title: Can't link GTKmm 3 app with minGW64 ithin MSYS2: ustring constructor not found
body: <p>I was trying to compile my GTKmm 3 app on Windows. Get an error during compilation that Glib::ustring doesn't have a constructor  </p>
  
  <pre><code>    Glib:: ustring:: ustring(std::string*)  
  </code></pre>
  
  <p>although the code gets compiled successfully on Ubuntu.</p>
  
  <p>Sample code:</p>
  
  <pre><code>#include &lt;gtkmm.h&gt;
  #include &lt;string&gt;
  
  int main()
  {
      std::string a("aa");
      Glib::ustring b(a);
      return 0;
  }
  </code></pre>
  
  <p>Compiling with:  </p>
  
  <pre><code>g++ -std=c++14  -c test.cpp `pkg-config gtkmm-3.0 --cflags` &amp;&amp; \
  g++ test.o `pkg-config --libs gtkmm-3.0`
  </code></pre>
  
  <p>Output (on Windows 10 x64, MSYS2 MinGW64):</p>
  
  <pre><code>test.o:test.cpp:(.text+0x51): undefined reference to `Glib::ustring::ustring(std::string const&amp;)'
  test.o:test.cpp:(.text+0x51): relocation truncated to fit: R_X86_64_PC32 against undefined symbol `Glib::ustring::ustring(std::string const&amp;)'
  collect2: error: ld returned 1 exit status
  </code></pre>
  
  <p>Windows: Glib 2.50.3, Glibmm 2.50.0, GCC 5.3.0 (MinGW 64bit)<br>
  Ubuntu: Glib 2.48.1, Glibmm 2.46.3, GCC 5.4.0</p>