undefined reference to sqrt in SVM-Struct (have used -lm)

Question

Actually, I am working with the well-known SVM-struct project ( http://www.cs.cornell.edu/people/tj/svm_light/svm_struct.html )on Ubuntu 16.04. I followed the instructions in http://www.cs.cornell.edu/people/tj/svm_light/svm_multiclass.html to use SVM-multiclass, downloaded the source code and make . But I met some errors when building the project:

$ make
cd svm_light; make svm_learn_hideo_noexe
make[1]: Entering directory '/home/parallels/CLionProjects/svm_multiclass/svm_light'
make[1]: Nothing to be done for 'svm_learn_hideo_noexe'.
make[1]: Leaving directory '/home/parallels/CLionProjects/svm_multiclass/svm_light'
cd svm_struct; make svm_struct_noexe
make[1]: Entering directory '/home/parallels/CLionProjects/svm_multiclass/svm_struct'
make[1]: Nothing to be done for 'svm_struct_noexe'.
make[1]: Leaving directory '/home/parallels/CLionProjects/svm_multiclass/svm_struct'
gcc  -O3 -lm -Wall svm_struct/svm_struct_learn.o svm_struct_learn_custom.o svm_struct_api.o svm_light/svm_hideo.o svm_light/svm_learn.o svm_light/svm_common.o svm_struct/svm_struct_common.o svm_struct/svm_struct_main.o -o svm_multiclass_learn 
svm_light/svm_learn.o: In function `estimate_sphere':
svm_learn.c:(.text+0x6e88): undefined reference to `sqrt'
svm_light/svm_learn.o: In function `estimate_r_delta':
svm_learn.c:(.text+0x7053): undefined reference to `sqrt'
svm_light/svm_learn.o: In function `estimate_r_delta_average':
svm_learn.c:(.text+0x7b04): undefined reference to `sqrt'
svm_light/svm_learn.o: In function `length_of_longest_document_vector':
svm_learn.c:(.text+0x7b86): undefined reference to `sqrt'
svm_light/svm_learn.o: In function `incorporate_unlabeled_examples':
svm_learn.c:(.text+0x89eb): undefined reference to `sqrt'
svm_light/svm_learn.o:svm_learn.c:(.text+0xc952): more undefined references to `sqrt' follow
svm_light/svm_common.o: In function `classify_example':
svm_common.c:(.text+0x38f): undefined reference to `tanh'
svm_common.c:(.text+0x42d): undefined reference to `exp'
svm_common.c:(.text+0x4a7): undefined reference to `pow'
svm_light/svm_common.o: In function `kernel':
svm_common.c:(.text+0x870): undefined reference to `tanh'
svm_common.c:(.text+0x90d): undefined reference to `exp'
svm_common.c:(.text+0x988): undefined reference to `pow'
svm_light/svm_common.o: In function `model_length_s':
svm_common.c:(.text+0x2c8d): undefined reference to `sqrt'
svm_light/svm_common.o: In function `model_length_n':
svm_common.c:(.text+0x2f5c): undefined reference to `sqrt'
svm_light/svm_common.o: In function `cholesky_matrix':
svm_common.c:(.text+0x3c6f): undefined reference to `sqrt'
svm_light/svm_common.o: In function `find_indep_subset_of_matrix':
svm_common.c:(.text+0x3f41): undefined reference to `sqrt'
svm_light/svm_common.o: In function `single_kernel':
svm_common.c:(.text+0xc0c): undefined reference to `tanh'
svm_common.c:(.text+0xc84): undefined reference to `pow'
svm_common.c:(.text+0xcfb): undefined reference to `exp'
collect2: error: ld returned 1 exit status
Makefile:48: recipe for target 'svm_multiclass_learn' failed
make: *** [svm_multiclass_learn] Error 1

I think the Makefile has already included -lm .

# Makefile for SVM-multiclass, 03.07.04

#Use the following to compile under unix or cygwin
CC = gcc
LD = gcc

#Call 'make' using the following line to make CYGWIN produce stand-alone Windows executables
#       make 'SFLAGS=-mno-cygwin'

CFLAGS =   $(SFLAGS) -O3 -fomit-frame-pointer -ffast-math -Wall
LDFLAGS =  $(SFLAGS) -O3 -lm -Wall
#CFLAGS =  $(SFLAGS) -pg -Wall
#LDFLAGS = $(SFLAGS) -pg -lm -Wall 

all: svm_multiclass_learn svm_multiclass_classify

.PHONY: clean
clean: svm_light_clean svm_struct_clean
    rm -f *.o *.tcov *.d core gmon.out *.stackdump 

#-----------------------#
#----   SVM-light   ----#
#-----------------------#
svm_light_hideo_noexe: 
    cd svm_light; make svm_learn_hideo_noexe

svm_light_clean: 
    cd svm_light; make clean

#----------------------#
#----  STRUCT SVM  ----#
#----------------------#

svm_struct_noexe: 
    cd svm_struct; make svm_struct_noexe

svm_struct_clean: 
    cd svm_struct; make clean

#-------------------------#
#----  SVM MULTICLASS ----#
#-------------------------#

svm_multiclass_classify: svm_light_hideo_noexe svm_struct_noexe svm_struct_api.o svm_struct/svm_struct_classify.o svm_struct/svm_struct_common.o svm_struct/svm_struct_main.o 
    $(LD) $(LDFLAGS) svm_struct_api.o svm_struct/svm_struct_classify.o svm_light/svm_common.o svm_struct/svm_struct_common.o -o svm_multiclass_classify $(LIBS)

svm_multiclass_learn: svm_light_hideo_noexe svm_struct_noexe svm_struct_api.o svm_struct_learn_custom.o svm_struct/svm_struct_learn.o svm_struct/svm_struct_common.o svm_struct/svm_struct_main.o
    $(LD) $(LDFLAGS) svm_struct/svm_struct_learn.o svm_struct_learn_custom.o svm_struct_api.o svm_light/svm_hideo.o svm_light/svm_learn.o svm_light/svm_common.o svm_struct/svm_struct_common.o svm_struct/svm_struct_main.o -o svm_multiclass_learn $(LIBS)


svm_struct_api.o: svm_struct_api.c svm_struct_api.h svm_struct_api_types.h svm_struct/svm_struct_common.h
    $(CC) -c $(CFLAGS) svm_struct_api.c -o svm_struct_api.o

svm_struct_learn_custom.o: svm_struct_learn_custom.c svm_struct_api.h svm_light/svm_common.h svm_struct_api_types.h svm_struct/svm_struct_common.h
    $(CC) -c $(CFLAGS) svm_struct_learn_custom.c -o svm_struct_learn_custom.o

Answer 1

The linker collects dependencies first ( svm_light/svm_learn.o ) and fills them in when it sees a definition ( -lm ).

You seem to already have a $(LIBS) at the end of your ld invocation, so just:

LIBS += -lm

should fix it.

Other tips:

• you can replace the pattern cd X; make TARGET cd X; make TARGET with make -CX TARGET
• you can refer to the target as $@ and the first prerequisite in the dependency list as $< , so your last rule can be written as:

svm_struct_learn_custom.o: svm_struct_learn_custom.c svm_struct_api.h svm_light/svm_common.h svm_struct_api_types.h svm_struct/svm_struct_common.h
    $(CC) -c $(CFLAGS) $< -o $@

where the recipe redefinition of the built-in recipe for compiling .c files, so it suffices to simply list the headers as (extra) prerequisites:

svm_struct_learn_custom.o: svm_struct_api.h svm_light/svm_common.h svm_struct_api_types.h svm_struct/svm_struct_common.h