Scope operator needed to find std namespace instead of boost

Question

I am working on porting parts of the boost library to compile under cuda / nvcc as device functions. This involves using the thrust library for some things like iterators, arrays, etc. One issue I am finding is a compile error in the thrust library such as:

    C:\Program Files\NVIDIA GPU Computing Toolkit\CUDA\v9.1\include\thrust/iterator/iterator_traits.h(66): error : namespace "boost::std" has no member "ptrdiff_t"

which is triggered by the line in thrust:

   typedef std::ptrdiff_t difference_type;

I can fix this by adding the scope operator :: ahead of the std lib call like:

   typedef ::std::ptrdiff_t difference_type;

but clearly it is not okay to modify thrust.

Does anyone know why I am getting this issue? i.e. why does the thrust header iterator_traits.h search for std::ptrdiff_t inside the namespace boost::std rather than std? Is there a way to reverse this before I include the thrust header?

It is not easy to provide a minimal working example here due to the nature of porting a large library like boost.

Thanks!

Include the thrust headers before the boost ones? Also, are you using using namespace directives? — NathanOliver
– NathanOliver, Commented Dec 28, 2018 at 1:05
I'm amending the thousands of boost include files to be device compatible. So the thrust includes are deep inside the body of boost. Boost uses lots of using namespace directives. — john_smith_lon
– john_smith_lon, Commented Dec 28, 2018 at 1:09
The device port is already working for some special functions. I have hope but agree it is pretty ambitious. — john_smith_lon
– john_smith_lon, Commented Dec 28, 2018 at 19:08

Corristo · Accepted Answer · 2018-12-28 02:37:14Z

4

I can only guess here, but my best guess is that for some reason there is a missing closing curly brace to close the boost namespace somewhere before the std namespace is opened, probably by including a standard library header. This then causes the namespace boost::std to exist so the compiler looks in that sub-namespace for std::ptrdiff_t as the boost namespace is currently open.

E.g. compiling the following source file with gcc

#include <cstddef>

namespace foo {

// this creates a namespace ::foo::std
#include <typeinfo>

}

namespace foo {
    using difference_type = std::ptrdiff_t;
}

also prints

prog.cc:11:34: error: 'ptrdiff_t' in namespace 'foo::std' does not name a type
   11 |     using difference_type = std::ptrdiff_t;
      |                                  ^~~~~~~~~

as you can also see here.

answered Dec 28, 2018 at 2:37

Corristo

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1 Comment

john_smith_lon Over a year ago

Thank you - this was it. Much appreciated!

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