CODEWITHSUNDEEP
c++c++11lambda
s4y
s4y

Reputation: 51685

Warning returning a captured reference from a lambda

I tried to use a lambda to conditionally bind a reference to one of two variables:

int foo, bar;
int &choice = [&]() -> int & {
    if (true /* some condition */) {
        return foo;
    } else {
        return bar;
    }
}();

This yields a warning in clang 3.4:

stack_stuffing.cpp:5:20: warning: reference to stack memory associated with
      local variable 'foo' returned [-Wreturn-stack-address]
            return foo;
                   ^~~
stack_stuffing.cpp:7:20: warning: reference to stack memory associated with
      local variable 'bar' returned [-Wreturn-stack-address]
            return bar;
                   ^~~

But I only ever return references to stack memory that's in scope where the lambda is called. Is this behavior specified, unspecified, or a clang bug?

Upvotes: 4

Views: 387

Answers (1)

Columbo
Columbo

Reputation: 60979

This is indeed a bug in Clang - you are correctly capturing both variables by reference and no dangling references are created. I presume Clang automatically issued a warning every time someone returned a reference to a stack variable inside anything, be it a lambda or a function.

Clang 3.5 does not show this warning anymore, neither does GCC 4.9.0.

Upvotes: 4

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