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NNTP-Posting-Date: Wed, 23 Sep 2015 13:40:01 -0500
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Newsgroups: comp.lang.c++.moderated
From: Bo Persson <bop@gmb.dk>
Subject: Re: reusing objects after std::vector.emplace
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Date: Wed, 23 Sep 2015 13:34:25 CST
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Xref: csiph.com comp.lang.c++.moderated:7334


On 2015-09-23 15:27, Ralf Fassel wrote:
>
> Having not understood completely and absolutely in all depth the concept
> of rvalue references, I hope the following is not an FAQ...
>
> My understanding was that after an move operation on an object, one
> should not further deal with it:
>
>      #include <vector>
>      #include <string>
>      #include <sstream>
>
>      void split_string(const std::string & s, std::vector<std::string> &
v) {
>        std::istringstream sstrm(s);
>
>        std::string str;
> // here we're reusing str after the emplace_back, is this ok?
>        while(sstrm >> str) v.emplace_back(str);
>      }
>
> Should this loop better be
>
>      while (1) {
>        std::string str;
>        if (!(sstrm >> str)) break;
>        v.emplace_back(str);
>      }
>
> Somehow I feel that the >> operator in the first example could do
> nothing worse than the DTOR in the second, so both should be ok?
>


The original code is ok. The moved from string is defined to be in a 
consistent state and can be assigned a new value.


Bo Persson


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