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>
Khem Raj
299e8ef563