Compiling with external library failed "Cannot load library...

[Antonhermann79]

Hello,

i have to use the ftdi library D2xx.lib in my QT project.
For this I made a simple test project to learn how to use this lib.
I'm unsing QT 6.8.1 on windows 11 in the following configuration:

.PRO file:

QT       += core gui

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets

CONFIG += c++17

DEFINES += FTD2XX_STATIC

# 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 += \
    main.cpp \
    mainwindow.cpp

HEADERS += \
    3rdPatry/ftd2xx.h \
    mainwindow.h

FORMS += \
    mainwindow.ui

DISTFILES += \
        3rdParty/ftd2xx.lib

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

win32:CONFIG(release, debug|release): LIBS += -L$$PWD/./release/ -lftd2xx
else:win32:CONFIG(debug, debug|release): LIBS += -L$$PWD/./debug/ -lftd2xx
else:unix: LIBS += -L$$PWD/./ -lftd2xx

INCLUDEPATH += $$PWD/3rdParty
DEPENDPATH += $$PWD/3rdParty
LIBS += -L$$PWD/3rdParty -lftd2xx

win32-g++:CONFIG(release, debug|release): PRE_TARGETDEPS += $$PWD/3rdParty/libftd2xx.a
else:win32-g++:CONFIG(debug, debug|release): PRE_TARGETDEPS += $$PWD/3rdParty/libftd2xx.a
else:win32:!win32-g++:CONFIG(release, debug|release): PRE_TARGETDEPS += $$PWD/3rdParty/ftd2xx.lib
else:win32:!win32-g++:CONFIG(debug, debug|release): PRE_TARGETDEPS += $$PWD/3rdParty/ftd2xx.lib
else:unix: PRE_TARGETDEPS += $$PWD/3rdParty/libftd2xx.a

mainwindow.h:

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

QT_BEGIN_NAMESPACE
namespace Ui {
class MainWindow;
}
QT_END_NAMESPACE

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = nullptr);
    ~MainWindow();
    void slLoadLibrary();

private:
    Ui::MainWindow *ui;

    char OutputBuffer[16];			//Buffer to hold MPSSE commands
    char InputBuffer[16];			//Buffer to hold read bytes


};
#endif // MAINWINDOW_H

mainwindow.cpp:

#include "mainwindow.h"
#include "ui_mainwindow.h"

#include "ftd2xx.h"
#include<windows.h>

#include <QDebug>
#include <QLibrary>
#include <QMessageBox>

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    this->setWindowTitle(" uCtMOS SPI Interface Testprogramm");
    setParent(parent);

    QLibrary library("ftd2xx.lib");
    if(!library.load())
        qDebug() << library.errorString();
    if(library.load())
        qDebug() << "library loaded";

    statusBar()->showMessage(tr("uCtMOS SPI test bereit"));


}

MainWindow::~MainWindow()
{
    delete ui;
}

In the setup I selected the kit with the MSCV2022 64 Bit compiler.
I' shure using the static amd64 version of ftd2xx.lib.

My probelm is: When executing/debugging this simple application I got the message from the application/debugging output:
"Cannot load library ftd2xx.lib: %1 ist keine zulässige Win32-Anwendung."

Searching in Google gave me some information but unfortunately nothing which helps me to resolve my problem loading the library.

Because I'm not very familiar with windows applications I'm a littel lost about what's going wrong...

Thank you for your help.

[hskoglund]

Hi, on Windows QLibrary can only load .dlls, not .libs, that is probably why you get the error.
Look for a ftd2xx.dll...

[Antonhermann79]

Hi,

I deleted the static ftd2xx.lib in the 3rdParty - path and copied the ftd2xx64.dll and the corresponding ftd2xx.lib there...
... but got the same error message.
For the next test I renamed the fdt2xx64.dll to fdt2xx.dll but same result.

[hskoglund]

Did you also change to
QLibrary library("ftd2xx..dll");
in your code?

[SGaist]

Hi,

Out of curiosity, why are you using QLibrary to use ftd2xx ?

[aha_1980]

From my experience, it could be one of the following three (four) problems:

1. The runtime linker cannot find the library, because it is neither in the working directory of the executable nor in the PATH
2. The executable has another architecture (32 vs. 64 bit) than the library
3. The library has further dependencies that cannot be found (same as problem 1) or have different architecture (problem 2)
4. You are mixing debug and release libraries

Regards

[aha_1980]

... and if you are really lucky, you have a library with the wrong arch in the PATH that is found before the correct one.

[Antonhermann79]

Hi,

why I'm using QLibrary - the right question to resolve my problem!
I saw QLibrary in a code snipplet of a apperently similar case and tought this is the solution without thinking deeper...
But in deed I want a static linking so QLibrary isn't necessary to use.
Thanks for this advice (and of course the others, too) which leads me to the (simple) solution...

So basically I made the correct configuration in the .pro file.
But the consequences of the silly using a code snipplet confused me.
Deleting the code with QLibrary and the rest is working as expected.

So the probelm is solved!
Thank's a lot for your help.

Kind Regards

[SGaist]

Good !
Then please mark the thread as solved using the Topic Tool button or the three dotted menu beside the answer you deem correct so other forum members may know a solution has been found :-)