Re: A debug class has started

[forkit via Digitalmars-d-learn]

On Monday, 13 December 2021 at 20:28:26 UTC, H. S. Teoh wrote:
On Mon, Dec 13, 2021 at 08:04:24PM +0000, forkit via 
Digitalmars-d-learn wrote:
On Monday, 13 December 2021 at 12:06:53 UTC, WebFreak001 wrote:
> 
> You should really use `.dup` if you want to mutate your 
> string. (You would need to duplicate anyway if you don't 
> want an unsafe cast)

(this produces an unpredictable result??)
char* w = cast(char*)str.dup;

Shouldn't you be using:

        char* w = str.dup.ptr;

instead??


T

so here are all the possible options I've tried. only 2 of these 
actually produce the expected result.

// ------
module test;

import std : writeln, writefln;
import std.conv : to;

import core.stdc.string : strdup;
import std.string : toStringz;

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

    //char* w = cast(char*)str; // NOPE! A string constant is 
immutable, so expect undefined behaviour.

    char* w = strdup(cast(char*)str); // ok
    //char* w = cast(char*)str.toStringz; // also ok

    // all these below result in an extra character from 
'somewhere' appearing in the writeln output
    //char* w = cast(char*)str.dup; // nope
    //char* w = str.dup.ptr; // nope
    //char* w = &dup(cast(const(char)[])str)[0]; // nope

    writeln(replaceChar(w, str.length, ';', 'X'));
}

immutable(char)[] replaceChar(char* str, ulong len, char ch1, 
char ch2)
{
    for (ulong i = 0; i < len; i++)
    {
        if (str[i] == ch1)
        {
            writefln("Found %c at str[%d]", ch1, i); // fine
            str[i] = ch2;
        }
    }
    return to!(immutable(char)[])(str);
}
// ----------------