Error including dlib library in c++ project - c++

Question

I need to include dlib in a c++ project. I have properly linked the library in my Makefile. Here is the Makefile:
EXE = face_frontalization
OBJ_DIR = bin
CFLAGS = -g -w
# CXXFLAGS = -w -Wall -Wextra -g -std=c++0x
# LDFLAGS = -lSDL2 -lSDL2_image -lSDL2_ttf -lSDL2_mixer -lSDL2_gfx -lm
dummy_build_folder := $(shell mkdir -p $(OBJ_DIR))
# c++ source files of the project
CXXFILES = $(shell find src -type f -name '*.cpp')
CXXOBJ = $(patsubst src/%.cpp,bin/%.o,$(CXXFILES))
INCLUDE = -I/usr/include/dlib-18.18
LIBS = `pkg-config --libs opencv`
CXXFLAGS = `pkg-config --cflags opencv` -w -Wall -Wextra -g -std=c++0x
LDFLAGS = -lcurl
CFLAGS = `pkg-config --cflags opencv` -g -w
MKDIR = mkdir -p
ifdef V
MUTE =
VTAG = -v
else
MUTE = #
endif
###################################################################
# This is a Makefile progress indicator.
# BUILD is initially undefined
ifndef BUILD
# max equals 256 x's
sixteen := x x x x x x x x x x x x x x x x
MAX := $(foreach x,$(sixteen),$(sixteen))
# T estimates how many targets we are building by replacing BUILD with
# a special string
T := $(shell $(MAKE) -nrRf $(firstword $(MAKEFILE_LIST)) $(MAKECMDGOALS) \
BUILD="COUNTTHIS" | grep -c "COUNTTHIS")
# N is the number of pending targets in base 1, well in fact, base x
# :-)
N := $(wordlist 1,$T,$(MAX))
# auto-decrementing counter that returns the number of pending targets
# in base 10
counter = $(words $N)$(eval N := $(wordlist 2,$(words $N),$N))
# BUILD is now defined to show the progress, this also avoids
# redefining T in loop
BUILD = #echo $(counter) of $(T)
endif
###################################################################
# .PHONY: directories all
#
# directories: ${OUT_DIR}
# ${OUT_DIR}:
# ${MKDIR} ${OUT_DIR}
all: $(EXE)
# build successful
$(EXE): $(CXXOBJ)
$(CXX) $(CXXOBJ) -o $(EXE) $(LIBS) $(LDFLAGS)
$(OBJ_DIR)/%.o: src/%.cpp
$(CXX) $(CXXFLAGS) $(INCLUDE) $< -c -o $#
$(BUILD)
$(OBJ_DIR)/%.o: src/%.c
$(CC) $(CFLAGS) $(INCLUDE) $< -c -o $#
run: all
./$(EXE)
clean:
# Cleaning...
-rm -f $(EXE) $(CXXOBJ)
rmdir bin/
I dont know why but its giving errors on compilation. I have compiled the dlib library itself too and the code examples are running as they should.
The error I am getting is:
bin/fatialfeaturedetect.o: In function `fatial_feature_detector()':
/home/playroom/Desktop/face-frontalization/src/fatialfeaturedetect.cpp:20: undefined reference to `dlib::base_window::wait_until_closed() const'
/home/playroom/Desktop/face-frontalization/src/fatialfeaturedetect.cpp:18: undefined reference to `dlib::image_window::~image_window()'
/home/playroom/Desktop/face-frontalization/src/fatialfeaturedetect.cpp:18: undefined reference to `dlib::image_window::~image_window()'
bin/fatialfeaturedetect.o: In function `dlib::get_serialized_frontal_faces()':
/usr/include/dlib-18.18/dlib/image_processing/frontal_face_detector.h:115: undefined reference to `dlib::base64::base64()'
/usr/include/dlib-18.18/dlib/image_processing/frontal_face_detector.h:2358: undefined reference to `dlib::base64::decode(std::istream&, std::ostream&) const'
/usr/include/dlib-18.18/dlib/image_processing/frontal_face_detector.h:2367: undefined reference to `dlib::base64::~base64()'
/usr/include/dlib-18.18/dlib/image_processing/frontal_face_detector.h:2367: undefined reference to `dlib::base64::~base64()'
bin/fatialfeaturedetect.o: In function `dlib_check_consistent_assert_usage':
/usr/include/dlib-18.18/dlib/gui_widgets/../gui_core/../threads/threads_kernel_shared.h:44: undefined reference to `USER_ERROR__missing_dlib_all_source_cpp_file__OR__inconsistent_use_of_DEBUG_or_ENABLE_ASSERTS_preprocessor_directives_'
bin/fatialfeaturedetect.o: In function `dlib::drawable_window::drawable_window(bool, bool)':
/usr/include/dlib-18.18/dlib/gui_widgets/drawable.h:79: undefined reference to `dlib::base_window::base_window(bool, bool)'
/usr/include/dlib-18.18/dlib/gui_widgets/drawable.h:79: undefined reference to `vtable for dlib::drawable_window'
/usr/include/dlib-18.18/dlib/gui_widgets/drawable.h:79: undefined reference to `dlib::base_window::~base_window()'
bin/fatialfeaturedetect.o: In function `dlib::drawable_window::~drawable_window()':
/usr/include/dlib-18.18/dlib/gui_widgets/drawable.h:195: undefined reference to `vtable for dlib::drawable_window'
/usr/include/dlib-18.18/dlib/gui_widgets/drawable.h:195: undefined reference to `dlib::base_window::close_window()'
/usr/include/dlib-18.18/dlib/gui_widgets/drawable.h:195: undefined reference to `dlib::base_window::~base_window()'
bin/fatialfeaturedetect.o: In function `dlib::scrollable_region_style_default::draw_scrollable_region_border(dlib::canvas const&, dlib::rectangle const&, bool) const':
/usr/include/dlib-18.18/dlib/gui_widgets/style.h:527: undefined reference to `dlib::draw_sunken_rectangle(dlib::canvas const&, dlib::rectangle const&, unsigned char)'
bin/fatialfeaturedetect.o: In function `dlib::image_display::disable_overlay_editing()':
/usr/include/dlib-18.18/dlib/gui_widgets/widgets.h:3485: undefined reference to `dlib::base_window::invalidate_rectangle(dlib::rectangle const&)'
bin/fatialfeaturedetect.o: In function `dlib::compress_stream_kernel_1<dlib::entropy_encoder_model_kernel_5<257ul, dlib::entropy_encoder_kernel_2, 200000ul, 4ul>, dlib::entropy_decoder_model_kernel_5<257ul, dlib::entropy_decoder_kernel_2, 200000ul, 4ul>, dlib::crc32>::decompress(std::istream&, std::ostream&) const':
/usr/include/dlib-18.18/dlib/image_processing/../compress_stream/compress_stream_kernel_1.h:180: undefined reference to `dlib::entropy_decoder_kernel_2::entropy_decoder_kernel_2()'
/usr/include/dlib-18.18/dlib/image_processing/../compress_stream/compress_stream_kernel_1.h:181: undefined reference to `dlib::entropy_decoder_kernel_2::set_stream(std::istream&)'
/usr/include/dlib-18.18/dlib/image_processing/../compress_stream/compress_stream_kernel_1.h:196: undefined reference to `dlib::entropy_decoder_kernel_2::get_target(unsigned int)'
/usr/include/dlib-18.18/dlib/image_processing/../compress_stream/compress_stream_kernel_1.h:201: undefined reference to `dlib::entropy_decoder_kernel_2::decode(unsigned int, unsigned int)'
/usr/include/dlib-18.18/dlib/image_processing/../compress_stream/compress_stream_kernel_1.h:243: undefined reference to `dlib::entropy_decoder_kernel_2::~entropy_decoder_kernel_2()'
/usr/include/dlib-18.18/dlib/image_processing/../compress_stream/compress_stream_kernel_1.h:243: undefined reference to `dlib::entropy_decoder_kernel_2::~entropy_decoder_kernel_2()'
bin/fatialfeaturedetect.o: In function `void dlib::image_window::add_overlay<dlib::rgb_pixel>(std::vector<dlib::rectangle, std::allocator<dlib::rectangle> > const&, dlib::rgb_pixel)':
/usr/include/dlib-18.18/dlib/gui_widgets/widgets.h:3968: undefined reference to `dlib::image_window::add_overlay(std::vector<dlib::image_display::overlay_rect, std::allocator<dlib::image_display::overlay_rect> > const&)'
bin/fatialfeaturedetect.o: In function `dlib::image_window::image_window<dlib::array2d<dlib::rgb_pixel, dlib::memory_manager_stateless_kernel_1<char> > >(dlib::array2d<dlib::rgb_pixel, dlib::memory_manager_stateless_kernel_1<char> > const&)':
/usr/include/dlib-18.18/dlib/gui_widgets/widgets.h:3883: undefined reference to `vtable for dlib::image_window'
/usr/include/dlib-18.18/dlib/gui_widgets/widgets.h:3883: undefined reference to `dlib::image_display::image_display(dlib::drawable_window&)'
/usr/include/dlib-18.18/dlib/gui_widgets/widgets.h:3885: undefined reference to `dlib::image_window::on_image_clicked(dlib::vector<long, 2l> const&, bool, unsigned long)'
/usr/include/dlib-18.18/dlib/gui_widgets/widgets.h:3888: undefined reference to `dlib::base_window::show()'
/usr/include/dlib-18.18/dlib/gui_widgets/widgets.h:3883: undefined reference to `dlib::image_display::~image_display()'
bin/fatialfeaturedetect.o: In function `dlib::entropy_decoder_model_kernel_5<257ul, dlib::entropy_decoder_kernel_2, 200000ul, 4ul>::decode(unsigned long&)':
/usr/include/dlib-18.18/dlib/image_processing/../entropy_decoder_model/entropy_decoder_model_kernel_5.h:422: undefined reference to `dlib::entropy_decoder_kernel_2::get_target(unsigned int)'
/usr/include/dlib-18.18/dlib/image_processing/../entropy_decoder_model/entropy_decoder_model_kernel_5.h:456: undefined reference to `dlib::entropy_decoder_kernel_2::decode(unsigned int, unsigned int)'
/usr/include/dlib-18.18/dlib/image_processing/../entropy_decoder_model/entropy_decoder_model_kernel_5.h:503: undefined reference to `dlib::entropy_decoder_kernel_2::decode(unsigned int, unsigned int)'
/usr/include/dlib-18.18/dlib/image_processing/../entropy_decoder_model/entropy_decoder_model_kernel_5.h:551: undefined reference to `dlib::entropy_decoder_kernel_2::get_target(unsigned int)'
/usr/include/dlib-18.18/dlib/image_processing/../entropy_decoder_model/entropy_decoder_model_kernel_5.h:553: undefined reference to `dlib::entropy_decoder_kernel_2::decode(unsigned int, unsigned int)'
bin/fatialfeaturedetect.o: In function `void dlib::image_window::set_image<dlib::array2d<dlib::rgb_pixel, dlib::memory_manager_stateless_kernel_1<char> > >(dlib::array2d<dlib::rgb_pixel, dlib::memory_manager_stateless_kernel_1<char> > const&)':
/usr/include/dlib-18.18/dlib/gui_widgets/widgets.h:3930: undefined reference to `dlib::image_display::get_image_display_rect() const'
/usr/include/dlib-18.18/dlib/gui_widgets/widgets.h:3934: undefined reference to `dlib::base_window::set_size(int, int)'
bin/fatialfeaturedetect.o: In function `void dlib::load_dng<dlib::array2d<dlib::rgb_pixel, dlib::memory_manager_stateless_kernel_1<char> > >(dlib::array2d<dlib::rgb_pixel, dlib::memory_manager_stateless_kernel_1<char> >&, std::istream&)':
/usr/include/dlib-18.18/dlib/image_loader/image_loader.h:585: undefined reference to `dlib::entropy_decoder_kernel_2::entropy_decoder_kernel_2()'
/usr/include/dlib-18.18/dlib/image_loader/image_loader.h:586: undefined reference to `dlib::entropy_decoder_kernel_2::set_stream(std::istream&)'
/usr/include/dlib-18.18/dlib/image_loader/image_loader.h:757: undefined reference to `dlib::entropy_decoder_kernel_2::~entropy_decoder_kernel_2()'
/usr/include/dlib-18.18/dlib/image_loader/image_loader.h:771: undefined reference to `dlib::entropy_decoder_kernel_2::entropy_decoder_kernel_2()'
/usr/include/dlib-18.18/dlib/image_loader/image_loader.h:772: undefined reference to `dlib::entropy_decoder_kernel_2::set_stream(std::istream&)'
/usr/include/dlib-18.18/dlib/image_loader/image_loader.h:771: undefined reference to `dlib::entropy_decoder_kernel_2::~entropy_decoder_kernel_2()'
/usr/include/dlib-18.18/dlib/image_loader/image_loader.h:757: undefined reference to `dlib::entropy_decoder_kernel_2::~entropy_decoder_kernel_2()'
/usr/include/dlib-18.18/dlib/image_loader/image_loader.h:771: undefined reference to `dlib::entropy_decoder_kernel_2::~entropy_decoder_kernel_2()'
bin/fatialfeaturedetect.o: In function `void dlib::image_display::set_image<dlib::array2d<dlib::rgb_pixel, dlib::memory_manager_stateless_kernel_1<char> > >(dlib::array2d<dlib::rgb_pixel, dlib::memory_manager_stateless_kernel_1<char> > const&)':
/usr/include/dlib-18.18/dlib/gui_widgets/widgets.h:3272: undefined reference to `dlib::scrollable_region::set_total_rect_size(unsigned long, unsigned long)'
/usr/include/dlib-18.18/dlib/gui_widgets/widgets.h:3274: undefined reference to `dlib::scrollable_region::set_total_rect_size(unsigned long, unsigned long)'
/usr/include/dlib-18.18/dlib/gui_widgets/widgets.h:3278: undefined reference to `dlib::base_window::invalidate_rectangle(dlib::rectangle const&)'
/usr/include/dlib-18.18/dlib/gui_widgets/widgets.h:3283: undefined reference to `dlib::popup_menu_region::disable()'
bin/fatialfeaturedetect.o: In function `dlib::entropy_decoder_model_kernel_5<256ul, dlib::entropy_decoder_kernel_2, 200000ul, 4ul>::decode(unsigned long&)':
/usr/include/dlib-18.18/dlib/image_processing/../entropy_decoder_model/entropy_decoder_model_kernel_5.h:422: undefined reference to `dlib::entropy_decoder_kernel_2::get_target(unsigned int)'
/usr/include/dlib-18.18/dlib/image_processing/../entropy_decoder_model/entropy_decoder_model_kernel_5.h:456: undefined reference to `dlib::entropy_decoder_kernel_2::decode(unsigned int, unsigned int)'
/usr/include/dlib-18.18/dlib/image_processing/../entropy_decoder_model/entropy_decoder_model_kernel_5.h:503: undefined reference to `dlib::entropy_decoder_kernel_2::decode(unsigned int, unsigned int)'
/usr/include/dlib-18.18/dlib/image_processing/../entropy_decoder_model/entropy_decoder_model_kernel_5.h:551: undefined reference to `dlib::entropy_decoder_kernel_2::get_target(unsigned int)'
/usr/include/dlib-18.18/dlib/image_processing/../entropy_decoder_model/entropy_decoder_model_kernel_5.h:553: undefined reference to `dlib::entropy_decoder_kernel_2::decode(unsigned int, unsigned int)'
bin/fatialfeaturedetect.o: In function `dlib::entropy_decoder_model_kernel_4<256ul, dlib::entropy_decoder_kernel_2, 200000ul, 4ul>::decode(unsigned long&)':
/usr/include/dlib-18.18/dlib/image_processing/../entropy_decoder_model/entropy_decoder_model_kernel_4.h:348: undefined reference to `dlib::entropy_decoder_kernel_2::get_target(unsigned int)'
/usr/include/dlib-18.18/dlib/image_processing/../entropy_decoder_model/entropy_decoder_model_kernel_4.h:376: undefined reference to `dlib::entropy_decoder_kernel_2::decode(unsigned int, unsigned int)'
/usr/include/dlib-18.18/dlib/image_processing/../entropy_decoder_model/entropy_decoder_model_kernel_4.h:422: undefined reference to `dlib::entropy_decoder_kernel_2::decode(unsigned int, unsigned int)'
/usr/include/dlib-18.18/dlib/image_processing/../entropy_decoder_model/entropy_decoder_model_kernel_4.h:469: undefined reference to `dlib::entropy_decoder_kernel_2::get_target(unsigned int)'
/usr/include/dlib-18.18/dlib/image_processing/../entropy_decoder_model/entropy_decoder_model_kernel_4.h:471: undefined reference to `dlib::entropy_decoder_kernel_2::decode(unsigned int, unsigned int)'
collect2: error: ld returned 1 exit status
make: *** [face_frontalization] Error 1
I cant figure out what I have done in linking the library to the project. Please help.

Answer 1

Dlib is partially header-based and some functions need to have libdlib.a linked to a project
You have two ways how to solve your problem:
link to dlib: LDFLAGS = -ldlib (dlib should be installed or its path provided to linker)
add dlib/all/source.cpp to your project sources list(CXXFILES)

Answer 2

If this error is present during compilation with dLib:
/usr/bin/ld: /tmp/ccps6CPH.o: undefined reference to symbol 'pthread_create##GLIBC_2.2.5'
//lib/x86_64-linux-gnu/libpthread.so.0: error adding symbols: DSO missing from command line
collect2: error: ld returned 1 exit status make: *** [face_frontalization] Error 1
There is a good probability that X11 is missing. I dont know what it is so if somebody does, please tell me. Solution is to just add -lX11 to the LDFLAGS in order to link with it. If you dont want it, you can also specify compiler option -DDLIB_NO_GUI_SUPPORT.
(NOTE: I haven't tested it and dont know what X11 does so better include it than exclude it.)