Fix for GCC 5.3.1, Ubuntu 16.04 LTS, 64-bit

Created by: abclogin

I compile on Ubuntu 16.04 LTS 64-bit using GCC 5.3.1, GPP 2.24

Error in:

[ 3%] Building CXX object CMakeFiles/handystats.dir/src/config.cpp.o In file included from /builds/handystats/src/config.cpp:31:0: /builds/handystats/include/handystats/rapidjson/writer.h: In member function ‘void rapidjson::Writer<OutputStream, SourceEncoding, TargetEncoding, Allocator>::WriteDouble(double)’: /builds/handystats/include/handystats/rapidjson/writer.h:167:14: warning: there are no arguments to ‘isnan’ that depend on a template parameter, so a declaration of ‘isnan’ must be available [-fpermissive] if (isnan(d)) { ^ /home/username/coca/handystats/include/handystats/rapidjson/writer.h: In instantiation of ‘void rapidjson::Writer<OutputStream, SourceEncoding, TargetEncoding, Allocator>::WriteDouble(double) [with OutputStream = rapidjson::GenericStringBufferrapidjson::UTF8<, rapidjson::MemoryPoolAllocator<> >; SourceEncoding = rapidjson::UTF8<>; TargetEncoding = rapidjson::UTF8<>; Allocator = rapidjson::MemoryPoolAllocator<>]’: /builds/handystats/include/handystats/rapidjson/writer.h:49:62: required from ‘rapidjson::Writer<OutputStream, SourceEncoding, TargetEncoding, Allocator>& rapidjson::Writer<OutputStream, SourceEncoding, TargetEncoding, Allocator>::Double(double) [with OutputStream = rapidjson::GenericStringBufferrapidjson::UTF8<, rapidjson::MemoryPoolAllocator<> >; SourceEncoding = rapidjson::UTF8<>; TargetEncoding = rapidjson::UTF8<>; Allocator = rapidjson::MemoryPoolAllocator<>]’ /builds/handystats/include/handystats/rapidjson/document.h:552:13: required from ‘const rapidjson::GenericValue<Encoding, Allocator>& rapidjson::GenericValue<Encoding, Allocator>::Accept(Handler&) const [with Handler = rapidjson::Writerrapidjson::GenericStringBuffer<rapidjson::UTF8<, rapidjson::MemoryPoolAllocator<> > >; Encoding = rapidjson::UTF8<>; Allocator = rapidjson::MemoryPoolAllocator<>]’ /builds/handystats/src/config.cpp:199:22: required from here /builds/handystats/include/handystats/rapidjson/writer.h:167:12: error: ‘isnan’ was not declared in this scope if (isnan(d)) { ^ /builds/handystats/include/handystats/rapidjson/writer.h:167:12: note: suggested alternative: In file included from /builds/handystats/include/handystats/rapidjson/writer.h:9:0, from /builds/handystats/src/config.cpp:31: /usr/include/c++/5/cmath:641:5: note: ‘std::isnan’ isnan(_Tp __x) ^ CMakeFiles/handystats.dir/build.make:254: recipe for target 'CMakeFiles/handystats.dir/src/config.cpp.o' failed make[2]: *** [CMakeFiles/handystats.dir/src/config.cpp.o] Error 1 CMakeFiles/Makefile2:67: recipe for target 'CMakeFiles/handystats.dir/all' failed make[1]: *** [CMakeFiles/handystats.dir/all] Error 2 Makefile:138: recipe for target 'all' failed make: *** [all] Error 2

I read this answer:

http://stackoverflow.com/a/18129007

It depends on which header you include. If you include the C header <math.h> (which is part of C++, albeit marked as deprecated), then you can use the unqualified C functions, like isnan. If you on the other hand include the C++ header , you are only guaranteed that it brings all the functions from <math.h> into the std namespace and thus you have to properly qualify them, like std::isnan (or use some kind of using directive). Unfortunately an implementation is allowed but not required to bring those functions into the global namespace, too, when including (and thus it is one of the many "works on my machine"-incidences of C++ and the reason why many people write code like you just tried to compile unsuccessfully).

So to sum up: Either include <math.h> and use isnan or include and use std::isnan, everything else is non-portable. Of course all this applies to any other C header and its respective C++ version, too.

EDIT: It should be noted though, that this particular function isnan is only supported since C++11 and wasn't available in C++98 at all (which may be part of your confusion). But this doesn't change anything in this situation because in C++98 neither nor <math.h> (which was the actual C89/C90 header back then and not the C99 header that C++11 includes) had this function, since they're always in-sync. So what this library from your question maybe tried was to use C++98 while taking the isnan function from a different C99 implementation (which isn't a particularly good idea, as it might conflict with the C89/C90 parts of the C++ implementation, never even tried this though).

I added "std::" prefix to isnan call. Compilation is successfully.

Attention!

It may be incompatible with older versions of the compiler.