Why qt project can throw errors like undefined reference to `__imp_ Py

I want to add python functions in C code. The project is written using qt.

In Mask.pro I have:

...
INCLUDEPATH  = "D:/workplace/Python/include"
LIBS  = -L"D:/workplace/Python/libs"
...

In main.cpp I have:

#pragma push_macro("slots")
#undef slots
#include <Python.h>
#pragma pop_macro("slots")
...
PyObject *pName, *pModule, *pFunc;
PyObject *pArgs, *pValue;

Py_Initialize();
pName = PyUnicode_DecodeFSDefault("Morpho");

pModule = PyImport_Import(pName);
pFunc = PyObject_GetAttrString(pModule, 0);

Py_XDECREF(pFunc);
Py_DECREF(pModule);
...

Errors while compiling:

D:\workplace\Python\include\object.h:500: ошибка: undefined reference to `_imp___Py_Dealloc'
debug/main.o: In function `Py_DECREF':
D:/workplace/Python/include/object.h:500: undefined reference to `_imp___Py_Dealloc'
C:\Projects\Cproject\QT\Mask\build-Mask-Desktop-Debug\..\Mask\main.cpp:99: ошибка: undefined reference to `_imp__Py_Initialize'
debug/main.o: In function `Z5qMainiPPc':
C:\Projects\Cproject\QT\Mask\build-Mask-Desktop-Debug/../Mask/main.cpp:99: undefined reference to `_imp__Py_Initialize'
C:\Projects\Cproject\QT\Mask\build-Mask-Desktop-Debug\..\Mask\main.cpp:100: ошибка: undefined reference to `_imp__PyUnicode_DecodeFSDefault'
C:\Projects\Cproject\QT\Mask\build-Mask-Desktop-Debug\..\Mask\main.cpp:102: ошибка: undefined reference to `_imp__PyImport_Import'
C:\Projects\Cproject\QT\Mask\build-Mask-Desktop-Debug\..\Mask\main.cpp:103: ошибка: undefined reference to `_imp__PyObject_GetAttrString'

I just can't find what I am doing wrong or what I even could forget about.

CodePudding user response：

You specified where the linker should search for libraries, but you didn't specify which libraries to use. Check [SO]: How to include OpenSSL in Visual Studio (@CristiFati's answer) for more details on building on Win.

Inside Python's lib directory ("D:/workplace/Python/libs" in your case), there should be a file called python${PYTHON_MAJOR}${PYTHON_MINOR}.lib depending on which Python version you are using (e.g. python39.lib for Python 3.9). You need to let the linker know about it:

LIBS  = -L"D:/workplace/Python/libs" -lpython39

Note: On Win you don't have to separately install Python packages (python*, libpython*, libpython*-dev, ...) as they are all contained by the (official) installer.

CodePudding user response：

Whole .pro file:

QT        = core gui

greaterThan(QT_MAJOR_VERSION, 4): QT  = widgets

CONFIG  = c  11

# You can make your code fail to compile if it uses deprecated APIs.
# In order to do so, uncomment the following line.
#DEFINES  = QT_DISABLE_DEPRECATED_BEFORE=0x060000    # disables all the APIs deprecated before Qt 6.0.0

SOURCES  = \
    QMTIFF.cpp \
    main.cpp \
    mainwindow.cpp \
    processingBlock.cpp

HEADERS  = \
    QMTIFF.h \
    mainwindow.h \
    processingBlock.h

FORMS  = \
    mainwindow.ui

# Default rules for deployment.
qnx: target.path = /tmp/$${TARGET}/bin
else: unix:!android: target.path = /opt/$${TARGET}/bin
!isEmpty(target.path): INSTALLS  = target

DISTFILES  = \
    Morpho.py

LIBS  = -L"D:/workplace/Python/libs" -lpython310

INCLUDEPATH  = "D:/workplace/Python/include"
DEPENDPATH  = "D:/workplace/Python/include"

LIBS  = -L"D:/Qt/Qt5.15.2/5.15.2/Src/qtimageformats/src/3rdparty/libtiff/libtiff" -ltiff

INCLUDEPATH  = "D:/Qt/Qt5.15.2/5.15.2/Src/qtimageformats/src/3rdparty/libtiff/libtiff"
DEPENDPATH  = "D:/Qt/Qt5.15.2/5.15.2/Src/qtimageformats/src/3rdparty/libtiff/libtiff"