[{"id":435,"web_url":"https://patchwork.libcamera.org/comment/435/","msgid":"<20190121092646.GC4420@pendragon.ideasonboard.com>","date":"2019-01-21T09:26:46","subject":"Re: [libcamera-devel] [PATCH] libcamera: v4l2_device: Return const\n\tstd::string","submitter":{"id":2,"url":"https://patchwork.libcamera.org/api/people/2/","name":"Laurent Pinchart","email":"laurent.pinchart@ideasonboard.com"},"content":"Hi Jacopo,\n\nOn Mon, Jan 21, 2019 at 10:20:20AM +0100, Jacopo Mondi wrote:\n> Make getter functions of V4L2Device return std::string as the rest of\n> the library does.\n\nThis is something that has been discussed during the review of Kieran's\noriginal patch I believe. The question was whether it would be more\nefficient to use const char * or a an std::string, and the answer to\nthat question depends on the expected usage of those methods. If all\nusers need an std::string, then I agree that the methods below can as\nwell construct one. On the other hand, if some users need a const char\n*, it is a bit pointless to convert from const char * to std::string and\nthen back to const char * using c_str(). This is why we have opted for\nconst char * here.\n\nThis is a generic question that we should ask ourselves through the\nlibrary. Anyone with free time to analyze the problem ? :-)\n\n> Signed-off-by: Jacopo Mondi \n> ---\n> src/libcamera/include/v4l2_device.h | 6 +++---\n> 1 file changed, 3 insertions(+), 3 deletions(-)\n> \n> diff --git a/src/libcamera/include/v4l2_device.h b/src/libcamera/include/v4l2_device.h\n> index 474c05b..5fe3d82 100644\n> --- a/src/libcamera/include/v4l2_device.h\n> +++ b/src/libcamera/include/v4l2_device.h\n> @@ -45,9 +45,9 @@ public:\n> \tbool isOpen() const;\n> \tvoid close();\n> \n> -\tconst char *driverName() const { return caps_.driver(); }\n> -\tconst char *deviceName() const { return caps_.card(); }\n> -\tconst char *busName() const { return caps_.bus_info(); }\n> +\tconst std::string driverName() const { return std::string(caps_.driver()); }\n> +\tconst std::string deviceName() const { return std::string(caps_.card()); }\n> +\tconst std::string busName() const { return std::string(caps_.bus_info()); }\n\nIf we wanted to return an std::string, we should drop the const as the\nstring is returned by value.\n\n> \n> private:\n> \tstd::string devnode_;","headers":{"Return-Path":"","Received":["from perceval.ideasonboard.com (perceval.ideasonboard.com\n\t[213.167.242.64])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTPS id 2314F60C65\n\tfor ;\n\tMon, 21 Jan 2019 10:26:47 +0100 (CET)","from pendragon.ideasonboard.com\n\t(dfj612yhrgyx302h3jwwy-3.rev.dnainternet.fi\n\t[IPv6:2001:14ba:21f5:5b00:ce28:277f:58d7:3ca4])\n\tby perceval.ideasonboard.com (Postfix) with ESMTPSA id 8E62F53E;\n\tMon, 21 Jan 2019 10:26:46 +0100 (CET)"],"DKIM-Signature":"v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com;\n\ts=mail; t=1548062806;\n\tbh=OCKaYxMdMn9hCZ1LLPa1VupOhyhvq4fZKi9YojSUavM=;\n\th=Date:From:To:Cc:Subject:References:In-Reply-To:From;\n\tb=Jd1WQ8SDj8EmEKsVnxeVI8h/0hlCth9u3REBoKXYjmpqR1OBS4oxYhQYCRl+1n9Ro\n\tvRvBuDYJBW/IzTH71L5RJ+27QxZCghzadpNxyxS8lCV0LrY7LUNTLlD93uzr6I7xr3\n\tNjoFyWjQx68JYD/fiE3MLKS5f6kA4n0LOWehy15U=","Date":"Mon, 21 Jan 2019 11:26:46 +0200","From":"Laurent Pinchart ","To":"Jacopo Mondi ","Cc":"libcamera-devel@lists.libcamera.org","Message-ID":"<20190121092646.GC4420@pendragon.ideasonboard.com>","References":"<20190121092020.4145-1-jacopo@jmondi.org>","MIME-Version":"1.0","Content-Type":"text/plain; charset=utf-8","Content-Disposition":"inline","In-Reply-To":"<20190121092020.4145-1-jacopo@jmondi.org>","User-Agent":"Mutt/1.10.1 (2018-07-13)","Subject":"Re: [libcamera-devel] [PATCH] libcamera: v4l2_device: Return const\n\tstd::string","X-BeenThere":"libcamera-devel@lists.libcamera.org","X-Mailman-Version":"2.1.23","Precedence":"list","List-Id":"","List-Unsubscribe":",\n\t","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n\t","X-List-Received-Date":"Mon, 21 Jan 2019 09:26:47 -0000"}},{"id":436,"web_url":"https://patchwork.libcamera.org/comment/436/","msgid":"<33ee9dea-f115-555b-8130-873fd8770c70@ideasonboard.com>","date":"2019-01-21T09:34:42","subject":"Re: [libcamera-devel] [PATCH] libcamera: v4l2_device: Return const\n\tstd::string","submitter":{"id":4,"url":"https://patchwork.libcamera.org/api/people/4/","name":"Kieran Bingham","email":"kieran.bingham@ideasonboard.com"},"content":"Hi Jacopo,\n\nOn 21/01/2019 09:26, Laurent Pinchart wrote:\n> Hi Jacopo,\n> \n> On Mon, Jan 21, 2019 at 10:20:20AM +0100, Jacopo Mondi wrote:\n>> Make getter functions of V4L2Device return std::string as the rest of\n>> the library does.\n>\n> This is something that has been discussed during the review of Kieran's\n> original patch I believe. The question was whether it would be more\n> efficient to use const char * or a an std::string, and the answer to\n> that question depends on the expected usage of those methods. If all\n> users need an std::string, then I agree that the methods below can as\n> well construct one. On the other hand, if some users need a const char\n> *, it is a bit pointless to convert from const char * to std::string and\n> then back to const char * using c_str(). This is why we have opted for\n> const char * here.\n\n\nAnd because the compiler can automatically convert from a const char *\nto a std::string using the string constructors ... so you can still use\nthese methods anywhere you would use a std::string...\n\n\n\n\n> This is a generic question that we should ask ourselves through the\n> library. Anyone with free time to analyze the problem ? :-)\n> \n>> Signed-off-by: Jacopo Mondi \n>> ---\n>> src/libcamera/include/v4l2_device.h | 6 +++---\n>> 1 file changed, 3 insertions(+), 3 deletions(-)\n>>\n>> diff --git a/src/libcamera/include/v4l2_device.h b/src/libcamera/include/v4l2_device.h\n>> index 474c05b..5fe3d82 100644\n>> --- a/src/libcamera/include/v4l2_device.h\n>> +++ b/src/libcamera/include/v4l2_device.h\n>> @@ -45,9 +45,9 @@ public:\n>> \tbool isOpen() const;\n>> \tvoid close();\n>>\n>> -\tconst char *driverName() const { return caps_.driver(); }\n>> -\tconst char *deviceName() const { return caps_.card(); }\n>> -\tconst char *busName() const { return caps_.bus_info(); }\n>> +\tconst std::string driverName() const { return std::string(caps_.driver()); }\n>> +\tconst std::string deviceName() const { return std::string(caps_.card()); }\n>> +\tconst std::string busName() const { return std::string(caps_.bus_info()); }\n> \n> If we wanted to return an std::string, we should drop the const as the\n> string is returned by value.\n> \n>>\n>> private:\n>> \tstd::string devnode_;\n>","headers":{"Return-Path":"","Received":["from perceval.ideasonboard.com (perceval.ideasonboard.com\n\t[IPv6:2001:4b98:dc2:55:216:3eff:fef7:d647])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTPS id 498D360C65\n\tfor ;\n\tMon, 21 Jan 2019 10:34:45 +0100 (CET)","from [192.168.0.21]\n\t(cpc89242-aztw30-2-0-cust488.18-1.cable.virginm.net [86.31.129.233])\n\tby perceval.ideasonboard.com (Postfix) with ESMTPSA id 7990653E;\n\tMon, 21 Jan 2019 10:34:44 +0100 (CET)"],"DKIM-Signature":"v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com;\n\ts=mail; t=1548063284;\n\tbh=WXwM2varxxKU5BMb65fdz4VnhXUr/jBIHYtDqhp9FGQ=;\n\th=Reply-To:Subject:To:Cc:References:From:Date:In-Reply-To:From;\n\tb=sZ5bg5RGlM1GIgiNJuEvZaIwNq7Nrfn3Dj9JRP+ROPiGXZ3PAodW4kqffB1xPZcfH\n\ttlXGRGP3dRbyJ7af7nOlvgKjHljIzBRm8MoSXThnwWLCG7qTgi4BWRInKJ5KCoKQj2\n\ti6TfEyw14GU4KIoHwM8X6KkOfuhR8Eyl/dLJNJjk=","Reply-To":"kieran.bingham@ideasonboard.com","To":"Laurent Pinchart ,\n\tJacopo Mondi ","Cc":"libcamera-devel@lists.libcamera.org","References":"<20190121092020.4145-1-jacopo@jmondi.org>\n\t<20190121092646.GC4420@pendragon.ideasonboard.com>","From":"Kieran Bingham ","Openpgp":"preference=signencrypt","Autocrypt":"addr=kieran.bingham@ideasonboard.com; keydata=\n\tmQINBFYE/WYBEACs1PwjMD9rgCu1hlIiUA1AXR4rv2v+BCLUq//vrX5S5bjzxKAryRf0uHat\n\tV/zwz6hiDrZuHUACDB7X8OaQcwhLaVlq6byfoBr25+hbZG7G3+5EUl9cQ7dQEdvNj6V6y/SC\n\trRanWfelwQThCHckbobWiQJfK9n7rYNcPMq9B8e9F020LFH7Kj6YmO95ewJGgLm+idg1Kb3C\n\tpotzWkXc1xmPzcQ1fvQMOfMwdS+4SNw4rY9f07Xb2K99rjMwZVDgESKIzhsDB5GY465sCsiQ\n\tcSAZRxqE49RTBq2+EQsbrQpIc8XiffAB8qexh5/QPzCmR4kJgCGeHIXBtgRj+nIkCJPZvZtf\n\tKr2EAbc6tgg6DkAEHJb+1okosV09+0+TXywYvtEop/WUOWQ+zo+Y/OBd+8Ptgt1pDRyOBzL8\n\tRXa8ZqRf0Mwg75D+dKntZeJHzPRJyrlfQokngAAs4PaFt6UfS+ypMAF37T6CeDArQC41V3ko\n\tlPn1yMsVD0p+6i3DPvA/GPIksDC4owjnzVX9kM8Zc5Cx+XoAN0w5Eqo4t6qEVbuettxx55gq\n\t8K8FieAjgjMSxngo/HST8TpFeqI5nVeq0/lqtBRQKumuIqDg+Bkr4L1V/PSB6XgQcOdhtd36\n\tOe9X9dXB8YSNt7VjOcO7BTmFn/Z8r92mSAfHXpb07YJWJosQOQARAQABtDBLaWVyYW4gQmlu\n\tZ2hhbSA8a2llcmFuLmJpbmdoYW1AaWRlYXNvbmJvYXJkLmNvbT6JAkAEEwEKACoCGwMFCwkI\n\tBwIGFQgJCgsCBBYCAwECHgECF4ACGQEFAlnDk/gFCQeA/YsACgkQoR5GchCkYf3X5w/9EaZ7\n\tcnUcT6dxjxrcmmMnfFPoQA1iQXr/MXQJBjFWfxRUWYzjvUJb2D/FpA8FY7y+vksoJP7pWDL7\n\tQTbksdwzagUEk7CU45iLWL/CZ/knYhj1I/+5LSLFmvZ/5Gf5xn2ZCsmg7C0MdW/GbJ8IjWA8\n\t/LKJSEYH8tefoiG6+9xSNp1p0Gesu3vhje/GdGX4wDsfAxx1rIYDYVoX4bDM+uBUQh7sQox/\n\tR1bS0AaVJzPNcjeC14MS226mQRUaUPc9250aj44WmDfcg44/kMsoLFEmQo2II9aOlxUDJ+x1\n\txohGbh9mgBoVawMO3RMBihcEjo/8ytW6v7xSF+xP4Oc+HOn7qebAkxhSWcRxQVaQYw3S9iZz\n\t2iA09AXAkbvPKuMSXi4uau5daXStfBnmOfalG0j+9Y6hOFjz5j0XzaoF6Pln0jisDtWltYhP\n\tX9LjFVhhLkTzPZB/xOeWGmsG4gv2V2ExbU3uAmb7t1VSD9+IO3Km4FtnYOKBWlxwEd8qOFpS\n\tjEqMXURKOiJvnw3OXe9MqG19XdeENA1KyhK5rqjpwdvPGfSn2V+SlsdJA0DFsobUScD9qXQw\n\tOvhapHe3XboK2+Rd7L+g/9Ud7ZKLQHAsMBXOVJbufA1AT+IaOt0ugMcFkAR5UbBg5+dZUYJj\n\t1QbPQcGmM3wfvuaWV5+SlJ+WeKIb8ta5Ag0EVgT9ZgEQAM4o5G/kmruIQJ3K9SYzmPishRHV\n\tDcUcvoakyXSX2mIoccmo9BHtD9MxIt+QmxOpYFNFM7YofX4lG0ld8H7FqoNVLd/+a0yru5Cx\n\tadeZBe3qr1eLns10Q90LuMo7/6zJhCW2w+HE7xgmCHejAwuNe3+7yt4QmwlSGUqdxl8cgtS1\n\tPlEK93xXDsgsJj/bw1EfSVdAUqhx8UQ3aVFxNug5OpoX9FdWJLKROUrfNeBE16RLrNrq2ROc\n\tiSFETpVjyC/oZtzRFnwD9Or7EFMi76/xrWzk+/b15RJ9WrpXGMrttHUUcYZEOoiC2lEXMSAF\n\tSSSj4vHbKDJ0vKQdEFtdgB1roqzxdIOg4rlHz5qwOTynueiBpaZI3PHDudZSMR5Fk6QjFooE\n\tXTw3sSl/km/lvUFiv9CYyHOLdygWohvDuMkV/Jpdkfq8XwFSjOle+vT/4VqERnYFDIGBxaRx\n\tkoBLfNDiiuR3lD8tnJ4A1F88K6ojOUs+jndKsOaQpDZV6iNFv8IaNIklTPvPkZsmNDhJMRHH\n\tIu60S7BpzNeQeT4yyY4dX9lC2JL/LOEpw8DGf5BNOP1KgjCvyp1/KcFxDAo89IeqljaRsCdP\n\t7WCIECWYem6pLwaw6IAL7oX+tEqIMPph/G/jwZcdS6Hkyt/esHPuHNwX4guqTbVEuRqbDzDI\n\t2DJO5FbxABEBAAGJAiUEGAEKAA8CGwwFAlnDlGsFCQeA/gIACgkQoR5GchCkYf1yYRAAq+Yo\n\tnbf9DGdK1kTAm2RTFg+w9oOp2Xjqfhds2PAhFFvrHQg1XfQR/UF/SjeUmaOmLSczM0s6XMeO\n\tVcE77UFtJ/+hLo4PRFKm5X1Pcar6g5m4xGqa+Xfzi9tRkwC29KMCoQOag1BhHChgqYaUH3yo\n\tUzaPwT/fY75iVI+yD0ih/e6j8qYvP8pvGwMQfrmN9YB0zB39YzCSdaUaNrWGD3iCBxg6lwSO\n\tLKeRhxxfiXCIYEf3vwOsP3YMx2JkD5doseXmWBGW1U0T/oJF+DVfKB6mv5UfsTzpVhJRgee7\n\t4jkjqFq4qsUGxcvF2xtRkfHFpZDbRgRlVmiWkqDkT4qMA+4q1y/dWwshSKi/uwVZNycuLsz+\n\t+OD8xPNCsMTqeUkAKfbD8xW4LCay3r/dD2ckoxRxtMD9eOAyu5wYzo/ydIPTh1QEj9SYyvp8\n\tO0g6CpxEwyHUQtF5oh15O018z3ZLztFJKR3RD42VKVsrnNDKnoY0f4U0z7eJv2NeF8xHMuiU\n\tRCIzqxX1GVYaNkKTnb/Qja8hnYnkUzY1Lc+OtwiGmXTwYsPZjjAaDX35J/RSKAoy5wGo/YFA\n\tJxB1gWThL4kOTbsqqXj9GLcyOImkW0lJGGR3o/fV91Zh63S5TKnf2YGGGzxki+ADdxVQAm+Q\n\tsbsRB8KNNvVXBOVNwko86rQqF9drZuw=","Organization":"Ideas on Board","Message-ID":"<33ee9dea-f115-555b-8130-873fd8770c70@ideasonboard.com>","Date":"Mon, 21 Jan 2019 09:34:42 +0000","User-Agent":"Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101\n\tThunderbird/60.2.1","MIME-Version":"1.0","In-Reply-To":"<20190121092646.GC4420@pendragon.ideasonboard.com>","Content-Type":"text/plain; charset=utf-8","Content-Language":"en-GB","Content-Transfer-Encoding":"7bit","Subject":"Re: [libcamera-devel] [PATCH] libcamera: v4l2_device: Return const\n\tstd::string","X-BeenThere":"libcamera-devel@lists.libcamera.org","X-Mailman-Version":"2.1.23","Precedence":"list","List-Id":"","List-Unsubscribe":",\n\t","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n\t","X-List-Received-Date":"Mon, 21 Jan 2019 09:34:45 -0000"}},{"id":444,"web_url":"https://patchwork.libcamera.org/comment/444/","msgid":"<20190121120430.GA12780@pendragon.ideasonboard.com>","date":"2019-01-21T12:04:30","subject":"Re: [libcamera-devel] [PATCH] libcamera: v4l2_device: Return const\n\tstd::string","submitter":{"id":2,"url":"https://patchwork.libcamera.org/api/people/2/","name":"Laurent Pinchart","email":"laurent.pinchart@ideasonboard.com"},"content":"Hi Kieran,\n\nOn Mon, Jan 21, 2019 at 09:34:42AM +0000, Kieran Bingham wrote:\n> On 21/01/2019 09:26, Laurent Pinchart wrote:\n> > On Mon, Jan 21, 2019 at 10:20:20AM +0100, Jacopo Mondi wrote:\n> >> Make getter functions of V4L2Device return std::string as the rest of\n> >> the library does.\n> >\n> > This is something that has been discussed during the review of Kieran's\n> > original patch I believe. The question was whether it would be more\n> > efficient to use const char * or a an std::string, and the answer to\n> > that question depends on the expected usage of those methods. If all\n> > users need an std::string, then I agree that the methods below can as\n> > well construct one. On the other hand, if some users need a const char\n> > *, it is a bit pointless to convert from const char * to std::string and\n> > then back to const char * using c_str(). This is why we have opted for\n> > const char * here.\n> \n> And because the compiler can automatically convert from a const char *\n> to a std::string using the string constructors ... so you can still use\n> these methods anywhere you would use a std::string...\n\nNote that in that case the std::string constructor will be inlined,\nwhich can be an issue if the function returning const char * is called\nfrom a very large number of places. In this specific case the functions\nare themselves inlined anyway, so it would make very little difference.\n\n> > This is a generic question that we should ask ourselves through the\n> > library. Anyone with free time to analyze the problem ? :-)\n> > \n> >> Signed-off-by: Jacopo Mondi \n> >> ---\n> >> src/libcamera/include/v4l2_device.h | 6 +++---\n> >> 1 file changed, 3 insertions(+), 3 deletions(-)\n> >>\n> >> diff --git a/src/libcamera/include/v4l2_device.h b/src/libcamera/include/v4l2_device.h\n> >> index 474c05b..5fe3d82 100644\n> >> --- a/src/libcamera/include/v4l2_device.h\n> >> +++ b/src/libcamera/include/v4l2_device.h\n> >> @@ -45,9 +45,9 @@ public:\n> >> \tbool isOpen() const;\n> >> \tvoid close();\n> >>\n> >> -\tconst char *driverName() const { return caps_.driver(); }\n> >> -\tconst char *deviceName() const { return caps_.card(); }\n> >> -\tconst char *busName() const { return caps_.bus_info(); }\n> >> +\tconst std::string driverName() const { return std::string(caps_.driver()); }\n> >> +\tconst std::string deviceName() const { return std::string(caps_.card()); }\n> >> +\tconst std::string busName() const { return std::string(caps_.bus_info()); }\n> > \n> > If we wanted to return an std::string, we should drop the const as the\n> > string is returned by value.\n> > \n> >>\n> >> private:\n> >> \tstd::string devnode_;","headers":{"Return-Path":"","Received":["from perceval.ideasonboard.com (perceval.ideasonboard.com\n\t[213.167.242.64])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTPS id 4952760C7F\n\tfor ;\n\tMon, 21 Jan 2019 13:04:31 +0100 (CET)","from pendragon.ideasonboard.com\n\t(dfj612yyyyyyyyyyyyyby-3.rev.dnainternet.fi\n\t[IPv6:2001:14ba:21f5:5b00::2])\n\tby perceval.ideasonboard.com (Postfix) with ESMTPSA id A454953E;\n\tMon, 21 Jan 2019 13:04:30 +0100 (CET)"],"DKIM-Signature":"v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com;\n\ts=mail; t=1548072270;\n\tbh=y+NEF8E3HHg2v/Zih4EvIRHyBrJUMYgz3mA6n6/0jpk=;\n\th=Date:From:To:Cc:Subject:References:In-Reply-To:From;\n\tb=DVWMMsd32t2U+x794AJBCLSO25UJusnPMoqWLjcYRBSwzoLC9ome4bzL+3yOhfBgS\n\tjPA6M81lBE20zHF2eoor/BE6JuZFy9JVlRMluuNCqTOUuCqSskBjmirSkkOSvU7yVP\n\t62r+nDQQRcKG0iglRKLrG/wKHhfh0Hkf9vH6W0xk=","Date":"Mon, 21 Jan 2019 14:04:30 +0200","From":"Laurent Pinchart ","To":"Kieran Bingham ","Cc":"Jacopo Mondi , libcamera-devel@lists.libcamera.org","Message-ID":"<20190121120430.GA12780@pendragon.ideasonboard.com>","References":"<20190121092020.4145-1-jacopo@jmondi.org>\n\t<20190121092646.GC4420@pendragon.ideasonboard.com>\n\t<33ee9dea-f115-555b-8130-873fd8770c70@ideasonboard.com>","MIME-Version":"1.0","Content-Type":"text/plain; charset=utf-8","Content-Disposition":"inline","In-Reply-To":"<33ee9dea-f115-555b-8130-873fd8770c70@ideasonboard.com>","User-Agent":"Mutt/1.10.1 (2018-07-13)","Subject":"Re: [libcamera-devel] [PATCH] libcamera: v4l2_device: Return const\n\tstd::string","X-BeenThere":"libcamera-devel@lists.libcamera.org","X-Mailman-Version":"2.1.23","Precedence":"list","List-Id":"","List-Unsubscribe":",\n\t","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n\t","X-List-Received-Date":"Mon, 21 Jan 2019 12:04:31 -0000"}}]