case statement ranges...

[John Ratliff]

Are case statement ranges standard C++ or a compiler extension?

ex:

switch (somevar) {
case 0 ... 9: method1(); break;
case 0xA: ... 0x23: method2(); break;
}

I thought they were standard, but I remember reading somewhere this was
a GNU extension. I want to remove them from my code if they are
non-standard.

Thanks,

--John Ratliff

[Victor Bazarov]

John Ratliff wrote:

Are case statement ranges standard C++ or a compiler extension?

They are not standard.

ex:

switch (somevar) {
case 0 ... 9: method1(); break;
case 0xA: ... 0x23: method2(); break;
}

I thought they were standard, but I remember reading somewhere this
was a GNU extension. I want to remove them from my code if they are
non-standard.

You can always make sure by switching to "strict" mode, IIRC.

V
--
Please remove capital 'A's when replying by e-mail
I do not respond to top-posted replies, please don't ask

[John Ratliff]

Victor Bazarov wrote:

John Ratliff wrote:

>Are case statement ranges standard C++ or a compiler extension?

They are not standard.

>ex:

switch (somevar) {
case 0 ... 9: method1(); break;
case 0xA: ... 0x23: method2(); break;
}

I thought they were standard, but I remember reading somewhere this
was a GNU extension. I want to remove them from my code if they are
non-standard.

You can always make sure by switching to "strict" mode, IIRC.

V

Thanks.

--John Ratliff

[Ivan Novick]

On Jan 29, 11:37 am, John Ratliff <[e-mail]:

Are case statement ranges standard C++ or a compiler extension?

ex:

switch (somevar) {
case 0 ... 9: method1(); break;
case 0xA: ... 0x23: method2(); break;

}I thought they were standard, but I remember reading somewhere this was
a GNU extension. I want to remove them from my code if they are
non-standard.

I would say they are non-standard, i have never seen them in the C++
standard document.

Ivan
http://www.0x4849.net

[Dave Rahardja]

On Mon, 29 Jan 2007 14:37:20 -0500, John Ratliff <us**@example.netwrote:

>Are case statement ranges standard C++ or a compiler extension?

ex:

switch (somevar) {
case 0 ... 9: method1(); break;
case 0xA: ... 0x23: method2(); break;
}

I thought they were standard, but I remember reading somewhere this was
a GNU extension. I want to remove them from my code if they are
non-standard.

Non-standard. Replace them with:

if (somevar >= 0 && somevar <= 9) { method1(); }
else if (somevar >= 0xa && somevar <= 0x23) { method2(); }

-dr

[Marcus Kwok]

Dave Rahardja <as*@me.comwrote:

On Mon, 29 Jan 2007 14:37:20 -0500, John Ratliff <us**@example.netwrote:

>>Are case statement ranges standard C++ or a compiler extension?

ex:

switch (somevar) {
case 0 ... 9: method1(); break;
case 0xA: ... 0x23: method2(); break;
}

Non-standard. Replace them with:

if (somevar >= 0 && somevar <= 9) { method1(); }
else if (somevar >= 0xa && somevar <= 0x23) { method2(); }

Or alternately, you can use the "fallthrough" behavior of the case
statements, depending on how much you wish to type:

switch (somevar) {
case 0:
case 1:
case 2:
/* you can fill in the rest here */
case 9:
method1();
break;

case 0xA:
/* ... */
case 0x23:
method2();
break;
}

--
Marcus Kwok
Replace 'invalid' with 'net' to reply

[Ivan Novick]

On Jan 30, 7:25 am, [e-mail] (Marcus Kwok) wrote:

Dave Rahardja <[e-mail]:

On Mon, 29 Jan 2007 14:37:20 -0500, John Ratliff <[e-mail]:

>Are case statement ranges standard C++ or a compiler extension?

>ex:

>switch (somevar) {
case 0 ... 9: method1(); break;
case 0xA: ... 0x23: method2(); break;
}

Non-standard. Replace them with:

if (somevar >= 0 && somevar <= 9) { method1(); }
else if (somevar >= 0xa && somevar <= 0x23) { method2(); }

Or alternately, you can use the "fallthrough" behavior of the case
statements, depending on how much you wish to type:

switch (somevar) {
case 0:
case 1:
case 2:
/* you can fill in the rest here */
case 9:
method1();
break;

case 0xA:
/* ... */
case 0x23:
method2();
break;
}

Umm, surely the generated machine code for this, must have to do more
comparisons if you have lots of cases than using ranges with greater
than and less than comparisons, hence this code should be slower.

Ivan
http://www.0x4849.net

[peter koch]

On Jan 30, 4:46 pm, "Ivan Novick" <[e-mail]:

On Jan 30, 7:25 am, [e-mail] (Marcus Kwok) wrote:

Dave Rahardja <[e-mail]:

On Mon, 29 Jan 2007 14:37:20 -0500, John Ratliff <[e-mail]:
>>Are case statement ranges standard C++ or a compiler extension?

>>ex:

>>switch (somevar) {
> case 0 ... 9: method1(); break;
> case 0xA: ... 0x23: method2(); break;
>>}

Non-standard. Replace them with:

if (somevar >= 0 && somevar <= 9) { method1(); }
else if (somevar >= 0xa && somevar <= 0x23) { method2(); }

Or alternately, you can use the "fallthrough" behavior of the case
statements, depending on how much you wish to type:

switch (somevar) {
case 0:
case 1:
case 2:
/* you can fill in the rest here */
case 9:
method1();
break;

case 0xA:
/* ... */
case 0x23:
method2();
break;
}

Umm, surely the generated machine code for this, must have to do more
comparisons if you have lots of cases than using ranges with greater
than and less than comparisons, hence this code should be slower.

No. When all cases are "dense", the compiler typically arranges the
code above to a jumptable - something like

if (somevar < 0 || somevar 0x23) goto L_done;
jump jump_table[somevar]

[peter koch]

On Jan 30, 4:46 pm, "Ivan Novick" <[e-mail]:

On Jan 30, 7:25 am, [e-mail] (Marcus Kwok) wrote:

Dave Rahardja <[e-mail]:

On Mon, 29 Jan 2007 14:37:20 -0500, John Ratliff <[e-mail]:
>>Are case statement ranges standard C++ or a compiler extension?

>>ex:

>>switch (somevar) {
> case 0 ... 9: method1(); break;
> case 0xA: ... 0x23: method2(); break;
>>}

Non-standard. Replace them with:

if (somevar >= 0 && somevar <= 9) { method1(); }
else if (somevar >= 0xa && somevar <= 0x23) { method2(); }

Or alternately, you can use the "fallthrough" behavior of the case
statements, depending on how much you wish to type:

switch (somevar) {
case 0:
case 1:
case 2:
/* you can fill in the rest here */
case 9:
method1();
break;

case 0xA:
/* ... */
case 0x23:
method2();
break;
}

Umm, surely the generated machine code for this, must have to do more
comparisons if you have lots of cases than using ranges with greater
than and less than comparisons, hence this code should be slower.

Nope. Typically the code gets faster as the compiler will use a jump-
table: indexing a vector with somevar gives an instruction pointer
which gets jumped to. The only comparisons would be against minimum
and maximun value. For the example something like:

if (somevar < 0 || somevar 0x23) goto L_done;
goto jump_table[somevar]; // obviously pseudo-code here

/Peter