"clang: error: linker command failed with exit code 1" on "ld: symbol(s) not found for architecture x86_64"

Right, please bare with on this, it might be quite a long one, and one related issue was solved here (I think): CMake make[2]: *** No rule to make target `/path/to/uthash/utarray.h', needed by `HelloTest'. Stop.

I have been struggling for some days now to build a simple 'Hello World' programme which mixes C and C++, and pulls in various external libraries using CMake. For full disclosure it should be known that I am fairly new to C, C++ and CMake hence please be nice.

I am working in OS X Yosemite 10.10.4 (my googling seems to suggest this might be part of the problem). I am working out of the CLion IDE.

Alas, here we go, here is the programme I am trying to build:

#include <iostream>
#include "Simbody.h" \\Written in C++
extern "C"
{
    #include "project_in_C.h"
}

using namespace std;
using namespace SimTK;

int main(int argc, char** argv) {
    cout << "Hello, World!" << endl;
    return 0;
}

We have a physics library written in C++ a bespoke project written in C, for which the main header file is, lets call it; project_in_C.h.

Again; all I am trying to do is build a simple mixed C/C++ project.

Now, the above is executed using CMake, and the following CMakeLists.txt file:

cmake_minimum_required(VERSION 3.2)
project(HelloTest)

# Simbody
find_package(Simbody REQUIRED)
include_directories(${Simbody_INCLUDE_DIR})
link_directories(${Simbody_LIB_DIR})

# Project C Headers
set(PROJC_ROOT_DIR "/Users/usr/project-c")
set(PROJC_INCLUDE_DIR ${PROJC_ROOT_DIR}/src
                      ${PROJC_ROOT_DIR}/dir1
                      ${PROJC_ROOT_DIR}/dir2)
include_directories(${PROJC_INCLUDE_DIR})

# Check that it has found the most important header
find_path(projFound project_in_C.h PATHS "/Users/usr/project-c/src")
if(NOT projFound)
  message(FATAL_ERROR "Cannot find folder containing project_in_C.h")
endif()

# Project C Source [we want to avoid globbing]
set(PROJC_SOURCE ${PROJC_ROOT_DIR}/src/file1.c
                 ${PROJC_ROOT_DIR}/src/file2.c
                 ${PROJC_ROOT_DIR}/src/file3.c
                 ${PROJC_ROOT_DIR}/src/file4.c
                 ${PROJC_ROOT_DIR}/dir1/file5.c)
# Make library from source files
add_library(PROJC_LIBRARIES ${PROJC_SOURCE})

# Tie together
set(SOURCE_FILES main.cpp)
add_executable(HelloTest ${SOURCE_FILES})
target_link_libraries(HelloTest ${Simbody_LIBRARIES} ${PROJC_LIBRARIES})

So far so good, but here is where the truly mysterious problem arises. Upon build this is what I get in return:

/Applications/http://ift.tt/1Itdw3K --build /Users/usr/Library/Caches/clion10/cmake/generated/c1d0f54d/c1d0f54d/Debug --target all -- -j 2
Scanning dependencies of target HelloTest
[ 91%] Built target PROJC_LIBRARIES
[100%] Building CXX object CMakeFiles/http://ift.tt/1h8dMOb
Linking CXX executable HelloTest
Undefined symbols for architecture x86_64:
  "_program_execution_wrapper", referenced from:
      _main in main.cpp.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make[2]: *** [HelloTest] Error 1
make[1]: *** [CMakeFiles/HelloTest.dir/all] Error 2
make: *** [all] Error 2

But what the flippin' dynamite does that actually mean?

It is kicking up a fuss with project_in_C.h where the section the error seems to be referring to is written as so:

int program_execution_wrapper(int argc, char **argv);

int __program(int argc, char **argv);
#define main main(int argc, char **argv) { return prog_exec_wrap(argc, argv); } int __program

As ever, any help greatly appreciated.

via Chebli Mohamed