw_log_tokenized_HandleLog NEW +6 pw::ToString<>() NEW +4 __aeabi_idiv0 NEW +4 __aeabi_memmove	+2,384
StringBuilder cost when completely replacing snprintf	FLASH DEL -504 _svfprintf_r +56 [section .code] DEL -184 __ssputs_r DEL -104 snprintf DEL -92 _realloc_r -4 main DEL -16 _malloc_usable_size_r +4 p05.0 NEW +694 __udivmoddi4 NEW +242 pw::string::IntToString<>() NEW +204 pw::tokenizer::EncodeArgs() NEW +160 pw::string::internal::kPowersOf10 NEW +158 __aeabi_d2f NEW +80 pw::string_internal::InitializeStringBuffer<>() NEW +76 pw::StringBuilder::append() NEW +70 pw::StringBuilder::ResizeAndTerminate() NEW +68 pw::string::DecimalDigitCount() NEW +50 pw::StringBuilder::StringBuilder() NEW +48 pw::StringBuffer<>::StringBuffer() NEW +48 pw_varint_Encode64 NEW +44 pw::StringBuilder::operator<< <>() NEW +42 _pw_log_tokenized_EncodeTokenizedLog NEW +34 pw::span<>::subspan() NEW +32 pw::string::ClampedCString() NEW +32 pw::sys_io::WriteBytes() NEW +28 pw::tokenizer::EncodedMessage<>::EncodedMessage() NEW +28 pw_tokenizer_EncodeInt64() NEW +26 pw::string::internal::ClampedLength() NEW +24 pw::StringBuilder::NullTerminate() NEW +24 pw::StringBuilder::operator<<() NEW +20 pw::sys_io::WriteByte() NEW +20 pw_assert_HandleFailure NEW +18 pw::StringBuilder::HandleStatusWithSize() NEW +18 pw::span<>::operator[]() NEW +14 pw::StringBuffer<>::operator<< <>() NEW +8 pw_log_tokenized_HandleLog NEW +6 pw::ToString<>() NEW +4 __aeabi_idiv0 NEW +4 __aeabi_memmove	+1,480
Incremental cost relative to snprintf for 10 strings	FLASH -48 [section .code] -196 main -4 quorem +8 pw::string::IntToString<>() +46 pw::StringBuilder::operator<< <>() -12 OUTLINED_FUNCTION_0 +6 pw::ToString<>() NEW +24 pw::StringBuilder::operator<<()	-176

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 -24 pw::string::OutputStringsToBuffer() -2 pw::tokenizer::EncodedMessage<>::EncodedMessage() NEW +88 _vsnprintf_r NEW +52 pw::string::FormatVaList() NEW +28 vsnprintf NEW +22 pw::string::Format()	+56
Format instead of snprintf 10 times, handle errors	FLASH -68 pw::string::OutputStringsToBuffer() DEL -104 snprintf -2 pw::tokenizer::EncodedMessage<>::EncodedMessage() +2 OUTLINED_FUNCTION_2 DEL -10 OUTLINED_FUNCTION_4 NEW +88 _vsnprintf_r NEW +52 pw::string::FormatVaList() NEW +28 vsnprintf NEW +22 pw::string::Format()	+8
Format instead of snprintf 50 times, no error handling	FLASH -4 quorem DEL -104 snprintf -2 DefaultFaultHandler NEW +88 _vsnprintf_r NEW +52 pw::string::FormatVaList() NEW +28 vsnprintf NEW +22 pw::string::Format()	+80