undefined refrence link error static library cross compiling for beagle bone black

Question

Cross compiling for Beagle Bone Black on my centos machine.

Im creating an application 'BasicComponentsTest.cpp' which uses the 'SimFrameProducer' class that I've created and built into a static library ie 'libspu.a'. see below makefile and code for reference.

I get link error when compiling the main application using the 'libspu.a' statically link a library, however it works fine when I link the objects directly (see direct object makefile) ie it only fails when compiling with the static library that I created, obviously the the SPU object compile fine and creates the static library file 'libspu.a'.

The only thing I can think that might be wrong is the 'ar' command does not work properly for cross compiled objects, is this correct? is there any other reason why I get this error? BTW I'm still new to c++.

[root@CVDEV SPU]# make
make: Warning: File `Makefile' has modification time 3.6e+04 s in the future
/opt/gcc-linaro-arm-linux-gnueabihf-4.8-2014.04_linux/bin/arm-linux-gnueabihf-g++ -Wall -I ../../SPU/Include -L ../../SPU -lspu BasicComponentsTest.cpp -o Test1
/tmp/cc6Ck7Xj.o: In function `main':
BasicComponentsTest.cpp:(.text+0x1e): undefined reference to `SimFrameProducer::SimFrameProducer(char*)'
collect2: error: ld returned 1 exit status
make: *** [all] Error 1
[root@CVDEV SPU]#

BasicCompontentsTest.cpp main application file

#include <cstdlib>
#include "SimFrameProducer.h"
using namespace std;

/*
 * 
 */
int main(int argc, char** argv) {
    SimFrameProducer* prod = new SimFrameProducer((char*)"Test1");

    prod->Start();
    prod->Stop();

    delete prod;

    return 0;
}

SimFrameProducer.h

#include "SPUBase.h"
#include "SPUFrameProducer.h"

class SimFrameProducer:public SPUFrameProducer, public SPUBase {
public:
    SimFrameProducer(char* instanceId);
    virtual ~SimFrameProducer();
    void Start();
    void Stop();
private:

};

SimFrameProducer.cpp

#include "SimFrameProducer.h"
#include "Include/SimFrameProducer.h"


SimFrameProducer::SimFrameProducer(char* instanceId):SPUBase((char*)"TYPE_SAMPLE", instanceId) {

}

void SimFrameProducer::Start(){

}

void SimFrameProducer::Stop(){

}

SimFrameProducer::~SimFrameProducer() {

}

Makefile main BasicComponentsTest application

CC=/opt/gcc-linaro-arm-linux-gnueabihf-4.8-2014.04_linux/bin/arm-linux-gnueabihf-g++
SPU_PATH=../../SPU
INC=-I $(SPU_PATH)/Include
LIB=-L $(SPU_PATH)

all: 
    $(CC) -Wall $(INC) $(LIB) -lspu BasicComponentsTest.cpp -o Test1

Makefile linking direct object instead of static library

CC=/opt/gcc-linaro-arm-linux-gnueabihf-4.8-2014.04_linux/bin/arm-linux-gnueabihf-g++
SPU_PATH=../../SPU
INC=-I $(SPU_PATH)/Include
LIB=-L $(SPU_PATH)

OBJS=$(SPU_PATH)/SPUBase.o \
$(SPU_PATH)/SPUFrame.o \
$(SPU_PATH)/SPUFrameProducer.o \
$(SPU_PATH)/FFTFrameProducer.o \
$(SPU_PATH)/SimFrameProducer.o

## Target: all
all: 
    $(CC) -Wall $(INC) $(OBJS) BasicComponentsTest.cpp -o Test1

Makefile for SPU lib

CC=/opt/gcc-linaro-arm-linux-gnueabihf-4.8-2014.04_linux/bin/arm-linux-gnueabihf-g++
INC=-I Include
## Target: all
all: 
    $(CC) -Wall $(INC) -c SPUBase.cpp
    $(CC) -Wall $(INC) -c SPUFrame.cpp
    $(CC) -Wall $(INC) -c SPUFrameProducer.cpp
    $(CC) -Wall $(INC) -c FFTFrameProducer.cpp
    $(CC) -Wall $(INC) -c SimFrameProducer.cpp
    ar cr libspu.a SPUBase.o SPUFrame.o SPUFrameProducer.o FFTFrameProducer.o SimFrameProducer.o  

Answer 1

Your archive lacks an object-file index . The ar command line should be:

ar rcs libspu.a SPUBase.o SPUFrame.o SPUFrameProducer.o FFTFrameProducer.o SimFrameProducer.o

You were missing the s option, making your archive just a collection of files in a file (an archive - ar is not just for libraries - though that is invariably what it is used for) rather than a library .

Answer 2

Found the problem it was the order of where I put the static library when building it, apparently the static library was excluded because it was perceived by the compiler as not used, when you put it after the c++ file it realizes that it needs it and uses it. All credits to this post

c++ undefined references with static library

Changed my code to the following to get it to work

$(CC) -Wall -o Test1 $(INC) $(LIB)  BasicComponentsTest.cpp -lspu