1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
|
Delivered-To: raj.khem@gmail.com
Received: by 2002:a05:620a:20d3:0:0:0:0 with SMTP id f19csp2716715qka;
Sat, 27 Mar 2021 19:58:30 -0700 (PDT)
X-Google-Smtp-Source: ABdhPJwyDnjZqZmFqHVShb/5/RoVkJ4Avv5bcnyuo85vIRR2vJDQF+QBZpQpEWHgx5GuEuwLVSC+
X-Received: by 2002:a05:6512:22d0:: with SMTP id g16mr12125441lfu.650.1616900310724;
Sat, 27 Mar 2021 19:58:30 -0700 (PDT)
ARC-Seal: i=1; a=rsa-sha256; t=1616900310; cv=none;
d=google.com; s=arc-20160816;
b=bZlu68tossyE2YcGkt0HzIhqTUroWDT/EgJvAiQBgZ6bPzMJ+wjwWp3LzViqOxiRPQ
r0cFyme7CJ9YRf2TLmpjGuv2RPQ+EkrtFdlB7i65nhDrwvBoxt78vF2tUoDgVLL1YrU9
wKgHPtBjtDcDveOXKQJH2j5HRwiBjCXlPRBhlSxV8kJPBj//dRaKm0MsxfiW/IgyN1tZ
FFxfe4Lk1Awm8ZKAklhdKMly3MFA6IbnjwNcN/84a0R/0+PLu9X8XIR6+CnrfqSgWOBx
zsV8p3HuVQTpX7Hhnkiz7PYudHsJJ/7KXeXTP6s9NNnZGu9A6U/E6VOob5BSm9DDIA5z
4AnA==
ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816;
h=content-transfer-encoding:mime-version:message-id:date:subject:cc
:to:from:dkim-signature;
bh=fbAn+wsNks5BGTY34H4T90NDFJaNV4nnt9vc9DBFaWQ=;
b=mLZNiQR/CdgcVTAc7OQmK0ZYTVpofG/EOqTIi2NYIYFhanWhatYY9Hx2xwxIp6kQ5R
n0uXh5tLth6aPYD09z3YcXYasEIszBKwoNUFjRA85lFm3d5/J2S1wC5rBy25QeCDOg57
QdzYrTBX2QGRHGQKauEnX5FLDTT+I53sPa87TyvxUKBS+lTAbJig70KfmL7FJIEWT1ZI
CZKCErYFlQTGNnwM0CYVXyHv54D2tA25veHQIJN8KK+XObNWuAY3rYpqKoUpOP4vpSPi
MXJWAV4L6NZEShWvwJiC4Zdy2xFzXASX27CAKIsX6T5Rub03grVTg6WVt9bChK1x5jeg
A2Yw==
ARC-Authentication-Results: i=1; mx.google.com;
dkim=pass (test mode) header.i=@ideasonboard.com header.s=mail header.b=MniKswyT;
spf=pass (google.com: domain of laurent.pinchart@ideasonboard.com designates 213.167.242.64 as permitted sender) smtp.mailfrom=laurent.pinchart@ideasonboard.com
Return-Path: <laurent.pinchart@ideasonboard.com>
Received: from perceval.ideasonboard.com (perceval.ideasonboard.com. [213.167.242.64])
by mx.google.com with ESMTPS id v18si12339470ljj.208.2021.03.27.19.58.30
for <raj.khem@gmail.com>
(version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256);
Sat, 27 Mar 2021 19:58:30 -0700 (PDT)
Received-SPF: pass (google.com: domain of laurent.pinchart@ideasonboard.com designates 213.167.242.64 as permitted sender) client-ip=213.167.242.64;
Authentication-Results: mx.google.com;
dkim=pass (test mode) header.i=@ideasonboard.com header.s=mail header.b=MniKswyT;
spf=pass (google.com: domain of laurent.pinchart@ideasonboard.com designates 213.167.242.64 as permitted sender) smtp.mailfrom=laurent.pinchart@ideasonboard.com
Received: from pendragon.lan (62-78-145-57.bb.dnainternet.fi [62.78.145.57])
by perceval.ideasonboard.com (Postfix) with ESMTPSA id 11F12332;
Sun, 28 Mar 2021 04:58:28 +0200 (CEST)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com;
s=mail; t=1616900309;
bh=BwCg4h9N9fJysbMT1Yjbazbp7zTImD9mkWJSjCKzCmg=;
h=From:To:Cc:Subject:Date:From;
b=MniKswyT+aUtPgeMFeLqW6cRMFsPRN4W1XtVDA6pqI0QTSSx5koEuzSfEybjs6Qbp
ZdQar1r5nBIRCg9uq85YoLKoFeT7WN4PrwnRYPwaYGAFHfV44rDrq4RBe3VOIb+85W
tKn4HEzjlFelrImVbeymBsgpVhITveSVH1MdYRsE=
From: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To: libcamera-devel@lists.libcamera.org
Cc: Khem Raj <raj.khem@gmail.com>
Subject: [PATCH v2] libcamera: pipeline: uvcvideo: Avoid reference to temporary object
Date: Sun, 28 Mar 2021 05:57:41 +0300
Message-Id: <20210328025741.30246-1-laurent.pinchart@ideasonboard.com>
X-Mailer: git-send-email 2.28.1
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
From: Khem Raj <raj.khem@gmail.com>
A range-based for loop whose range expression is an array of char
pointers and range variable declaration is a const reference to a
std::string creates a temporary string from the char pointer and binds
the range variable reference to it. This creates a const reference to a
temporary, which is valid in C++, and extends the lifetime of the
temporary to the lifetime of the reference.
However, lifetime extension in range-based for loops is considered as a
sign of a potential issue, as a temporary is created for every
iteration, which can be costly, and the usage of a reference in the
range declaration doesn't make it obvious that the code isn't simply
binding a reference to an existing object. gcc 11, with the
-Wrange-loop-construct option, flags this:
uvcvideo.cpp:432:33: error: loop variable 'name' of type 'const string&' {aka 'const std::__cxx11::basic_string<cha
r>&'} binds to a temporary constructed from type 'const char* const' [-Werror=range-loop-construct]
| 432 | for (const std::string &name : { "idVendor", "idProduct" }) {
| | ^~~~
To please the compiler, make the range variable a const char *. This may
bring a tiny performance improvement, as the name is only used once, in
a location where the compiler can use
operator+(const std::string &, const char *)
instead of
operator+(const std::string &, const std::string &)
Signed-off-by: Khem Raj <raj.khem@gmail.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Use a const char * type instead of auto, and update the commit message
accordingly.
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
---
src/libcamera/pipeline/uvcvideo/uvcvideo.cpp | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/src/libcamera/pipeline/uvcvideo/uvcvideo.cpp b/src/libcamera/pipeline/uvcvideo/uvcvideo.cpp
index 031f96e28449..b6c6ade5ebaf 100644
--- a/src/libcamera/pipeline/uvcvideo/uvcvideo.cpp
+++ b/src/libcamera/pipeline/uvcvideo/uvcvideo.cpp
@@ -429,7 +429,7 @@ std::string PipelineHandlerUVC::generateId(const UVCCameraData *data)
/* Creata a device ID from the USB devices vendor and product ID. */
std::string deviceId;
- for (const std::string &name : { "idVendor", "idProduct" }) {
+ for (const char *name : { "idVendor", "idProduct" }) {
std::ifstream file(path + "/../" + name);
if (!file.is_open())
--
Regards,
Laurent Pinchart
|
