Trying to get rid of a c++ boost warning

Question

Whenever I include boost in my project I get a million of these warnings. Does anyone know how I can get rid of the warnings?

../depends\boost/config/abi_prefix.hpp(19) : warning C4103: 'depends\boost\config\abi_prefix.hpp' : alignment changed after including header, may be due to missing #pragma pack(pop)

I know I can do a #pragma to disable the warning, but I'd like to know the reason for these warnings.

Answer 1

The reason is that boost doesn't push/pop these pragmas in every file that needs data to be packed. They #include a separate file which does the push (abi_prefix.hpp), and then another (abo_suffix.hp) afterwards which does the pop.

That allows them to reuse the same #pragma pack code everywhere, which is handy as it may vary between compilers.

It's perfectly safe though. The #pragma push is followed by a pop, it's just included from a different file. So you should probably just disable that error.

Answer 2

Yes, you'd get that from the #pragma pack directive in config/abi/msvc_prefix.hpp. It indicates that your project's default packing is not 8. That's pretty unusual, is this intentional? Bugs due to packing differences can be a bit tricky to diagnose.

Answer 3

I found a way to get rid of this warning.

You need to edit the file boost_1_**\boost\config\user.hpp and uncomment the line with BOOST_DISABLE_ABI_HEADERS

So you should be defining in this file:

#define BOOST_DISABLE_ABI_HEADERS

Once that is done, just build with bjam like you normally would.

Please see comments below for dangers of this solution