Undefined reference resulting from g++ linking

Question

Hi there,

I am new to g++ and Makefile. I am trying to link this BeBOP SMC library, which is in my lib directory. Under the lib directory are bebop_util and sparse_matrix_converter, both of which have already been built without errors. I see libbebop_util.a, libbebop_util.so under bebop_util and libsparse_matrix_converter.a, libsparse_matrix_converter.so under sparse_matrix_converter. Below is the source:

Makefile

CC=g++
CFLAGS=-c -Wall

test.out: test.o
    $(CC) -o test.out -Ilib/sparse_matrix_converter/include -Llib/bebop_util \
-Llib/sparse_matrix_converter -lbebop_util -lsparse_matrix_converter test.o

test.o: test.cpp
    $(CC) $(CFLAGS) -Ilib/sparse_matrix_converter/include test.cpp

clean:
    rm -f test.o test.out

---

test.cpp

#include <bebop/smc/sparse_matrix.h>
#include <bebop/smc/sparse_matrix_ops.h>

int main(int argc, const char* argv[])
{
    struct sparse_matrix_t* A = load_sparse_matrix (MATRIX_MARKET, "sample_input");
    destroy_sparse_matrix(A);
    return 0;
}

---

Output:

login3% make
g++ -c -Wall -Ilib/sparse_matrix_converter/include test.cpp
g++ -o test.out -Ilib/sparse_matrix_converter/include -Llib/bebop_util -Llib/sparse_matrix_converter -lbebop_util -lsparse_matrix_converter test.o
test.o: In function `main':
test.cpp:(.text+0x1a): undefined reference to `load_sparse_matrix(sparse_matrix_file_format_t, char const*)'
test.cpp:(.text+0x27): undefined reference to `destroy_sparse_matrix(sparse_matrix_t*)'
collect2: ld returned 1 exit status
make: *** [test.out] Error 1

---

Please note that test.cpp depends on sparse_matrix_converter, which depends on bebop_util. Would you please let me know what mistakes I may have made? Thanks.

Tom

Answer 1

The BeBOP code looks to be C code but hasn't add the correct C++ guards. Surround your includes with extern "C" to fix that:

extern "C" {
#include <bebop/smc/sparse_matrix.h>
#include <bebop/smc/sparse_matrix_ops.h>
}