Makefile for a c++ code while using Armadillo matrix library

Question

I have installed Armadillo linear algebra library to do some matrix operations on Linux mint OS. but,my bad is,i can't compile and execute my c++ code using makefile:

my makefile is as follows:

CC=g++
all: file_1.o main.o
    $(CC)  -o EXCUTE_ALL file_1.o main.o

main.o: main.cpp file_1.h
    $(CC) -c main.cpp

file_1.o: file_1.h
    $(CC) -c file_1.cpp

#running    
run : 
    ./EXCUTE_ALL

.PHONY: clean   
clean:
    rm -f *.o
    rm -f EXCUTE_ALL

---

file_1.cpp is:

#include <iostream>
#include <stdio.h>
#include "armadillo"
#include "file_1.h"
using namespace std;
using namespace arma;

mat myclass::product(mat my_matrix)
{
    mat product=my_matrix * my_matrix;
    return product;
}

---

file_1.h is:

#include <iostream>
#include <stdio.h>
#include "armadillo"

using namespace std;
using namespace arma;

class myclass{
public:
    mat product(mat matrixAA);
};

---

Main.cpp is:

#include <iostream>
#include <stdio.h>
#include "armadillo"
#include "file_1.h"
using namespace std;
using namespace arma;

int main() 
{
    myclass matfile;
    mat BB;
    mat AA=randu<mat>(500,500);
    BB=matfile.product(AA);
    return 0;
}

---

and get the following error:

file_1.o: In function `void arma::blas::gemv<double>(char const*, int const*, int const*, double const*, double const*, int const*, double const*, int const*, double const*, double*, int const*)':
file_1.cpp:(.text._ZN4arma4blas4gemvIdEEvPKcPKiS5_PKT_S8_S5_S8_S5_S8_PS6_S5_[void arma::blas::gemv<double>(char const*, int const*, int const*, double const*, double const*, int const*, double const*, int const*, double const*, double*, int const*)]+0x53): undefined reference to `wrapper_dgemv_'
file_1.o: In function `void arma::blas::gemm<double>(char const*, char const*, int const*, int const*, int const*, double const*, double const*, int const*, double const*, int const*, double const*, double*, int const*)':
file_1.cpp:(.text._ZN4arma4blas4gemmIdEEvPKcS3_PKiS5_S5_PKT_S8_S5_S8_S5_S8_PS6_S5_[void arma::blas::gemm<double>(char const*, char const*, int const*, int const*, int const*, double const*, double const*, int const*, double const*, int const*, double const*, double*, int const*)]+0x61): undefined reference to `wrapper_dgemm_'
collect2: ld returned 1 exit status
make: *** [all] Error 1

But, this works with out makefile,using the following command:

 `g++ -o obj Main.cpp file_1.cpp -l armadillo`. 

can any one help me please,if i miss something in my makefile. thanks..

Answer 1

Your Makefile is not telling the linker to link it with the Armadillo library. A way to solve it, although I'm not sure if it's the "good practices" way is to add -l armadillo to the end of the "all:" line. It probably will be unable to find "EXCUTE_ALL", as I don't see anything creating it and I see it gets erased after cleaning.