Copy const_iterator to std::string to save position

Question

Is it legal to make snapshots of const_iterator from the std::string class without invalidating it when performing ++ operations.

For example: If want to save the position in a string so I copy the current const_iterator:

std::string::const_iterator it = prev;

Now my parser continues with prev++. Is it still valid and points to the previous position of prev?

@alirakiyan Because that won't tell him what's guaranteed to happen. Sure, if it doesn't work, he knows it's useless. But if it does work, he knows nothing -- it may or may not be safe/legal/guaranteed. — David Schwartz, May 27 '17 at 11:01

πάντα ῥεῖ · Accepted Answer · 2017-05-27T11:05:47.423

3

Is it still valid and points to the previous position of prev?

Yes, as long the std::string isn't changed (in ways other than operator[] or at()) that's legal and the iterator snapshot is still valid.

edited May 27 '17 at 11:05

answered May 27 '17 at 10:56

You can change the characters in the string via `operator[]` or `at()` without invalidating any iterators. – John Zwinck May 27 '17 at 10:59
@John But the position will stay the same. – πάντα ῥεῖ May 27 '17 at 11:00
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I'm just trying to relax your statement that the iterator remains valid "as long as the string isn't changed." It remains valid as long as the string isn't changed in ways other than operator[] or at(). – John Zwinck May 27 '17 at 11:03
@John THX, adopted. – πάντα ῥεῖ May 27 '17 at 11:06
The string isn't changed while using any of the iterators to it. So it is guaranteed by the C++ standard to be safe? – Gustavo May 27 '17 at 11:06
@Gustavo Yes, it is. See [here](https://stackoverflow.com/questions/6438086/iterator-invalidation-rules). – πάντα ῥεῖ May 27 '17 at 11:07
The actual principle is that iterators remain valid as long as the string isn't resized or its capacity (potential size) changed. – Peter May 27 '17 at 11:11

1 Answers1