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POTemporary non-const istream reference in constructor (C++)
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copied!<p>It seems that a constructor that takes a non-const reference to an istream cannot be constructed with a temporary value in C++.</p> <pre><code>#include <iostream> #include <sstream> using namespace std; class Bar { public: explicit Bar(std::istream& is) {} }; int main() { istringstream stream1("bar1"); Bar bar1(stream1); // OK on all platforms // compile error on linux, Mac gcc; OK on Windows MSVC Bar bar2(istringstream("bar2")); return 0; } </code></pre> <p>This compiles fine with MSVC, but not with gcc. Using gcc I get a compile error:</p> <pre><code>g++ test.cpp -o test test.cpp: In function ‘int main()’: test.cpp:18: error: no matching function for call to ‘Bar::Bar(std::istringstream)’ test.cpp:9: note: candidates are: Bar::Bar(std::istream&) test.cpp:7: note: Bar::Bar(const Bar&) </code></pre> <p>Is there something philosophically wrong with the second way (bar2) of constructing a Bar object? It looks nicer to me, and does not require that stream1 variable that is only needed for a moment.</p> <p><strong>EDIT</strong>: In response to Johannes Schaub's comment I'd like to give a bit more context. First, this is not the first time I have been annoyed by this behavior of C++, so I am genuinely interested in the higher level philosophical discussion of this issue. That said, in this particular case I have a class that reads in a file that contains data used to construct the object. I also like to write automated tests that use a string instead of the file. But using the file for construction is the primary use case. So I decided to make a constructor that takes an istream, so I could use either a file(stream), or a string(stream). That is how I got here. My test programs construct objects directly from strings, to simulate reading files. This saves me the trouble of creating separate data files for each little test.</p>

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