undefined reference to lodepng::decode

[dumpinfo]

when do the command to compile "make config=debug64"
there occur the error as below, how to fix the it?

/usr/include/c++/5/backward/binders.h:108:11: note: declared here
class binder1st
^
../x64/Debug/libdeepLocoRender.a(TextureDesc.o): In function cTextureDesc::cTextureDesc(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, bool)': /disk4/graphdev/RlRobSim/Test/DeepLoco-0.81/gmake/../render/TextureDesc.cpp:74: undefined reference to lodepng::decode(std::vector<unsigned char, std::allocator >&, unsigned int&, unsigned int&, std::__cxx11::basic_string<char, std::char_traits, std::allocator > const&, LodePNGColorType, unsigned int)'
collect2: error: ld returned 1 exit status
DeepLoco.make:129: recipe for target '../x64/Debug/DeepLoco' failed
make[1]: *** [../x64/Debug/DeepLoco] Error 1
Makefile:16: recipe for target 'DeepLoco' failed
make: *** [DeepLoco] Error 2
make: *** Waiting for unfinished jobs....
Linking DeepLoco_Optimizer

[Neo-X]

Where did you unpack the external libraries? Are they in a folder named external?

[dumpinfo]

thanks, I solve the problem by using the specific version of bullet & caffe provided in the external fold other than check out them from git.