Re: Excessive dynamic allocation when using boost::split(..., > boost::is_any_of(", "))

From: Phil Endecott (spam_from_boost_users_at_[hidden])
Date: 2022-07-05 13:18:40

Hi Dominique,

Dominique Pelle wrote:
> This following program shows many allocations coming
> from boost::split(..., boost::is_any_of(",")):
> 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:

See this thread from 2008:

   https://lists.boost.org/Archives/boost//2008/02/133396.php

There are some benchmarks in my reply here:

   https://lists.boost.org/Archives/boost//2008/02/133415.php

I observed that C's strcspn was one of the better choices,
but it could be beaten for search sets known at compile time
with this:

template <char c0> bool is_any_of(char c) {
    return (c==c0);
}

template <char c0, char c1> bool is_any_of(char c) {
    return (c==c0) || is_any_of<c1>(c);
}

template <char c0, char c1, char c2> bool is_any_of(char c) {
    return (c==c0) || is_any_of<c1,c2>(c);
}

etc.

(Yes, I was writing that before variadic templates!)

I don't know if boost::is_any_of has changed in the 14 years
since then, but your observation suggests not.

Regards, Phil.