code review 7888047: cmd/cgo: fix the cgo example on multiple assignment context.

cmd/cgo: fix the cgo example on multiple assignment context.

Change from atoi to strtol since atoi does not set errno.

[tebeka, 2013-03-21 16:05:51]

Hello golang-dev@googlegroups.com (cc: golang-dev@googlegroups.com,
minux.ma@gmail.com),

I'd like you to review this change to
https://code.google.com/p/go/

[minux1, 2013-03-21 16:39:18]

https://codereview.appspot.com/7888047/diff/5001/src/cmd/cgo/doc.go
File src/cmd/cgo/doc.go (right):

https://codereview.appspot.com/7888047/diff/5001/src/cmd/cgo/doc.go#newcode73
src/cmd/cgo/doc.go:73: n, err := C.strtol(C.CString("10"), nil, 50) // base too
large
do we need the comment here?

i now think we'd better use a simpler example here,
as C.CString() will malloc, but the example won't
have a way to free the memory thus creating a memory
leak -- we shouldn't recommend this usage.
so we'd better use a well-known C library function
that doesn't involve C strings.

how about this:
    f, err := C.sqrt(-1)

[tebeka, 2013-03-21 16:44:51]

On 2013/03/21 16:39:18, minux wrote:

> i now think we'd better use a simpler example here,
> as C.CString() will malloc, but the example won't
> have a way to free the memory thus creating a memory
> leak -- we shouldn't recommend this usage.
I agree.

> how about this:
>     f, err := C.sqrt(-1)
This is simpler, but then users need to do
    // #cgo LDFLAGS: -lm
which might be OK. Can't think of another example of the top of my head.

[minux1, 2013-03-21 17:05:54]

On Fri, Mar 22, 2013 at 12:44 AM,  <miki.tebeka@gmail.com> wrote:
> On 2013/03/21 16:39:18, minux wrote:
>> how about this:
>>      f, err := C.sqrt(-1)
> This is simpler, but then users need to do
>     // #cgo LDFLAGS: -lm
> which might be OK. Can't think of another example of the top of my head.
yes, making that example actually run require more efforts.
but i think that's ok, because the example is now simple and clear enough
that i imagine people won't need to actually run that example to understand.

anyone has better suggestions that don't rely on libm?

[rsc, 2013-03-21 20:13:38]

C.close(-1)

[minux1, 2013-03-21 20:22:42]

On Fri, Mar 22, 2013 at 4:13 AM, Russ Cox <rsc@golang.org> wrote:
> C.close(-1)
too Unixy? I'm afraid that people coming from Windows programming
background won't notice this is an error? (I'm not, so I'm only guessing
here)

I checked C99 standard, and found that the standard only mandates
these three errors in errno.h:
EDOM EILSEQ ERANGE

so it seems if we restrict ourselves to portable C99, we can only use
math.h functions.

[rsc, 2013-03-21 20:41:59]

Okay, C.sqrt(-1) it is.

[tebeka, 2013-03-22 01:55:39]

Hello golang-dev@googlegroups.com, minux.ma@gmail.com, rsc@golang.org (cc:
golang-dev@googlegroups.com),

Please take another look.

[bradfitz, 2013-03-22 03:05:58]

LGTM

On Thu, Mar 21, 2013 at 6:55 PM, <miki.tebeka@gmail.com> wrote:

> Hello golang-dev@googlegroups.com, minux.ma@gmail.com, rsc@golang.org
> (cc: golang-dev@googlegroups.com),
>
> Please take another look.
>
>
>
https://codereview.appspot.**com/7888047/<https://codereview.appspot.com/7888...
>
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[bradfitz, 2013-03-22 03:06:28]

*** Submitted as https://code.google.com/p/go/source/detail?r=cf22c93f26fa ***

cmd/cgo: fix the cgo example on multiple assignment context.

Change from atoi to strtol since atoi does not set errno.

R=golang-dev, minux.ma, rsc, bradfitz
CC=golang-dev
https://codereview.appspot.com/7888047

Committer: Brad Fitzpatrick <bradfitz@golang.org>