Re: Constness of return-by-value temporaries
Tom1s wrote:
I have a question, which I have asked on comp.lang.c++, but which no-one has
seemed willing to answer. Is the following translation unit well-formed, and
absent of undefined behaviour?
#include <string>
using std::string;
#include <vector>
using std::vector;
vector<string> Func()
{
vector<string> vec;
vec.push_back("One");
vec.push_back("Two");
return vec;
}
#include <iostream>
using std::cout; using std::endl;
int main()
{
const vector<string> &cvec = Func();
vector<string> &vec = const_cast< vector<string>& >(cvec);
vec.push_back("Three");
cout << vec.at(0) << endl
<< vec.at(1) << endl
<< vec.at(2) << endl;
}
Undefined behaviour!
See 8.5.3p8 [dcl.init.ref]
"--A temporary of type "cv1 T2" [sic] is created, and a constructor
is called to copy the entire rvalue object into the
temporary.
The reference is bound to the temporary or to a
sub-object
within the temporary.9)
"
Here cv1 is const... Thus the temporary is of type "const
std::vector<std::string>"
Modifying such temporary has UB.
It is clear that the type of the temporary is "cv1 T2", not "cv2 T2"
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