CMake "undefined reference to function"

Question

I am attempting to use CMake to link a library(BNO055 Driver). Since the BNO055 Driver doesn't use CMake and it hasn't been changed for about a year I decided to just download the source files and put them in my project.

I then use CMake to create a library and link it.

The issue is that the link does not seem to be working. When I compile the project I get a undefined reference to <function> error, where <function> is a function defined by the BNO055 driver.

Am I creating or linking the library incorrectly?
Do I need to do something else to define these functions?

For the sake of not pasting in 200 lines of code, here is a simplified main.cpp that produces the same error as the real main.cpp. If you would like to see the real main.cpp follow the link bellow to the Github repo

#include "bno055.h"
#include "mraa.hpp"

struct bno055_t bno055;
mraa::I2c *i2c(0);

int main() {
    bno055_init(&bno055);
    i2c->address(0x29);
}

CMakeLists.txt

cmake_minimum_required(VERSION 2.8.4)
project(imc-server)

# CMake
# -- Config
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11 -pthread")

# Global
# -- Include
include(ExternalProject)

# BNO055
# -- Include
include_directories(${CMAKE_SOURCE_DIR}/bno055)

set(SOURCE_FILES ${SOURCE_FILES}
        ${CMAKE_SOURCE_DIR}/bno055/bno055.h
        ${CMAKE_SOURCE_DIR}/bno055/bno055.c)

# MRAA
# -- Build
externalProject_add(mraa
        GIT_REPOSITORY https://github.com/intel-iot-devkit/mraa.git
        GIT_TAG        v0.7.5
)

# Compile
# -- Source
set(SOURCE_FILES ${SOURCE_FILES}
        main.cpp)

# -- Create
add_executable(imc-server ${SOURCE_FILES})
add_dependencies(imc-server mraa)

Relevant Part of Build Log

[ 90%] Linking CXX executable imc-server
CMakeFiles/imc-server.dir/test.cpp.o: In function `main':
/home/noah/Documents/Inertial-Motion-Capture/imc-server/test.cpp:8: undefined reference to `bno055_init(bno055_t*)'
CMakeFiles/imc-server.dir/test.cpp.o: In function `mraa::I2c::address(unsigned char)':
/usr/local/include/mraa/i2c.hpp:99: undefined reference to `mraa_i2c_address'
collect2: error: ld returned 1 exit status
make[2]: *** [imc-server] Error 1
make[1]: *** [CMakeFiles/imc-server.dir/all] Error 2
make: *** [all] Error 2

Project Github(39a6196)
Build Log

You use ${CMAKE_SOURCE_DIR}/bno055/bno055.c file for build bno055 library, so you shouldn't use that file for build imc-server executable. Also, it is better to use library target name for link that executable: target_link_libraries(imc-server bno055). As for external project mraa, you additionally need explicit target dependencies for correctly link with it: add_dependencies(imc-server mraa). — Tsyvarev
– Tsyvarev, Commented Sep 9, 2015 at 22:18
@Tsyvarev Ok, I just added the BNO055 files to the executable(So no lib or linking for bno055). However I am still getting undefined function errors. I also uncommented all the mraa code and I am getting undefined function errors for those functions as well. Is there something I am fundamentally missing here? Commit with changes => 39a6196 — recoup8063
– recoup8063, Commented Sep 9, 2015 at 22:29
Which source is being compiled, when you get error? Precise error message(at least, for one function) would be helpful. — Tsyvarev
– Tsyvarev, Commented Sep 10, 2015 at 9:03
@Tsyvarev Indeed, Here is the end part of the CMake build log. Pastebin — recoup8063
– recoup8063, Commented Sep 10, 2015 at 19:34
As build log shows, function (mraa_i2c_address) is defined in the mraa library, not in the bno055 one. You need both link with that library (target_link_libraries(imc-server libmraa.so) and add dependency with mraa target (add_dependencies(imc-server mraa)). — Tsyvarev
– Tsyvarev, Commented Sep 10, 2015 at 22:07

recoup8063 · Accepted Answer · 2017-05-14 15:10:22Z

15

The problem was that the BNO055 library was written in C, and my program was written in C++.

I learned that to use a function defined in a C program, in a C++ program, you have to wrap the include of the C library in an extern "C" {} block like so:

extern "C" {
    #include "bno055.h"
}
#include "mraa.hpp"

struct bno055_t bno055;
mraa::I2c *i2c(0);

int main() {
    bno055_init(&bno055);
    i2c->address(0x29);
}

answered May 14, 2017 at 15:10

recoup8063

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Comments

Th. Thielemann · Accepted Answer · 2015-10-03 19:57:30Z

0

Remove the header from your SOURCE_FILES.

set(SOURCE_FILES ${SOURCE_FILES}
        # ${CMAKE_SOURCE_DIR}/bno055/bno055.h
        ${CMAKE_SOURCE_DIR}/bno055/bno055.c)

CMake should find the required header by itself. Additional includes are found by include_directories

answered Oct 3, 2015 at 19:57

Th. Thielemann

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2 Comments

recoup8063 Over a year ago

The issue was that I had to wrap the bno055 include in a extern "C" {}"

lelloman Over a year ago

maybe you could post your own answer, it would be more visible

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