Visual Studio 2019 gives C26444 with cout.imbue

Question

When I use Visual Studio 2019, it gives me the green squiggles with this:

#include <iostream>
#include <locale>

int main() {
    // Green squiggles given for this entire line:
    std::cout.imbue(std::locale("en_US.utf8"));
    // Visual Studio says, "C26444: Avoid unnamed objects with custom construction and destruction (es.84)"

    // Using cout.imbue to provide nice formatting for numbers:
    std::cout << "Example locale formatting:  " << 100'000.00 << '\n';
}

I've tried some variations like this:

std::locale my_locale("en_US.utf8");
// Now the green squiggles just appear from cout.imbue onward:
std::cout.imbue(my_locale);

I believe the es.84 is from the C++ Core Guidelines: https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#Res-noname

However, I'm not sure how to fix this. I looked at cppreference.com and cplusplus.com for examples, but I'm doing what they show.

What does Visual Studio not like and how can I fix it?

Answer 1

The Visual Studio compiler (MSVC) doesn't 'like' the fact that you haven't named the return value of the call to imbue . Whether or not this warning is 'justified' is not for me to say; however, it is easy to add code to prevent the warning, by assigning the returned value to a named variable:

std::locale loc = std::cout.imbue(std::locale("en_US.utf8"));

Without this, the compiler assumes there is a call to the std::locale destructor on the unnamed (and otherwise unused) returned locale object (which there may well be).