Julia dll cpp dynamic loading

main.cpp

// This (static linking to an archive file) doesn't work because we are using a
// different compiler than the one that built julia!
//#include <julia.h>
//#include <iostream>
//using namespace std;

//int main()//int argc, char *argv[])
//{
//    cout << "Hello World!" << endl;
//    /* required: setup the Julia context */
//    jl_init();

//    /* run Julia commands */
//    jl_eval_string("print(sqrt(2.0))");

//    /* strongly recommended: notify Julia that the
//         program is about to terminate. this allows
//         Julia time to cleanup pending write requests
//         and run all finalizers
//    */
//    jl_atexit_hook(0);
//    return 0;
//}

// Heavily based on https://gist.github.com/GunnarFarneback/df2910fa9460cd267b37416f3efea77b
// See also https://docs.julialang.org/en/v0.6.0/manual/embedding/
#include <iostream>
//#define JULIA_ENABLE_THREADING
#include "windows.h"
#include "julia.h"

// DLL resolution also checks in the PATH environment variable
// https://msdn.microsoft.com/en-us/library/7d83bc18.aspx
#define JULIA_DIR "C:\\Users\\USERNAME\\AppData\\Local\\Julia-0.6.4"

#define DLL_CALL_CONVEN __stdcall

#ifdef __cplusplus
extern "C"
{
#endif

// typedef <return type> (DLL_CALL_CONVEN* <func_name>_ptr)(parameter list);
typedef void (DLL_CALL_CONVEN* jl_init_ptr)();
typedef jl_value_t* (DLL_CALL_CONVEN* jl_eval_string_ptr)(const char *);
typedef void (DLL_CALL_CONVEN* jl_atexit_hook_ptr)(int);

#ifdef __cplusplus
}
#endif

using namespace std;

std::string GetLastErrorAsString();

int main()
{
    cout << "Hello World!" << endl;

     HINSTANCE handle = LoadLibrary(TEXT("libjulia.dll"));  // This works if julia.exe is in the path
//     HINSTANCE handle = LoadLibrary(TEXT(JULIA_DIR "\\bin\\libjulia.dll"));

    if (handle == NULL){
        // Apparently it is not loading when executed inside qtcreator_process_stub
        // But it will load if executed from Windows Explorer
        cerr << "ERROR: Failed to open a handle to the dll" << endl;
        cerr << GetLastErrorAsString() << endl;
        return 1;
    }
    cout << "Library Loaded!" << endl;
    system("pause");

    jl_init_ptr jl_init = (jl_init_ptr)GetProcAddress(handle, "jl_init");
    jl_atexit_hook_ptr jl_atexit_hook = (jl_atexit_hook_ptr)GetProcAddress(handle, "jl_atexit_hook");
    jl_eval_string_ptr jl_eval_string = (jl_eval_string_ptr)GetProcAddress(handle, "jl_eval_string");
    jl_init();
    cout << endl << "print(sqrt(2.0))" << endl;
    jl_eval_string("print(sqrt(2.0))");
    jl_atexit_hook(0);

    cout << endl << "Finished running some julia" << endl;
    system("pause");
    return 0;
}

// https://stackoverflow.com/questions/1387064/how-to-get-the-error-message-from-the-error-code-returned-by-getlasterror
//Returns the last Win32 error, in string format. Returns an empty string if there is no error.
std::string GetLastErrorAsString()
{
    //Get the error message, if any.
    DWORD errorMessageID = ::GetLastError();
    if(errorMessageID == 0)
        return std::string(); //No error message has been recorded

    LPSTR messageBuffer = nullptr;
    size_t size = FormatMessageA(FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS,
                                 NULL, errorMessageID, MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT), (LPSTR)&messageBuffer, 0, NULL);

    std::string message(messageBuffer, size);

    //Free the buffer.
    LocalFree(messageBuffer);

    return message;
}