I have a function that uses 2 array strings defined similar to this...

const char[] array1 = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
char[]  array2 = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

If I make a change to a char in array1 it also changes the same in array2. But if I define the arrays as follows...

const char[26] array1 = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"; char[26]  array2 = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

It doesn't occur. Is this expected behaviour?

Regards,
-=mike=-

Hello Mike,

> I have a function that uses 2 array strings defined similar to this...
> 
> const char[] array1 = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"; char[]  array2 =
> "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
> 
> If I make a change to a char in array1 it also changes the same in
> array2. But if I define the arrays as follows...
> 
> const char[26] array1 = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"; char[26]  array2
> = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
> 
> It doesn't occur. Is this expected behaviour?
> 
> Regards,
> -=mike=-


Wha?!  If that's true, that looks like a nasty bug!

Is that dmd v2 or v1? Linux or Windows?

-JJR

On Thu, Jan 1, 2009 at 5:55 PM, Mike James <foo@bar.com> wrote:
> I have a function that uses 2 array strings defined similar to this...
>
> const char[] array1 = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
> char[]  array2 = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
>
> If I make a change to a char in array1 it also changes the same in array2. But if I define the arrays as follows...

You'd get a runtime error if you were using Linux.  For some reason string literals are not read-only, or Windows doesn't respect it, or something like that.  Modifying either array1 or array2 is technically illegal.  So, uh, don't do it.

Hi John,

I am using D1.038, dsss and Tango.

I've written a quick example but this one is even stranger...

========================================

module main;

import tango.io.Stdout;

int main() {
    func1();
    func2();

    return 0;
}

void func1() {
    char[] array1 = "ABCD";
    char[] array2 = "ABCD";

    Stdout(array1).newline;
    Stdout(array2).newline;
    Stdout.newline;

    array2[0] = 'Z';

    Stdout(array1).newline;
    Stdout(array2).newline;
    Stdout.newline;
}

void func2() {
    char[4] array1 = "ABCD";
    char[4] array2 = "ABCD";

    Stdout(array1).newline;
    Stdout(array2).newline;
    Stdout.newline;

    array2[1] = 'Q';

    Stdout(array1).newline;
    Stdout(array2).newline;
    Stdout.newline;
}

========================================

Regards,

-=mike=-

Forgot to mention - Windows XP.

Regards,

-=mike=-

On Thu, Jan 1, 2009 at 6:56 PM, Mike James <foo@bar.com> wrote:
> Hi John,
>
> I am using D1.038, dsss and Tango.
>
> I've written a quick example but this one is even stranger...
>
> ========================================
>
> module main;
>
> import tango.io.Stdout;
>
> int main() {
>    func1();
>    func2();
>
>    return 0;
> }
>
> void func1() {
>    char[] array1 = "ABCD";
>    char[] array2 = "ABCD";
>
>    Stdout(array1).newline;
>    Stdout(array2).newline;
>    Stdout.newline;
>
>    array2[0] = 'Z';
>
>    Stdout(array1).newline;
>    Stdout(array2).newline;
>    Stdout.newline;
> }
>
> void func2() {
>    char[4] array1 = "ABCD";
>    char[4] array2 = "ABCD";
>
>    Stdout(array1).newline;
>    Stdout(array2).newline;
>    Stdout.newline;
>
>    array2[1] = 'Q';
>
>    Stdout(array1).newline;
>    Stdout(array2).newline;
>    Stdout.newline;
> }
>
> ========================================
>
> Regards,
>
> -=mike=-
>

If you want to modify the contents of string literals, like you're doing here, put a .dup on them.

char[] array1 = "ABCD".dup;

Again, modifying the contents of string literals is illegal and the results are undefined.

Hello Jarrett,

> If you want to modify the contents of string literals, like you're
> doing here, put a .dup on them.
> 
> char[] array1 = "ABCD".dup;
> 
> Again, modifying the contents of string literals is illegal and the
> results are undefined.
> 


Oh, right.  I missed that.

-JJR

Hello Jarrett,

> On Thu, Jan 1, 2009 at 5:55 PM, Mike James <foo@bar.com> wrote:
> 
>> I have a function that uses 2 array strings defined similar to
>> this...
>> 
>> const char[] array1 = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"; char[]  array2 =
>> "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
>> 
>> If I make a change to a char in array1 it also changes the same in
>> array2. But if I define the arrays as follows...
>> 
> You'd get a runtime error if you were using Linux.  For some reason
> string literals are not read-only, or Windows doesn't respect it, or
> something like that.  Modifying either array1 or array2 is technically
> illegal.  So, uh, don't do it.
> 


Yes, that's one advantage to Linux.  String literals aren't read-only on Win32.  This is unfortunate because it means that these sort of bugs are significantly harder to diagnose on Windows than on Linux.  I remember that this was a bug in a early DUI version (now GtkD).  It's was pretty easy to spot on Linux because of the runtime error.

-JJR

John Reimer wrote:

>> You'd get a runtime error if you were using Linux.  For some reason
>> string literals are not read-only, or Windows doesn't respect it, or
>> something like that.  Modifying either array1 or array2 is technically
>> illegal.  So, uh, don't do it.
> 
> Yes, that's one advantage to Linux.  String literals aren't read-only on Win32.  This is unfortunate because it means that these sort of bugs are significantly harder to diagnose on Windows than on Linux.  I remember that this was a bug in a early DUI version (now GtkD).  It's was pretty easy to spot on Linux because of the runtime error.

The string literals are read-only on GDC for Win32 too, if that helps...

--anders

Mike James wrote:
<snip>
> const char[26] array1 = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
> char[26]  array2 = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
> 
> It doesn't occur. Is this expected behaviour?

Yes.  Static arrays have value semantics, unlike dynamic arrays, which have reference semantics.

Stewart.