is there a runtime error here when you call the get method?
Code:#include <string>
using namespace std;
class A {
public:
string& get() {
string abc = "abc";
return abc;
}
};
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is there a runtime error here when you call the get method?
Code:#include <string>
using namespace std;
class A {
public:
string& get() {
string abc = "abc";
return abc;
}
};
Why not just test and see? Of course, even if you do not get a runtime error, returning a reference to a local variable is still wrong.
Why not just test and see? Of course, even if you do not get a runtime error, returning a reference to a local variable is still wrong.
Are you sure that even for a arge system we get an error?
Large or small, it does not matter. It is wrong since the caller would refer to an object that no longer exists.Quote:
Are you sure that even for a arge system we get an error?
The question here is that is getting a runtime error a garuntee? I agree that it is wrong to refer to a local variable when it gets out of scope but in a large system is there a one in a million chance of getting abc backQuote:
Originally Posted by laserlight
Runtime error? That should return a compiler error or warning.
Whatever you may say, returning a local variable is always wrong.
Returning a reference or pointer to a local variable is wrong. Returning the variable by value, of course, is not.Quote:
Originally Posted by Elysia
But that's not the issue here, is it? ;)Quote:
Originally Posted by brewbuck
What is your rationale for wanting to know if there is such a guarantee?Quote:
The question here is that is getting a runtime error a garuntee?
To confirm that: I get a compiler warning on the MinGW port of g++ 3.4.2.Quote:
That should return a compiler error or warning.
No, but it is what you, intentionally or not, said.Quote:
Originally Posted by Elysia
Is it? That was never my intention, though it is correct: returning by value is safe, returning by reference is not. This is in regards to a local variable or object.Quote:
Originally Posted by CornedBee
I believe what you'll get in that case is 'undefined behavior'. You might be able to reference the memory of the string you returned and it might work fine if that memory hasn't been overwritten; but then again, it could quite easily blow up (if you're lucky).Quote:
Originally Posted by rnx40401
So the simple answer is: Don't use variables beyond their lifetime.
As I asked earlier is there a remote chance of getting abc back in a large system? I guess it would behave differently on a laptop from a 1500 system environmentQuote:
Originally Posted by laserlight
No! Don't count on it!Quote:
Originally Posted by rnx40401
Keep it by returning a pointer or by value.
It's even harder in big systems since the (mow) freed memory will be overwritten.
I agree that getting abc back would be harder in a big system but in which case do we get a runtime error? when the memory is freed or when the memory is overwritten. My guess is that when the memory is overwritten we get some garbage back and no runtime error.Quote:
Originally Posted by Elysia