Re: pros and cons of returning const ref to string instead of string by value
On Dec 2, 10:58 pm, Stuart Golodetz
<sgolod...@NdOiSaPlA.pMiPpLeExA.ScEom> wrote:
X x;
const std::string& r = x.s(); // affected by subsequent x destruction
std::string s = x.s(); // not affected by subsequent x destruction
Whoa, stop, that's wrong! r is __not__ affected by x destruction,
because x gets destroyed __after__ r (sort to speak). Try thinking
like this, instead (that's what standard requires WRT variable
construction-destruction):
{ // x only available in this block
X x;
{ // r only available in this block
const std::string& r = x.s();
{ // s only available in this block
std::string s = x.s();
}
}
}
As you can see, it's not possible for r to be bad due to destroyed x.
What __is__ possible (and people make that mistake), is that you
somehow copy the reference somehow (to a pointer) and keep that after
x is destroyed, e.g.
const std::string* p;
{
X x;
const std::string& r = x.s(); // affected by subsequent x
destruction
p = &x; // Whoops!
std::string s = x.s(); // not affected by subsequent x destruction
}
p == "Undefined behavior";
Goran.
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