Getting Multiple Definition error when including a utils file in multiple components

[epdalessandro]

I'm writing a F Prime project that consumes data from multiple sensors that are written in python across TCP sockets, using the built-in F' TCP client component. The parsing of the buffers in each component is very similar, so I wanted to move that functionality to a "utils.cpp" file that I included in the "Components" parent folder.

I added the utils.cpp file to the CMakeLists.txt file in the "Components" folder
set(SOURCE_FILES
"${CMAKE_CURRENT_LIST_DIR}/utils.cpp"
)
and I have include guards in the utils file

#include <vector>
#include <Os/Mutex.hpp>
#ifndef UTILS
#define UTILS

class Lock {
    public:
        Lock(Os::Mutex _mutex) : mutex(_mutex) { mutex.lock(); }
        ~Lock() { mutex.unlock(); }
    private:
        Os::Mutex mutex;
};

uint64_t bytesToUint(const char* bytes, uint16_t len) { // implementation }

std::vector<uint64_t> getDataFromFields(const char* data, std::vector<uint16_t> &sizes) { // implementation }
void ProcessData(uint32_t messageSize, std::vector<char> receivedBytes, std::vector<uint16_t> &fieldSizes, void (*SubsystemDataProcessor) (uint8_t msgType)) { // implementation }

#endif

I'm then including this file in the {ComponentName}.cpp file in multiple components with #include "Components/utils.cpp"

However when I run this I get the following error:

I don't understand why there are multiple definitions if I have include guards, unless it's first linking each of the components so each component thinks that "utils.cpp" hasn't been defined, then defines it and then after each component is linked together and the compiler "finds" the multiple definitions

[LeStarch]

These are linker multiple define errors. The issue is you've defined the functions inside a c++ file that you are treating as a header. You should instead create utils.hpp and utils.cpp the first has definitions and the second has implementation. Then include the utils.hpp in the component not the utils.cpp.

[LeStarch]

Here is a quick refactor that will help:

utils.hpp: has definitions of class Lock and function prototypes.

#include <vector>
#include <Os/Mutex.hpp>
#ifndef UTILS
#define UTILS

class Lock {
    public:
        Lock(Os::Mutex _mutex) : mutex(_mutex) { mutex.lock(); }
        ~Lock() { mutex.unlock(); }
    private:
        Os::Mutex mutex;
};

uint64_t bytesToUint(const char* bytes, uint16_t len);

std::vector<uint64_t> getDataFromFields(const char* data, std::vector<uint16_t> &sizes);
void ProcessData(uint32_t messageSize, std::vector<char> receivedBytes, std::vector<uint16_t> &fieldSizes, void (*SubsystemDataProcessor) (uint8_t msgType));

#endif

utils.cpp: has implementation of functions.

#include <utils.hpp>

uint64_t bytesToUint(const char* bytes, uint16_t len) { // implementation }

std::vector<uint64_t> getDataFromFields(const char* data, std::vector<uint16_t> &sizes) { // implementation }
void ProcessData(uint32_t messageSize, std::vector<char> receivedBytes, std::vector<uint16_t> &fieldSizes, void (*SubsystemDataProcessor) (uint8_t msgType)) { // implementation }

[epdalessandro]

Thank you, that solved the multiple-definition problem, however now when I try to build in the deployment, it cannot find the functions in the utils file:

I have the utils file added to the Components CMakelists:

# Include project-wide components here

set(SOURCE_FILES
  "${CMAKE_CURRENT_LIST_DIR}/utils.cpp"
)

# add_fprime_subdirectory("${CMAKE_CURRENT_LIST_DIR}/GPS/")
# add_fprime_subdirectory("${CMAKE_CURRENT_LIST_DIR}/Radio/")
add_fprime_subdirectory("${CMAKE_CURRENT_LIST_DIR}/EpsManager/")
add_fprime_subdirectory("${CMAKE_CURRENT_LIST_DIR}/AdcsManager/")
add_fprime_subdirectory("${CMAKE_CURRENT_LIST_DIR}/QuadMagManager/")
add_fprime_subdirectory("${CMAKE_CURRENT_LIST_DIR}/OpvManager/")
add_fprime_subdirectory("${CMAKE_CURRENT_LIST_DIR}/GPS/")

A thought we had to fix this was import the file in the CMakeLists for each component, for example:

set(SOURCE_FILES
  "${CMAKE_CURRENT_LIST_DIR}/../utils.cpp"
  "${CMAKE_CURRENT_LIST_DIR}/QuadMagManager.fpp"
  "${CMAKE_CURRENT_LIST_DIR}/QuadMagManager.cpp"
)

But this led to this error where it can't find the Fw namespace, when in the utils file I'm including the ActiveComponent Base:

#include "utils.hpp"
#include "Fw/Comp/ActiveComponentBase.hpp"

[epdalessandro]

The fix to this second problem was to instead create a std::function object that captures both the *this pointer and the SubsystemDataProcessor function, and pass in the NUM_MESSAGE_LENGTH_BYTES/NUM_TYPE_BYTES as parameters