1) The compilation has been further, you can modify "src/3rdParty/salomesmesh/inc/Rn.h".
2) But a second problem appeared.
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[ 9%] Generating version_check
git
/home/mainuser/softwares/freecad_source/build_2019-08-20/src/Build/Version.h.out written
[ 9%] Generating Version.h
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[ 36%] Building CXX object src/Mod/Part/App/CMakeFiles/Part.dir/PropertyTopoShape.cpp.o
/home/mainuser/softwares/freecad_source/src/Mod/Part/App/PropertyTopoShape.cpp: In function ‘Standard_Boolean BRepTools_Write(const TopoDS_Shape&, Standard_CString)’:
/home/mainuser/softwares/freecad_source/src/Mod/Part/App/PropertyTopoShape.cpp:285:3: error: ‘ofstream’ was not declared in this scope
ofstream os;
^~~~~~~~
/home/mainuser/softwares/freecad_source/src/Mod/Part/App/PropertyTopoShape.cpp:285:3: note: suggested alternatives:
In file included from /usr/include/c++/6/ios:38:0,
from /usr/include/c++/6/istream:38,
from /usr/include/c++/6/sstream:38,
from /home/mainuser/softwares/freecad_source/src/Mod/Part/App/PropertyTopoShape.cpp:27:
/usr/include/c++/6/iosfwd:165:34: note: ‘std::ofstream’
typedef basic_ofstream<char> ofstream;
^~~~~~~~
/usr/include/c++/6/iosfwd:165:34: note: ‘std::ofstream’
In file included from /home/mainuser/softwares/freecad_source/src/Base/Console.h:33:0,
from /home/mainuser/softwares/freecad_source/src/Mod/Part/App/PropertyTopoShape.cpp:52:
/home/mainuser/softwares/freecad_source/src/Base/Stream.h:306:7: note: ‘Base::ofstream’
class ofstream : public std::ofstream
^~~~~~~~
/home/mainuser/softwares/freecad_source/src/Mod/Part/App/PropertyTopoShape.cpp:287:18: error: ‘os’ was not declared in this scope
OSD_OpenStream(os, File, ios::out);
^~
/home/mainuser/softwares/freecad_source/src/Mod/Part/App/PropertyTopoShape.cpp:287:28: error: ‘ios’ has not been declared
OSD_OpenStream(os, File, ios::out);
^~~
src/Mod/Part/App/CMakeFiles/Part.dir/build.make:1445 : la recette pour la cible « src/Mod/Part/App/CMakeFiles/Part.dir/PropertyTopoShape.cpp.o » a échouée
make[2]: *** [src/Mod/Part/App/CMakeFiles/Part.dir/PropertyTopoShape.cpp.o] Erreur 1
CMakeFiles/Makefile2:1877 : la recette pour la cible « src/Mod/Part/App/CMakeFiles/Part.dir/all » a échouée
make[1]: *** [src/Mod/Part/App/CMakeFiles/Part.dir/all] Erreur 2
Makefile:127 : la recette pour la cible « all » a échouée
make: *** [all] Erreur 2