Hi all,
I've made a micro-benchmark to check how much the use of a character literal as
an argument of std::string::find outperforms the use of a single character
string literal:
#include
#include
#include
int main() {
int res = 0;
std::string s(STRING_LITERAL);
auto start = std::chrono::steady_clock::now();
for(int i = 0; i < 1000; i++) {
#ifdef CHAR_TEST
res += s.find('A');
#else
res += s.find("A");
#endif
}
auto end = std::chrono::steady_clock::now();
std::chrono::duration elapsed_seconds = end-start;
std::cout << "elapsed time: " << elapsed_seconds.count() << "s\n";
return res;
}
However, I have better performance with single character string literal when
the std::string contains a small string and my program is compiled with -O3:
> (echo "char with small string" ; clang++ -DSTRING_LITERAL=\"BAB\" -DCHAR_TEST
> -O3 -o bench_exe bench.cpp && ./bench_exe) ; (echo "string literal with small
> string" ; clang++ -DSTRING_LITERAL=\"BAB\" -O3 -o bench_exe bench.cpp &&
> ./bench_exe)
char with small string
elapsed time: 0.0551678s
string literal with small string
elapsed time: 0.0493302s
I'm using the 8.0.0 version of clang:
> clang++ --version
clang version 8.0.0
Target: x86_64-unknown-linux-gnu
Thread model: posix
I can reproduce this results on all of my run. On average, the use of a single
character string literal give me a 10% performance improvement.
My question is: is the use of a character literal as argument of
std::string::find always faster whatever the optimization level and the size of
the string?
Thanks.
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