[Issue 6878] New: Mutable result for toStringz()

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=6878

           Summary: Mutable result for toStringz()
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: Phobos
        AssignedTo: nobody at puremagic.com
        ReportedBy: bearophile_hugs at eml.cc


--- Comment #0 from bearophile_hugs at eml.cc 2011-11-01 17:48:57 PDT ---
In some situations you have to call C functions that accept a char* (not
const). For simplify such usage cases I'd like std.string.toStringz to be
closer to this:


import core.stdc.string;

char* toStringz(immutable(char[]) s) pure nothrow
in
{
    // The assert below contradicts the unittests!
    //assert(memchr(s.ptr, 0, s.length) == null,
    //text(s.length, ": `", s, "'"));
}
out (result)
{
    if (result)
    {
        auto slen = s.length;
        while (slen > 0 && s[slen-1] == 0) --slen;
        assert(strlen(result) == slen);
        assert(memcmp(result, s.ptr, slen) == 0); // overkill?
    }
}
body
{
    /+ Unfortunately, this isn't reliable.
     We could make this work if string literals are put
     in read-only memory and we test if s[] is pointing into
     that.

     /* Peek past end of s[], if it's 0, no conversion necessary.
     * Note that the compiler will put a 0 past the end of static
     * strings, and the storage allocator will put a 0 past the end
     * of newly allocated char[]'s.
     */
     char* p = &s[0] + s.length;
     if (*p == 0)
     return s;
     +/

    // Need to make a copy
    auto copy = new char[s.length + 1];
    copy[0 .. s.length] = s[];
    copy[s.length] = '\0';

    return copy.ptr;
}

void main() {
    string t = "hello";
    char* s1 = toStringz(t);
    const(char*) s2 = toStringz(t);
    immutable(char*) s3 = toStringz(t);
    immutable(char)* s4 = toStringz(t);
}

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