Biagio Festa Biagio Festa - 3 years ago 253
C++ Question

Clang Warning on expression side effects

Given the following source code:

#include <memory>
#include <typeinfo>

struct Base {
virtual ~Base();
};

struct Derived : Base { };

int main() {
std::unique_ptr<Base> ptr_foo = std::make_unique<Derived>();

typeid(*ptr_foo).name();

return 0;
}


and compiled it with:

clang++ -std=c++14 -Wall -Wextra -Werror -Wpedantic -g -o test test.cpp


Enviroment setup:

linux x86_64
clang version 5.0.0


It does not compile because of warning (note
-Werror
):

error: expression with side effects will be evaluated
despite being used as an operand to 'typeid'
[-Werror,-Wpotentially-evaluated-expression]
typeid(*ptr_foo).name();


(Just a note: GCC does not claim that kind of potential problematic)




Question

Is there a way to get the information about the type pointed by a
unique_ptr
without generating that kind of warning?

Note: I am not talking about disabling
-Wpotentially-evaluated-expression
or avoiding
-Werror
.

Answer Source

Looks like following should work without warnings and give correct result for derived class

std::unique_ptr<Foo> ptr_foo = std::make_unique<Bar>();

if(ptr_foo.get()){
    auto& r = *ptr_foo.get();
    std::cout << typeid(r).name() << '\n';
}
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