On Jul 5, 2022, at 1:29 AM, Dominique Pellé via Boost-users <boost-users@lists.boost.org> wrote:

Hi

This following program shows many allocations coming from boost::split(..., boost::is_any_of(",")): ``` $ cat split.cpp

#include <string> #include <cstdio> #include <boost/algorithm/string.hpp> #include <boost/container/small_vector.hpp>

int main() { std::string str = "foo,bar,foobar,quux"; std::size_t s = 0; for (int i = 0; i < 100; ++i) { boost::container::small_vector<std::string, 4> v; #ifdef USE_IS_ANY_OF boost::split(v, str, boost::is_any_of(",")); #else boost::split(v, str, [](const char c) { return c == ',';}); #endif s += v.size(); } fprintf(stderr, "%zu\n", s); } ``` When using boost::is_any_of(","), there are 7 dynamic allocations per loop iteration whereas when using the lambda predicate, there are 0 dynamic allocation per loop as shown below: ``` $ clang++ -std=c++14 -DUSE_IS_ANY_OF split.cpp $ heaptrack ./a.out ... allocations: 702

$ clang++ -std=c++14 split.cpp $ heaptrack ./a.out ... allocations: 2 ```

What happens if you change your code to create the `boost::is_any_of` object outside the loop? — Marshall