How to test if a iterator is valid or not?
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From: Peng Yu on 14 Jun 2010 18:16 Suppose I have an std::vector<int>::iterator that I get from somewhere else. I'm not sure if it is properly initialized. Is there a way to test in runtime? -- [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ]
From: Ulrich Eckhardt on 14 Jun 2010 23:09 Peng Yu wrote: > Suppose I have an std::vector<int>::iterator that I get from somewhere > else. I'm not sure if it is properly initialized. Is there a way to > test in runtime? No. You are expected to write your code in a way that invalid iterators don't happen, everything else is just "undefined behaviour". That said, many major implementations provide a mode that sacrifices complexity guarantees and efficiency for additional checks, which you can use for debugging. Uli -- Sator Laser GmbH Geschäftsführer: Thorsten Föcking, Amtsgericht Hamburg HR B62 932 [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ]
From: Daniel Krügler on 14 Jun 2010 23:10 On 15 Jun., 11:16, Peng Yu <pengyu...(a)gmail.com> wrote: > Suppose I have an std::vector<int>::iterator that I get from somewhere > else. I'm not sure if it is properly initialized. Is there a way to > test in runtime? There does not exist a general test function for this. This is so, because pointers are iterators and there also exists no general/portable mechanism to verify whether a pointer value is valid: int main() { int* p, q; // not initialized if (p == q) ; // Undefined behaviour } HTH & Greetings from Bremen, Daniel Kr�gler -- [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ]
From: Jens Schmidt on 14 Jun 2010 23:13 Peng Yu wrote: > Suppose I have an std::vector<int>::iterator that I get from somewhere > else. I'm not sure if it is properly initialized. Is there a way to > test in runtime? No, you can't test that. It is bad design to use uninitialized iterators in C++, the same as with any other uninitialized data. Someone giving you this iterator will get what he/she deserves: unspecified behaviour. -- Greetings, Jens Schmidt [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ]
From: Leigh Johnston on 14 Jun 2010 23:48
"Peng Yu" <pengyu.ut(a)gmail.com> wrote in message news:6680bd0a-33c3-4f0a-aa5d-6c65959cd5db(a)k39g2000yqb.googlegroups.com... > Suppose I have an std::vector<int>::iterator that I get from somewhere > else. I'm not sure if it is properly initialized. Is there a way to > test in runtime? > The only valid operations on an invalid iterator are initialization and assignment so the answer to your question is "no". /Leigh -- [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] |