I am trying to use the libfprint in my Qt application
#include <QtGui/QApplication>
#include "mainwindow.h"
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <libfprint/fprint.h>
int main(int argc, char *argv[])
{
int r = 1;
struct fp_dscv_dev *ddev;
struct fp_dscv_dev **discovered_devs;
struct fp_dev *dev;
struct fp_print_data *data;
r = fp_init();
QApplication a(argc, argv);
MainWindow w;
w.show();
return a.exec();
}
Compiling throws this error
/concept/main.cpp:31: undefined reference to `fp_init()'
I have been battling with this for a while now. Any idea what I can do to get past this point? Thanks in advance!
It's a problem with your linker - it cannot find necessary libraries. Did you pass necessary linker switches (something like -lfoo) instructing it to link with library you are trying to use?
Related
I have got FFmpeg compiled using MSYS2. I have a strange issue that appeared only recently.the app crashes.
This is my main file:
#include "mainwindow.h"
#include <QApplication>
#include <QDebug>
extern "C" {
#include <libavdevice/avdevice.h>
#include <libavformat/avformat.h>
#include <libavutil/avutil.h>
#include <libavcodec/avcodec.h>
}
int main(int argc, char *argv[])
{
//qDebug() << av_version_info();
// avdevice_register_all();
QApplication a(argc, argv);
MainWindow w;
w.show();
return a.exec();
}
The program runs but crashes if I call 'avdevice_register_all()' and others FFmpeg functions，but only call 'av_version_info()' is runs, not crashes.
I don't really know how to solve this?
I have already tried to use google solving the problem,but no result.
I know it is possible with QPrintPreviewWidget via currentPage() function, but is there a way to return current page in QPrintPreviewDialog? Since I like the default QPrintPreviewDialog's interface, and I don't feel confident enough to rebuild it myself, I would like to use QPrintPreviewDialog.
QPrintPreviewDialog is a QDialog that has a QPrintPreviewWidget as internal elements, so using findChild you can obtain that object.
#include <QApplication>
#include <QPrintPreviewDialog>
#include <QPrintPreviewWidget>
#include <QPrinter>
#include <QTimer>
#include <QTextCursor>
#include <QTextDocument>
#include <QDebug>
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
QPrintPreviewDialog previewDialog;
QObject::connect(&previewDialog, &QPrintPreviewDialog::paintRequested, &previewDialog, [&previewDialog](QPrinter *printer){
QTextDocument document;
QTextCursor cursor(&document);
QTextBlockFormat blockFormat;
for(int i=0; i < 10; i++){
cursor.insertBlock(blockFormat);
cursor.insertHtml(QString("<h1>This is the %1 page</h1>").arg(i+1));
blockFormat.setPageBreakPolicy(QTextFormat::PageBreak_AlwaysBefore);
}
document.print(printer);
if(QPrintPreviewWidget *previewWidget = previewDialog.findChild<QPrintPreviewWidget *>()){
qDebug() << previewWidget->currentPage();
// change page
QTimer::singleShot(100, previewWidget, [previewWidget](){
previewWidget->setCurrentPage(2);
});
}
});
previewDialog.exec();
}
I'm trying to set the LocalStorage location (sqlite db) for my QML application but once i rebuild and run the application i still can't see the subfolder, INI file and the sqlite DB created on the desired location (in a subfolder within the resources folder). Here is what's in my main file.
Appreciate any one could pint what's I'm doing wrong here?
#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQmlContext>
#include <QString>
#include <QDebug>
#include <QDir>
int main(int argc, char *argv[])
{
QGuiApplication app(argc, argv);
QQmlApplicationEngine engine;
engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
//engine.setOfflineStoragePath("qrc:/");
auto offlineStoragePath = QUrl::fromLocalFile(engine.offlineStoragePath());
engine.rootContext()->setContextProperty("offlineStoragePath", offlineStoragePath);
QString customPath = "qrc:/OffLineStorage";
QDir dir;
if(dir.mkpath(QString(customPath))){
qDebug() << "Default path >> "+engine.offlineStoragePath();
engine.setOfflineStoragePath(QString(customPath));
qDebug() << "New path >> "+engine.offlineStoragePath();
}
return app.exec();
}
By looking at the code snippet in your question, everything looks fine.
Anyway, you should verify if the following line actually returns true as you expect:
dir.mkpath(QString(customPath)
If no, the body of the if statement isn't executed in any case, thus setOfflineStoragePath is never invoked.
As a hint, using qrc:/OffLineStorage as a path for your storage doesn't seem to be a good idea. I'm not sure it will work once in the production environment (to be checked, it sounds strange, but it could work).
Try use engine.setOfflineStoragePath before engine.load.
Using qrc:/OffLineStorage as a path for your storage doesn't seem to
be a good idea. I'm not sure it will work once in the production
environment
#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQmlContext>
#include <QString>
#include <QDebug>
#include <QDir>
int main(int argc, char *argv[])
{
QGuiApplication app(argc, argv);
QQmlApplicationEngine engine;
QString customPath = "qrc:/OffLineStorage";
QDir dir;
if(dir.mkpath(QString(customPath))){
qDebug() << "Default path >> "+engine.offlineStoragePath();
engine.setOfflineStoragePath(QString(customPath));
qDebug() << "New path >> "+engine.offlineStoragePath();
}
engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
engine.clearComponentCache();
if (engine.rootObjects().isEmpty())
return -1;
return app.exec();
}
What is used to open urls with QDesktopServices::openUrl(...)?
xdg-open, kopen, selmademachanism or a mix of them? I ask because it fails on a scheme where xdg-open does not.
Edit: okay its getting even more curious: The missing scheme works in debug mode, but not in release mode...
Example code:
#include <QApplication>
#include <QDesktopServices>
#include <QUrl>
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
QDesktopServices::openUrl(QUrl("tg://resolve?domain=imagebot"));
}
The program name is GoToCell in the form I created a label and two push buttons and I wrote the code in main.cpp as follows:
#include <QtGui/QApplication>
#include<QDialog>
#include "ui_GoToCell.h"
#include "GoToCell.h"
int main(int argc, char *argv[]) {
QApplication a(argc, argv);
Ui::GoToCell ui;
QDialog *dialog=new QDialog;
ui.setupUi(dialog);
dialog->show();
return a.exec();
}
While running it I'm getting the following errors:
GoToCell is not a member of ui
What should I do?
I think you have misspelled object name in objectName property in the GoToCell.ui form.
Change it to GoToCell. It will then execute.