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authorKhem Raj <raj.khem@gmail.com>2021-03-03 15:21:26 -0800
committerLaurent Pinchart <laurent.pinchart@ideasonboard.com>2021-03-28 22:56:31 +0300
commit299e8ef563a83ce6e9624bb21e11ecb2ad5a228f (patch)
treeb31ac4bd984de718bcd219af5b84d8fa82018a5c
parent3d3e6fcdb92a7d337f3e5472f0f989f625f8985e (diff)
pipeline: uvcvideo: Avoid reference to temporary object
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>
-rw-r--r--src/libcamera/pipeline/uvcvideo/uvcvideo.cpp2
1 files changed, 1 insertions, 1 deletions
diff --git a/src/libcamera/pipeline/uvcvideo/uvcvideo.cpp b/src/libcamera/pipeline/uvcvideo/uvcvideo.cpp
index 031f96e2..b6c6ade5 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())