Speed comparison of passing and returning strings in C++

A simple benchmark that compares the speed of passing string to a method:

• as const std::string&
• as std::string
• as std::string_view
• as const std::string_view&
• as boost::string_view

Arguments are taken from:

• std::string
• boost::string_view
• const char*

Also, different return types are bechmarked:

• const std::string&
• std::string_view
• boost::string_view

for std::string and boost::string_view local types.

Results

Code was run on:

• Visual Studio 2022 (Version 17.8.3), x64 Release mode (my private machine)
• gcc 13.12 with -Ofast flag (https://godbolt.org/z/P3h3PTWYj)
• clang 17.0.1 with -Ofast flag (https://godbolt.org/z/66ddddKcd)

Typical timings are shown below.

Different parameter types

Visual Studio

Parameter type	Argument type	Time measured
const std::string&	std::string	0.0005871
std::string_view	std::string	0.0005866
const std::string_view&	std::string	0.0005869
boost::string_view	std::string	0.0005876
std::string	boost::string_view	0.0020685
const std::string&	const char*	0.002035
std::string	const char*	0.0020342
boost::string_view	const char*	0.0005944

gcc

Parameter type	Argument type	Time measured
const std::string&	std::string	0.000601113
std::string_view	std::string	0.000601281
const std::string_view&	std::string	0.000601274
boost::string_view	std::string	0.000601232
std::string	boost::string_view	0.00151555
const std::string&	const char*	0.00209719
std::string	const char*	0.00206175
boost::string_view	const char*	0.000600982

clang

Parameter type	Argument type	Time measured
const std::string&	std::string	0.000767679
std::string_view	std::string	0.00077255
const std::string_view&	std::string	0.000775012
boost::string_view	std::string	0.000765972
std::string	boost::string_view	0.000893587
const std::string&	const char*	0.00137083
std::string	const char*	0.00137587
boost::string_view	const char*	0.000767388

Different return types

Visual Studio

Return type	Local type	Time measured
const std::string&	std::string	0.0005700
std::string_view	std::string	0.0005697
boost::string_view	std::string	0.0005697
boost::string_view	boost::string_view	0.0005752
const boost::string_view&	boost::string_view	0.0005750

gcc

Return type	Local type	Time measured
const std::string&	std::string	0.00055094
std::string_view	std::string	0.000550952
boost::string_view	std::string	0.00055096
boost::string_view	boost::string_view	0.00055093
const boost::string_view&	boost::string_view	0.00055094

clang

Return type	Local type	Time measured
const std::string&	std::string	0.000560791
std::string_view	std::string	0.000559871
boost::string_view	std::string	0.00056079
boost::string_view	boost::string_view	0.000560781
const boost::string_view&	boost::string_view	0.000561132

Conclusion

Contrary to popular belief that for string_view parameter type argument is passed faster, relative differences in timings measured for different parameter and return value types are usually less then per mille except when constructor od std::string is invoked (corresponding values are bold in tables above).