Compile *.cpp and *.c with Automake - c++

Question

Structure:
-myProject
-Makefile.am
-configure.ac
-src
-Makefile.am
-main.c
-test.c
-test.h
When I try to compile, I've got the error Undefinded reference to a function from test.c.
Makefile.am:
AUTOMAKE_OPTIONS = foreign
SUBDIRS=src
src/Makefile.am:
bin_PROGRAMS = TEST
AM_CXXFLAGS =-Wall -Wno-psabi -w -pthread -I/usr/local/include
AM_CFLAGS =-Wall -w
#Sources
TEST_SOURCES = test.c main.cpp
TEST_LDADD = #LDFLAGS# -lmosquitto
TEST_LDFLAGS =-lmosquitto
It seem's, that it's not possible to linkt the two sources. Can anybody help me??
ERROR:
make all-recursive
make[1]: Entering directory '/media/sf_Shared/Software/executables/TEST'
Making all in src
make[2]: Entering directory '/media/sf_Shared/Software/executables/TEST/src'
g++ -DHAVE_CONFIG_H -I. -I.. -Wall -Wno-psabi -w -pthread -I/usr/local/include -g -O2 -MT main.o -MD -MP -MF .deps/main.Tpo -c -o main.o main.cpp
mv -f .deps/main.Tpo .deps/main.Po
g++ -Wall -Wno-psabi -w -pthread -I/usr/local/include -g -O2 -lmosquitto -o TEST test.o main.o -lmosquitto
/usr/bin/ld: main.o: in function `main':
/media/sf_Shared/Software/executables/TEST/src/main.cpp:564: undefined reference to `open_ports(unsigned int, unsigned int)'
collect2: error: ld returned 1 exit status
make[2]: *** [Makefile:366: TEST] Error 1
make[2]: Leaving directory '/media/sf_Shared/Software/executables/TEST/src'
make[1]: *** [Makefile:359: all-recursive] Error 1
make[1]: Leaving directory '/media/sf_Shared/Software/executables/TEST'
make: *** [Makefile:300: all] Error 2
I'm including in the main.cpp the test.h. There is the function open_ports declared(u_int32_t open_ports(u_int32_t a, u_int32_t b);), which is implemented in test.c

Answer 1

This is not an automake issue — you are doing the right thing (or at least close to) in the Makefile.am.
The problem is that your symbol is declared without extern "C", but defined only in C, so when the C++ compiler takes your main.cpp, it expects to find a mangled symbols (which encodes the signature of the function, that is the number and types of parameters), rather than a plain (C) one.
You can tell that this is the case because it's looking for open_ports(unsigned int, unsigned int) — rather than just open_ports.
The easiest solution is to change your main.cpp to say:
extern "C" {
#include "test.h"
}
That declares that the test.h header only includes C declarations, which will then generate the right symbol lookup for what you define in test.c.