Re: C tips (again)

[Denis Koroskin]

On Sun, 03 May 2009 14:19:08 +0400, bearophile <bearophileh...@lycos.com> wrote:

Denis Koroskin:

Mystring s = ...;
char c = s.data.ptr[42];

Thank you for your nice suggestion.

In Python newsgroups people usually before suggesting any solution try to run it to see if it works correctly (this isn't always possible).

The following program doesn't work to me when WITH_PTR is true (Error: Access Violation) (to be compiled with -release when WITH_PTR is false):

import std.c.stdio: printf;
import std.c.stdlib: malloc, exit;

const bool WITH_PTR = 1;

struct Mystring {
    int size;
    int capacity;
    char data[0];
}

void main() {
    string s = "hello, how are you?";

    int total_len = Mystring.sizeof + s.length + 1;
    auto str = cast(Mystring*)malloc(total_len);
    if (str is null) exit(-1);

    static if (WITH_PTR) {
        foreach (i, c; s)
            str.data.ptr[i] = c;
        str.data.ptr[s.length] = '\0';
        printf("%s\n", str.data.ptr);
    } else {
        foreach (i, c; s)
            str.data[i] = c;
        str.data[s.length] = '\0';
        printf("%s\n", &(str.data));
    }
}

Bye,
bearophile

I use that trick quite often and it works. The problem here is, DMD initialize 
0-length static arrays' ptr with null:

void main() {
   auto str = cast(Mystring*)malloc(42);
   assert(str.data.ptr !is null); // fails
}

I believe this issue needs to be posted to bugzilla.