June 2011 - Boost-users - lists.boost.org

tokenizer
by asif saeed 01 Jun '11

01 Jun '11

Hi, Is boost tokenizer thread-safe? In an example in an online book, whose English translation link was provided a few days back, the tokenizer is created on stack. I have a hopeful presumption that the string operations it carries out are thread-safe. I need your help on this. Best regards, Asif

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Przemyslaw SLIWA is out of the office.
by przemyslaw.sliwa＠uk.bnpparibas.com 01 Jun '11

01 Jun '11

I will be out of the office starting 01/06/2011 and will not return until 02/06/2011. I will respond to your message when I return. ___________________________________________________________ This e-mail may contain confidential and/or privileged information. If you are not the intended recipient (or have received this e-mail in error) please notify the sender immediately and delete this e-mail. Any unauthorised copying, disclosure or distribution of the material in this e-mail is prohibited. Please refer to http://www.bnpparibas.co.uk/en/information/legal_information.asp?Code=ECAS-… for additional disclosures.

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[range] filtered dereferences underlying range elements twice
by Nathan Ridge 01 Jun '11

01 Jun '11

Hello, It seems that the 'filtered' adaptor dereferences elements of the underlying range twice if they pass the filter. This is illustrated in the following example, where a range is first transformed and then filtered: #include <iostream> #include <boost/range/adaptor/transformed.hpp> #include <boost/range/adaptor/filtered.hpp> #include <boost/range/algorithm/copy.hpp> int transform(int i) { std::cout << "calling transform() on " << i << "\n"; return i + 1; } bool filter(int i) { return i % 2 == 0; } int main() { int a[] = {1, 2, 3, 4, 5, 6, 7, 8}; int b[8]; boost::copy(a | boost::adaptors::transformed(transform) | boost::adaptors::filtered(filter), b); return 0; } The output is: calling transform() on 1 calling transform() on 1 calling transform() on 2 calling transform() on 3 calling transform() on 3 calling transform() on 4 calling transform() on 5 calling transform() on 5 calling transform() on 6 calling transform() on 7 calling transform() on 7 calling transform() on 8 As you can see, the transform function is called twice for elements that pass the filter. Can this be avoided? In my real use case, the transformation performs a database lookup, and it should not be done twice. Thanks, Nate.

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