digitalmars.D.learn - expected array behaviour

Mike James (10/10) Jan 01 2009 I have a function that uses 2 array strings defined similar to this...

John Reimer (4/19) Jan 01 2009 Wha?! If that's true, that looks like a nasty bug!

Mike James (36/36) Jan 01 2009 Hi John,

Mike James (3/3) Jan 01 2009 Forgot to mention - Windows XP.
Jarrett Billingsley (6/42) Jan 01 2009 If you want to modify the contents of string literals, like you're

John Reimer (3/11) Jan 01 2009 Oh, right. I missed that.

Jarrett Billingsley (5/10) Jan 01 2009 You'd get a runtime error if you were using Linux. For some reason

John Reimer (7/23) Jan 01 2009 Yes, that's one advantage to Linux. String literals aren't read-only on...

=?UTF-8?B?QW5kZXJzIEYgQmrDtnJrbHVuZA==?= (3/13) Jan 02 2009 The string literals are read-only on GDC for Win32 too, if that helps...

John Reimer (3/21) Jan 02 2009 That's interesting. So it's actually a compiler issue, not a platform o...

Mike James (6/6) Jan 01 2009 Got it - so I should do this...

Jarrett Billingsley (4/7) Jan 01 2009 Just "char[] array2 = array1.dup;"

Stewart Gordon (5/9) Jan 02 2009 Yes. Static arrays have value semantics, unlike dynamic arrays, which

Mike James <foo bar.com> writes:

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=-

Jan 01 2009

John Reimer <terminal.node gmail.com> writes:

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

Jan 01 2009

Mike James <foo bar.com> writes:

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=-

Jan 01 2009

Mike James <foo bar.com> writes:

Forgot to mention - Windows XP.

Regards,

-=mike=-

Jan 01 2009

"Jarrett Billingsley" <jarrett.billingsley gmail.com> writes:

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.

Jan 01 2009

John Reimer <terminal.node gmail.com> writes:

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

Jan 01 2009

"Jarrett Billingsley" <jarrett.billingsley gmail.com> writes:

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.

Jan 01 2009

John Reimer <terminal.node gmail.com> writes:

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

Jan 01 2009

=?UTF-8?B?QW5kZXJzIEYgQmrDtnJrbHVuZA==?= <afb algonet.se> writes:

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

Jan 02 2009

John Reimer <terminal.node gmail.com> writes:

Hello Anders,

 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
 


That's interesting.  So it's actually a compiler issue, not a platform one.

-JJR

Jan 02 2009

Mike James <foo bar.com> writes:

Got it - so I should do this...

const char[] array1= "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
char[]  array2 = new char[array1.length];

and then copy the contents of array1 into array2.

Regards,

-=mike=-

Jan 01 2009

"Jarrett Billingsley" <jarrett.billingsley gmail.com> writes:

On Thu, Jan 1, 2009 at 7:10 PM, Mike James <foo bar.com> wrote:
 Got it - so I should do this...

 const char[] array1= "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
 char[]  array2 = new char[array1.length];

Just "char[] array2 = array1.dup;"

.dup duplicates the array by creating a new array the same length and
copying the data over.

Jan 01 2009

Stewart Gordon <smjg_1998 yahoo.com> writes:

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.

Jan 02 2009

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digitalmars.D.learn - expected array behaviour