警告从Lambda返回捕获的引用 [英] Warning returning a captured reference from a lambda

问题描述

我尝试使用lambda有条件地将引用绑定到两个变量之一:

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;
    }
}();

这会在clang 3.4中产生警告:

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;
                   ^~~

但是我只返回对调用lambda范围内的堆栈内存的引用.此行为是指定的，未指定的还是叮叮当当的错误?

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?

推荐答案

这确实是Clang中的一个错误-您正确地通过引用捕获了两个变量，并且没有创建任何悬挂的引用.我认为Clang每次有人返回对内部变量(无论是lambda还是函数)的引用时，都会自动发出警告.

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 不再显示此警告，

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

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