How to loop through characters of a string in D language? (page 3)

On Friday, 10 December 2021 at 13:22:58 UTC, Matheus wrote: > My C way of thinking while using D: > > import std; > > string stripsemicolons(string input){ > char[] s = input.dup; > int j=0; > for(int i=0;i<input.length;++i){ > if(s[i] == ';'){ continue; } > s[j++] = s[i]; > } > s.length = j; > return s.idup; > } Oooh, finally someone suggested to preallocate storage for all these reinventions of the wheel :D I would suggest instead of the final idup checking the length and only duplicating if certain waste threshold is broken, otherwise just doing https://dlang.org/phobos/std_exception.html#assumeUnique (or a cast to string). The result is unique either way. Threshold could be relative for short strings and absolute for long ones. Makes little sense reallocating if you only waste a couple bytes, but makes perfect sense if you've just removed pages and pages of semicolons ;) Be interesting to see if this thread does evolve into a SIMD search...

On Friday, 10 December 2021 at 18:47:53 UTC, Stanislav Blinov wrote: > > Be interesting to see if this thread does evolve into a SIMD http://lemire.me/blog/2017/01/20/how-quickly-can-you-remove-spaces-from-a-string/

On Friday, 10 December 2021 at 12:15:18 UTC, Rumbu wrote: > > I thought it's a beauty contest. > Well, if it's a beauty contest, then i got a beauty.. char[("abc;def;ab".length - count("abc;def;ab", ";"))] b = "abc;def;ab".replace(";", "");

import std.stdio; char[] dontdothis(string s, int i=0, int skip=0){ if (s.length == i) return new char[](i - skip); if (s[i] == ';') return dontdothis(s, i+1, skip+1); auto r = dontdothis(s, i+1, skip); r[i-skip] = s[i]; return r; } int main() { string s = "abc;def;ab"; string s_new = cast(string)dontdothis(s); writeln(s_new); return 0; }

On Friday, 10 December 2021 at 22:35:58 UTC, Arjan wrote: > > "abc;def;ghi".tr(";", "", "d" ); > I don't think we have enough ways of doing the same thing yet... so here's one more.. "abc;def;ghi".substitute(";", "");

import std.stdio; string garbagefountain(string s){ if (s.length == 1) return s == ";" ? "" : s; return garbagefountain(s[0..$/2]) ~ garbagefountain(s[$/2..$]); } int main() { writeln(garbagefountain("abc;def;ab")); return 0; }

import std.stdio; @safe: string stripsemicolons(string s) @trusted { int i,n; foreach(c; s) n += c != ';'; // premature optimization auto r = new char[](n); foreach(c; s) if (c != ';') r[i++] = c; return cast(string)r; } int main() { writeln(stripsemicolons("abc;def;ab")); return 0; }

On Saturday, 11 December 2021 at 08:05:01 UTC, Ola Fosheim Grøstad wrote: > > Using libraries can trigger hidden allocations. ok. fine. no unnecessary, hidden allocations then. // ------------------ module test; import core.stdc.stdio : putchar; nothrow @nogc void main() { string str = "abc;def;ab"; ulong len = str.length; for (ulong i = 0; i < len; i++) { if (cast(int) str[i] != ';') putchar(cast(int) str[i]); } } // ------------------

December 11, 2021

Re: How to loop through characters of a string in D language?

Posted by Ola Fosheim Grøstad
in reply to forkit

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Ola Fosheim Grøstad

Posted in reply to forkit

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On Saturday, 11 December 2021 at 08:46:32 UTC, forkit wrote:

On Saturday, 11 December 2021 at 08:05:01 UTC, Ola Fosheim Grøstad wrote:

Using libraries can trigger hidden allocations.

ok. fine. no unnecessary, hidden allocations then.

// ------------------

module test;

import core.stdc.stdio : putchar;

nothrow @nogc void main()
{
string str = "abc;def;ab";

ulong len = str.length;

for (ulong i = 0; i < len; i++)
{
    if (cast(int) str[i] != ';')
        putchar(cast(int) str[i]);
}

}

// ------------------

putchar(…) is too slow!


@safe:

extern (C) long write(long, const void *, long);


void donttrythisathome(string s, char stripchar) @trusted {
	import core.stdc.stdlib;
    char* begin = cast(char*)alloca(s.length);
    char* end = begin;
    foreach(c; s) if (c != stripchar) *(end++) = c;
    write(0, begin, end - begin);
}


@system
void main() {
    string str = "abc;def;ab";
    donttrythisathome(str, ';');
}

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