Qt dll build and link

readme.md

This demo is a merge of two dll examples.

https://wiki.qt.io/How_to_create_a_library_with_Qt_and_use_it_in_an_application

http://www.mingw.org/wiki/sampledll

https://wiki.qt.io/How_to_link_to_a_dll

To do this in Windows with MinGW w64... get your qt + mingw setup using the following:

msys2 Install

http://www.msys2.org/ get the version with x86_64 in the installer name.

Follow pacman instructions here: https://wiki.qt.io/MinGW-64-bit

pacman -Sy
pacman -S bash pacman pacman-mirrors msys2-runtime
# may have to close the msys2 window here if there is a warning that says to do so
pacman -Su

pacman -S base-devel git mercurial cvs wget p7zip
pacman -S perl ruby python2 mingw-w64-x86_64-toolchain # mingw-w64-i686-toolchain
pacman -S mingw-w64-x86_64-qt-creator
pacman -S mingw-w64-x86_64-qt5-static

example_dll.cpp

#include <stdio.h>
#include "example_dll.h"

__stdcall void hello(const char *s)
{
        printf("Hello %s\n", s);
}
int Double(int x)
{
        return 2 * x;
}
void CppFunc(void)
{
        puts("CppFunc");
}
void MyClass::func(void)
{
        puts("MyClass.func()");
}

example_dll.h

#ifndef EXAMPLE_DLL_H
#define EXAMPLE_DLL_H

#ifdef __cplusplus
extern "C" {
#endif

#ifdef BUILDING_EXAMPLE_DLL
#define EXAMPLE_DLL __declspec(dllexport)
#else
#define EXAMPLE_DLL __declspec(dllimport)
#endif

void __stdcall EXAMPLE_DLL hello(const char *s);

int EXAMPLE_DLL Double(int x);

#ifdef __cplusplus
}
#endif

// NOTE: this function is not declared extern "C"
void EXAMPLE_DLL CppFunc(void);

// NOTE: this class must not be declared extern "C"
class EXAMPLE_DLL MyClass
{
public:
        MyClass() {};
        virtual ~MyClass() {};
        void func(void);
};

#endif  // EXAMPLE_DLL_H

example_dll.pro

TEMPLATE = lib  # This line is very significant
CONFIG += console c++11
CONFIG -= app_bundle
CONFIG -= qt
CONFIG += dll  # This line is very significant
#CONFIG += staticlib

SOURCES += \
    example_dll.cpp

HEADERS += \
    example_dll.h

#QMAKE_LFLAGS += QMAKE_LFLAGS_WINDOWS_DLL
#QMAKE_CXXFLAGS += -fno-builtin

DEFINES += BUILDING_EXAMPLE_DLL

main.cpp

#include <stdio.h>
#include "example_dll.h"
#include <stdio.h>

int main(void)
{
    hello("World");
    printf("%d\n", Double(333));
    CppFunc();

    MyClass a;
    a.func();

    return 0;
}

main2.cpp

// Dynamic Linking, does not need to be the same compiler, but does need to be the same bit type
// No LIBS required in .pro file, but the INCLUDEPATHS directory should be there.

#include <stdio.h>
#include "example_dll.h"
#include <stdio.h>
#include "windows.h"

#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* hello_ptr) (char *);
typedef int (DLL_CALL_CONVEN* Double_ptr) (int);

#ifdef __cplusplus
}
#endif

int main(void)
{

    HINSTANCE handle = LoadLibrary(TEXT("C:\\development\\build-example_dll-Qt_5_11_2_MinGW_8_2-Release\\release\\example_dll.dll"));

    if (handle == NULL) return 1;

    hello_ptr hello = (hello_ptr) GetProcAddress(handle, "hello");
    Double_ptr Double = (Double_ptr) GetProcAddress(handle, "Double");
    hello("World");
    printf("%d\n", Double(333));
//    CppFunc();

//    MyClass a;
//    a.func();

//    double x = sqrt(2.0);
//    printf ("The sqrt of 2 is: %f\n", x);

    return 0;
}

uses_dll.pro

TEMPLATE = app
CONFIG += console c++11
CONFIG -= app_bundle
CONFIG -= qt

SOURCES += \
        main.cpp

#QMAKE_CXXFLAGS += -fno-builtin
#DEFINES -= BUILDING_EXAMPLE_DLL

DEPENDPATH += . "C:/development/example_dll"
INCLUDEPATH += "C:/development/example_dll"

LIBS += "C:/development/build-example_dll-Qt_5_11_2_MinGW_8_2-Release/release/example_dll.dll"
#LIBS += -L"C:/development/build-example_dll-Qt_5_11_2_MinGW_8_2-Release/release" -lexample_dll