Question

I am likely missing something simple but I can’t really figure it out.

This is from the makefile:

box2d.clean.h:
    cpp -x c++ -DEM_NO_LIBCPP -IBox2D_v2.2.1 root.h > box2d.clean.h

Let’s take a look at root.h:

// Prevent some inclusions
#define NDEBUG

#ifdef EM_NO_LIBCPP
#define _FEATURES_H
#define _GLIBCXX_CMATH
#define _GLIBCXX_CXX_CONFIG_H
#define _CPP_TYPE_TRAITS_H
#define _EXT_TYPE_TRAITS
#define _GLIBCXX_NUMERIC_LIMITS
#define __GNUC_PREREQ(x, y) 0
#define _STL_RELOPS_H
#define _STL_PAIR_H
#define _FUNCTEXCEPT_H
#define _EXT_NUMERIC_TRAITS
#define _STL_ITERATOR_BASE_TYPES_H
#define _STL_ITERATOR_H
#endif

#include <Box2D/Box2D.h>

Okay. Yes I see that we are preventing the inclusion of several headers by defining their include guards. Headers like <Features.h>.

My questions:

What purpose might preventing the inclusion of these headers serve?

What command should cpp be aliased to? On my machine I see this output:

cpp -x c++ -DEM_NO_LIBCPP -IBox2D_v2.2.1 root.h > box2d.clean.h
i686-apple-darwin11-llvm-gcc-4.2: c: No such file or directory
i686-apple-darwin11-llvm-gcc-4.2: c++: No such file or directory
i686-apple-darwin11-llvm-gcc-4.2: warning: '-x -x' after last input file has no effect
i686-apple-darwin11-llvm-gcc-4.2: no input files

Why would gcc be looking for c?

Answer 1

I was able to solve the problem with the cpp command by removing the space between -x and c++.

cpp -xc++ -DEM_NO_LIBCPP -IBox2D_v2.2.1 root.h > box2d.clean.h