It is wrong to compile box2d on Mac.

[liudb5]

cd box2d && CXXFLAGS=" -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS11.4.sdk -arch armv7 -miphoneos-version-min=6.0 -mcpu=cortex-a8 -I/Users/liudb/GitHub/cocos2d-x-3rd-party-libs-src/contrib/install-ios/armv7/include -O3 -DNDEBUG -std=c++11" CFLAGS=" -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS11.4.sdk -arch armv7 -miphoneos-version-min=6.0 -mcpu=cortex-a8 -I/Users/liudb/GitHub/cocos2d-x-3rd-party-libs-src/contrib/install-ios/armv7/include -O3 -DNDEBUG " cmake . -DCMAKE_TOOLCHAIN_FILE=/Users/liudb/GitHub/cocos2d-x-3rd-party-libs-src/contrib/ios-armv7/toolchain.cmake -DCMAKE_INSTALL_PREFIX=/Users/liudb/GitHub/cocos2d-x-3rd-party-libs-src/contrib/install-ios/armv7 -- Configuring done -- Generating done -- Build files have been written to: /Users/liudb/GitHub/cocos2d-x-3rd-party-libs-src/contrib/ios-armv7/box2d cd box2d && /Applications/Xcode.app/Contents/Developer/usr/bin/make [ 2%] Building CXX object CMakeFiles/box2d.dir/Box2D/Box2D/Collision/Shapes/b2ChainShape.cpp.o In file included from /Users/liudb/GitHub/cocos2d-x-3rd-party-libs-src/contrib/ios-armv7/box2d/Box2D/Box2D/Collision/Shapes/b2ChainShape.cpp:19: /Users/liudb/GitHub/cocos2d-x-3rd-party-libs-src/contrib/ios-armv7/box2d/Box2D/Box2D/Collision/Shapes/b2ChainShape.h:62:52: warning: 'override' keyword is a C++11 extension [-Wc++11-extensions] b2Shape Clone(b2BlockAllocator allocator) const override; ^ /Users/liudb/GitHub/cocos2d-x-3rd-party-libs-src/contrib/ios-armv7/box2d/Box2D/Box2D/Collision/Shapes/b2ChainShape.h:65:30: warning: 'override' keyword is a C++11 extension [-Wc++11-extensions] int32 GetChildCount() const override; ^ /Users/liudb/GitHub/cocos2d-x-3rd-party-libs-src/contrib/ios-armv7/box2d/Box2D/Box2D/Collision/Shapes/b2ChainShape.h:72:70: warning: 'override' keyword is a C++11 extension [-Wc++11-extensions] bool TestPoint(const b2Transform& transform, const b2Vec2& p) const override; ^ /Users/liudb/GitHub/cocos2d-x-3rd-party-libs-src/contrib/ios-armv7/box2d/Box2D/Box2D/Collision/Shapes/b2ChainShape.h:76:60: warning: 'override' keyword is a C++11 extension [-Wc++11-extensions] const b2Transform& transform, int32 childIndex) const override; ^ /Users/liudb/GitHub/cocos2d-x-3rd-party-libs-src/contrib/ios-armv7/box2d/Box2D/Box2D/Collision/Shapes/b2ChainShape.h:79:87: warning: 'override' keyword is a C++11 extension [-Wc++11-extensions] void ComputeAABB(b2AABB aabb, const b2Transform& transform, int32 childIndex) const override; ^ /Users/liudb/GitHub/cocos2d-x-3rd-party-libs-src/contrib/ios-armv7/box2d/Box2D/Box2D/Collision/Shapes/b2ChainShape.h:83:64: warning: 'override' keyword is a C++11 extension [-Wc++11-extensions] void ComputeMass(b2MassData massData, float32 density) const override; ^ /Users/liudb/GitHub/cocos2d-x-3rd-party-libs-src/contrib/ios-armv7/box2d/Box2D/Box2D/Collision/Shapes/b2ChainShape.h:99:15: error: use of undeclared identifier 'nullptr' m_vertices = nullptr; ^ In file included from /Users/liudb/GitHub/cocos2d-x-3rd-party-libs-src/contrib/ios-armv7/box2d/Box2D/Box2D/Collision/Shapes/b2ChainShape.cpp:20: /Users/liudb/GitHub/cocos2d-x-3rd-party-libs-src/contrib/ios-armv7/box2d/Box2D/Box2D/Collision/Shapes/b2EdgeShape.h:36:52: warning: 'override' keyword is a C++11 extension [-Wc++11-extensions] b2Shape Clone(b2BlockAllocator allocator) const override; ^ /Users/liudb/GitHub/cocos2d-x-3rd-party-libs-src/contrib/ios-armv7/box2d/Box2D/Box2D/Collision/Shapes/b2EdgeShape.h:39:30: warning: 'override' keyword is a C++11 extension [-Wc++11-extensions] int32 GetChildCount() const override; ^ /Users/liudb/GitHub/cocos2d-x-3rd-party-libs-src/contrib/ios-armv7/box2d/Box2D/Box2D/Collision/Shapes/b2EdgeShape.h:42:70: warning: 'override' keyword is a C++11 extension [-Wc++11-extensions] bool TestPoint(const b2Transform& transform, const b2Vec2& p) const override; ^ /Users/liudb/GitHub/cocos2d-x-3rd-party-libs-src/contrib/ios-armv7/box2d/Box2D/Box2D/Collision/Shapes/b2EdgeShape.h:46:59: warning: 'override' keyword is a C++11 extension [-Wc++11-extensions] const b2Transform& transform, int32 childIndex) const override; ^ /Users/liudb/GitHub/cocos2d-x-3rd-party-libs-src/contrib/ios-armv7/box2d/Box2D/Box2D/Collision/Shapes/b2EdgeShape.h:49:87: warning: 'override' keyword is a C++11 extension [-Wc++11-extensions] void ComputeAABB(b2AABB aabb, const b2Transform& transform, int32 childIndex) const override; ^ /Users/liudb/GitHub/cocos2d-x-3rd-party-libs-src/contrib/ios-armv7/box2d/Box2D/Box2D/Collision/Shapes/b2EdgeShape.h:52:64: warning: 'override' keyword is a C++11 extension [-Wc++11-extensions] void ComputeMass(b2MassData massData, float32 density) const override; ^ /Users/liudb/GitHub/cocos2d-x-3rd-party-libs-src/contrib/ios-armv7/box2d/Box2D/Box2D/Collision/Shapes/b2ChainShape.cpp:32:15: error: use of undeclared identifier 'nullptr' m_vertices = nullptr; ^ 12 warnings and 2 errors generated. make[3]: [CMakeFiles/box2d.dir/Box2D/Box2D/Collision/Shapes/b2ChainShape.cpp.o] Error 1 make[2]: [CMakeFiles/box2d.dir/all] Error 2 make[1]: [all] Error 2 make: [.box2d] Error 2