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 -8 main +4 vClearInterruptMaskFromISR NEW +266 pw::string::IntToString<>() NEW +160 pw::string::internal::kPowersOf10 NEW +92 pw::string_internal::InitializeStringBuffer<>() NEW +72 pw::string::DecimalDigitCount() NEW +38 pw::StringBuffer<>::StringBuffer() NEW +36 pw::StringBuilder::operator<< <>() NEW +28 pw::StringBuilder::operator<<() NEW +24 pw::StringBuilder::StringBuilder() NEW +14 pw::StringBuffer<>::operator<< <>() NEW +10 pw::ToString<>()	+736
StringBuilder cost when completely replacing snprintf	FLASH -4 [section .rodata] -4 main DEL -40 __wrap_snprintf +4 __bi_84 NEW +266 pw::string::IntToString<>() NEW +160 pw::string::internal::kPowersOf10 NEW +92 pw::string_internal::InitializeStringBuffer<>() NEW +72 pw::string::DecimalDigitCount() NEW +38 pw::StringBuffer<>::StringBuffer() NEW +36 pw::StringBuilder::operator<< <>() NEW +28 pw::StringBuilder::operator<<() NEW +24 pw::StringBuilder::StringBuilder() NEW +14 pw::StringBuffer<>::operator<< <>() NEW +10 pw::ToString<>()	+696
Incremental cost relative to snprintf for 10 strings	FLASH -48 [section .rodata] -160 main +14 pw::string::IntToString<>() +36 pw::StringBuilder::operator<< <>() +8 vClearInterruptMaskFromISR +10 pw::ToString<>() NEW +28 pw::StringBuilder::operator<<()	-112

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 -20 pw::string::OutputStringsToBuffer() -2 pw::string::FormatVaList() DEL -40 __wrap_snprintf NEW +22 pw::string::Format()	-40
Format instead of snprintf 10 times, handle errors	FLASH -88 pw::string::OutputStringsToBuffer() -2 pw::string::FormatVaList() DEL -40 __wrap_snprintf +4 vClearInterruptMaskFromISR NEW +22 pw::string::Format()	-104
Format instead of snprintf 50 times, no error handling	FLASH -2 pw::string::FormatVaList() DEL -40 __wrap_snprintf -4 vClearInterruptMaskFromISR NEW +22 pw::string::Format()	-24