id	summary	reporter	owner	description	type	status	milestone	component	version	severity	resolution	keywords	cc
5631	nvcc's pre-processor breaks boost/lexical_cast.hpp	Rich Wareham <rjw57@…>	Antony Polukhin	"The `nvcc` compiler fails to compile a trivial file which just `#include`s the `boost/lexical_cast.hpp` header. `g++` compiles the file correctly.

{{{
rjw57@spica:~$ cat foo.cpp
#include <boost/lexical_cast.hpp>
rjw57@spica:~$ cat foo.cu
#include <boost/lexical_cast.hpp>
rjw57@spica:~$ /usr/bin/g++-4.4 -c foo.cpp
rjw57@spica:~$ /usr/bin/nvcc --compiler-bindir=/usr/bin/g++-4.4 -c foo.cu
/usr/include/boost/lexical_cast.hpp(352): error: expected an expression

1 error detected in the compilation of ""/tmp/tmpxft_00001520_00000000-4_foo.cpp1.ii"".
}}}

The problem is with `nvcc`'s pre-processor which can be observed by using `-E` and grepping for `// == 1` in the output:

{{{
rjw57@spica:~$ /usr/bin/g++-4.4 -E -o foo-gcc.i foo.cpp
rjw57@spica:~$ /usr/bin/nvcc --compiler-bindir=/usr/bin/g++-4.4 -E -o foo-nvcc.i foo.cu
rjw57@spica:~$ ack-grep '\/\/ == 1' foo*.i
foo-nvcc.i
73304:            static const std::size_t value = std::numeric_limits<Source>::is_signed + std::numeric_limits<Source>::is_specialized + // == 1 std::numeric_limits<Source>::digits10 * 2;
}}}

The `nvcc` pre-processor does not strip comments from the input to the compiler and appears to be removing new-lines. The `gcc` compiler does strip the comments.

This is possibly a bug in `nvcc` but I suggest a workaround could be put into boost itself without too much pain. Also I suspect it'd take a standards lawyer to work out who is in the wrong here.

The troublesome line (number 345 in 1.4.2) is in the `boost/lexical_cast.hpp` file. This problem is still present in the SVN trunk.

{{{
...
        template<class Source>
        struct lcast_src_length_integral
        {
#ifndef BOOST_NO_LIMITS_COMPILE_TIME_CONSTANTS
            BOOST_STATIC_CONSTANT(std::size_t, value =
                  std::numeric_limits<Source>::is_signed +
                  std::numeric_limits<Source>::is_specialized + // == 1
                  std::numeric_limits<Source>::digits10 * 2
              );
#else
            BOOST_STATIC_CONSTANT(std::size_t, value = 156);
            BOOST_STATIC_ASSERT(sizeof(Source) * CHAR_BIT <= 256);
#endif
        };
...
}}}

A suggested workaround is removing the C++-style comment or replacing it with a C-style one?"	Bugs	closed	Boost 1.48.0	lexical_cast	Boost 1.42.0	Problem	fixed	nvcc lexical_cast pre-processor