问题
So I want to publicly expose a Box2D (C++) pointer to other Objective-C++ classes in my cocos2d + box2d project. I declare a method "getWorld" in my interface which references C++ class b2World and imports Box2D.h. All the files in my project are .mm extension, and I get the following compile error:
In file included from DebugDrawLayer.mm:2:
In file included from World.h:10:
In file included from external/Box2d/Box2D/Box2D.h:34:
external/Box2d/Box2D/Common/b2Settings.h:22:10: fatal error: 'cassert' file not found
#include <cassert>
I guess Box2D.h is somehow compiled as C instead of C++, but I fail to understand how this happens. According to the log the include chain clearly starts from a .mm file.
Update:
The log says for World.mm (compiled earlier) that it clearly compiles as objective-c++
CompileC Objects-normal/i386/World.o World.mm normal i386 objective-c++ com.apple.compilers.llvm.clang.1_0.compiler
but for DebugDrawLayer.mm it says objective-c
CompileC Objects-normal/i386/DebugDrawLayer.o DebugDrawLayer.mm normal i386 objective-c com.apple.compilers.llvm.clang.1_0.compiler
Both files are set as default - Objective-C++ source. What gives..?
回答1:
This appears to be a MAJOR bug in Xcode4, nothing to do with compiler settings - just Xcode internals.
UPDATE:
I eventually found the root cause. Yes, it's a bug in Xcode/LLVM. It compiles files in the wrong order, and then overrides its own settings, and breaks itself. Apple's tech support was too incompetent to even understand the problem, so I doubt they'll be fixing the bug anytime soon.
(NB: Skip this section, and see below, for my original answer, that gives a BRUTE FORCE but VERY QUICK TO DO solution)
What happens is ... if the compiler "sees" a C++ header while processing a C class ... it then marks that header (internally) as "C" (even when this is literally impossible).
Later on, when it comes back to that header, trying to compile it with C++, it finds it has already told-itself that the header is "C" (because it's incredibly stupid) ... and promptly crashes.
The correct solution (which requires lots of time and effort) is to go through EVERY C FILE in your project, and check (manually, because Xcode sucks) EVERY reference to EVERY header file -- and, for each one, EVERY header file it imports ... etc.
(this can take hours)
...until you find the chain of imports that leads to a C file "seeing" a C++ header.
All of this should be automated (but isn't). And the root problem shouldn't happen (if Xcode were correctly written).
I tried everything listed elsewhere on the web, most of the solutions are "keep removing/adding the file, and eventually Xcode will fix itself if you're lucky".
I wasn't lucky. The only thing that worked was:
- Go to build settings for your project
- find the "Compile Sources As" setting
- set it to "Objective-C++"
- re-build
The actual name/value is: "GCC_INPUT_FILETYPE = sourcecode.cpp.objcpp" - so my guess is that this sidesteps Xcode's (broken!) internal logic.
回答2:
I had same error and I just renamed one of my class(from which I call my box2d classes) from className.m to className.mm and now it works.
回答3:
Removing DebugDrawLayer from the project and then re-adding it again solved the issue. Maybe there were some strange compiler settings on the file in the build phases settings, never checked those.
回答4:
I had problems with this in my Cocos2D/Box2D project, it wasn't solved until I renamed ALL my .m files in my project (excluding the ones in Cocos2D of course) to .mm to compile them as Objective-C++.
I guess @Adam's solution works too, but I prefer to leave compilation settings as "According to File Type", feels cleaner.
回答5:
Actually correct solution it's take your code into:
#if __cplusplus
// … your code …
#endif // __cplusplus
回答6:
I had this problem when having the #import "Box2D.h" in Prefix.pch. I changed the #import "Box2D.h" to be in each file that uses it instead.
来源：https://stackoverflow.com/questions/12049868/objective-c-importing-c-class-fails-cassert-not-found