I'm trying to create a simple "To Do list" app in QT Creator while coding the part that loads and saves the list from a file I get stuck on a problem.
If you enter a string like "Do my homework" the program threads the string as it should, but when you load the program again the save file got split in words. So it gets all the entries but each word separated ("Do", "my", "homework").
What is the solution? I tried working with 'char arrays' and 'getline' but they give me nothing but errors.
Here is my code for the save and load parts:
void MainWindow::LoadList(){
std::ifstream load_file("./data.bin");
char loader[255];
while (load_file >> loader){
QString Writer = QString::fromStdString(loader);
ui->lstTaskList->addItem(Writer);
}
}
void MainWindow::SaveList(){
std::ofstream save_file("./data.bin");
for (auto i = 0; i < ui->lstTaskList->count(); i++){
QString Saver = ui->lstTaskList->item(i)->text();
std::string saver = Saver.toStdString();
save_file << saver << std::endl;
}
}
Can anyone help me with this, please?
My thanks in advance...
The anwser was using QFile and QByteArray for me, I knew about QFile but it tries using basic "std" c++ till I learned more about QT.
Related
I'm using the pleora sdk to capture images from an external camera and I am able to successfully write the data to tiff image files on disk. My next step is to change the data storage to SQLite instead of disk files.
I have PvBuffer *lBuffer pointer working fine. Now I need to convert that data to a format I can use to write to SQLite. I'm using Qt on linux so the QByteArray would be very convenient.
This is kind of a specific question for the pleora sdk and Qt. I'm hoping someone has experience with this.
PvRawData *rawData = lBuffer->GetRawData();
QByteArray ba;
//Need to copy the data from rawData to ba.
Thank you in advance.
I found an answer and wanted to post in case anybody else has something similar. I uses the reintepret_cast method.
data = lBuffer->GetDataPointer()
imgSize = lBuffer->GetPayloadSize();
const char *d = reinterpret_cast<char *>(data);
QByteArray ba(d, imgSize);
QSqlQuery q = QSqlQuery( db );
q.prepare("INSERT INTO imgData (image) values (:imageData)");
q.bindValue(":imageData", ba);
if ( !q.exec() )
qDebug() << "Error inserting image into table: " << q.lastError() << endl;
else
qDebug() << "Query executed properly" << endl;
Using console, I want to write the desired user's input into a file via getline function inside the wFile function and then read it. I face with logical error during Runtime; whatever I as user write doesn't type into the output terminal and it doesn't succeed more steps. Apparently fwrite function with this feature in the libraries exists, but I want to write my own code differently this way. I think I must have neglected a point. Here's the code:
#include <QCoreApplication>
#include <QDebug>
#include <QFile>
#include <QString>
#include <QTextStream>
#include <String>
#include <cstdlib>
using namespace std;
void wFile(QString Filename)
{
QFile mFile(Filename);
QTextStream str(&mFile);
qDebug() << "what do you want to write in the desired file: ";
istream& getline (istream& is, string& str);
if (!mFile.open(QFile::WriteOnly | QFile::Text))
{
qDebug() << "could not open the file";
return;
}
mFile.flush();
mFile.close();
}
void read (QString Filename){
QFile nFile(Filename);
if(!nFile.open(QFile::ReadOnly | QFile::Text))
{
qDebug() << "could not open file for reading";
return;
}
QTextStream in(&nFile);
QString nText = in.readAll();
qDebug() << nText;
nFile.close();
}
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
QString nFilename ="P:/DocumentArminV.txt";
wFile(nFilename);
read(nFilename);
return a.exec();
}
Spoiler alarm: At the very end of this answer, there is a very simple recommendation for a fix.
What OP did
Concerning istream& getline (istream& is, string& str); in wFile(QString Filename):
This declares function getline() in function wFile().
This is a valid declaration concerning C++.
Concerning the sample code, I missed the respective headers. IMHO,
#include <istream> and
#include <string>
are required to make this compiling.
However, it is possible that the existing #includes include them indirectly. So, OP's code may even compile without them.
Declaring functions, which are not used as well as re-declaring functions which are already declared is somehow useless but not wrong.
To demonstrate this, I made a small sample:
#include <cstdio>
#include <istream>
#include <string>
void func()
{
puts("in func()\n");
std::istream& getline(std::istream&, std::string&);
// Even duplicated prototyping is accepted without complaints:
std::istream& getline(std::istream&, std::string&);
}
int main ()
{
func();
return 0;
}
compiles and runs perfectly.
Output:
in func()
Live Demo on coliru
What OP (probably) wanted
Using console, I want to write the desired user's input into a file via getline function inside the wFile function and then read it.
This sounds a bit confusing to me. std::getline(std::cin, ) can be used to read user input from console. May be, it's a bit bad wording only.
Assuming, the OP wanted to read input from console, obviously, declaring a function is not sufficient – it must be called to become effective:
#include <iostream>
void func()
{
std::cout << "Enter file name: ";
std::string fileName; std::getline(std::cin, fileName);
std::cout << "Got file name '" << fileName << "'\n");
}
int main ()
{
func();
return 0;
}
Output:
Enter file name: test.txt↵
Got file name 'test.txt'
Live Demo on coliru
C++ std vs. Qt
Qt is undoubtly built on top of the C++ std library. However, though it's possible it is not recommended to mix both APIs when it can be prevented (or there aren't specific reasons to do so).
Both, Qt and C++ std, are a possibility to write portable software.
Qt covers a lot of things which are provided in the std library as well but a lot of other things additionally which are not or not yet part of std. In some cases, the Qt is a bit less generic but more convenient though this is my personal opinion. IMHO, the following explains how I came to this:
std::string vs. QString
std::string stores a sequence of chars. The meaning of chars when exposed as glyph (e.g. printing on console or displaying in a window) depends on the encoding which is used in this exposing. There are lot of encodings which interprete the numbers in the chars in distinct ways.
Example:
std::string text = "\xc3\xbc";
Decoded/displayed with
Windows-1252: ü
UTF-8: ü
Based on character type of std::string, it is not possible to determine the encoding. Hence, an additional hint must be provided to decode this properly.
(AFAIK, it is similar for std::wstring and wchar_t.)
QString stores a sequence of Unicode characters. So, one universal encoding was chosen by design to mitigate the "encoding hell".
As long as the program operates on QString, no encoding issues should be expected. The same is true when combining QString with other functions of Qt. However, it becomes a bit more complicated when "leaving the Qt universe" – e.g. storing contents of a std::string to QString.
This is the point where the programmer has to provide the additional hint for the encoding of the contents in std::string. QString provides a lot of from...() and to...() methods which can be used to re-encode contents but the application programmer is still responsible to chose the right one.
Assuming that the intended contents of text should have been the ü (i.e. UTF-8 encoding), this can be converted to QString (and back) by:
// std::string (UTF-8) -> QString
std::string text = "\xc3\xbc";
QString qText = QString::fromUtf8(text.c_str());
// QString -> std::string (UTF-8)
std::string text2 = qText.toUtf8();
This has to be considered when input from std::cin shall be passed to QString:
std::cout << "Enter file name: ";
std::string input; std::getline(std::cin, input);
QString qFileName = QString::fromLocal8Bit(input);
And even now, the code contains a little flaw – the locale of std::cin might have changed with std::ios::imbue(). I must admit that I cannot say much more about this. (In daily work, I try to prevent this topic at all e.g. by not relying on Console input which I consider especially critical on Windows – the OS on which we usually deploy to customers.)
Instead, a last note about OP's code:
How to fix it
Remembering my above recommendation (not to mix std and Qt if not necessary), this can be done in Qt exclusively:
QTextStream qtin(stdin);
qtin.readline();
I must admit that I never did it by myself but found this in the Qt forum: Re: stdin reading.
I have an arm board with a touchscreen display, where I want to display the output from a certain function, vcm_test(). The output of this function is saved to a file called
test.txt . Now I am able to read the contents of the file test.txt and display it in my qtextEdit only if it is less than 50-60 lines. Whereas I have more than 7000 lines in the test.txt . When I try to display 7000 lines the arm board keeps reading and nothing is displayed until reading is complete. Is there any way to read and display after every line or say every 10 lines. I thought of using qProcess in readfile too, but I have no idea how I can do that.
connect(ui->readfil, SIGNAL(clicked()), SLOT(readfile()));
connect(ui->VCMon, SIGNAL(clicked()), SLOT(vcm_test()));
connect(ui->Offloaderon, SIGNAL(clicked()), SLOT(offloader_test()));
connect(ui->quitVCM, SIGNAL(clicked()),vcmprocess, SLOT(kill()));
connect(ui->quitoffloader, SIGNAL(clicked()),offloaderprocess, SLOT(kill()));}
MainWindow::~MainWindow(){
delete ui;}
void MainWindow::readfile(){
QString filename="/ftest/test.txt";
QFile file(filename);
if(!file.exists()){
qDebug() << "NO file exists "<<filename;}
else{
qDebug() << filename<<" found...";}
QString line;
ui->textEdit->clear();
if (file.open(QIODevice::ReadOnly | QIODevice::Text)){
QTextStream stream(&file);
while (!stream.atEnd()){
line = stream.readLine();
ui->textEdit->setText(ui->textEdit->toPlainText()+line+"\n");
qDebug() << "line: "<<line;}
}
file.close();}
void MainWindow::vcm_test(){
vcmprocess->start("/ftest/vcm_test_2");}
void MainWindow::offloader_test(){
offloaderprocess->start("/ftest/off_test_2");}
Any advice is really appreciated.Thanks.
You could use QApplication::processEvents() after reading every line and appending it to your text edit. But you should be really careful when using this, and I would not recommend doing so. You should also consider using QTextEdit::Append() instead of setText.
A better solution is to read the file in another thread and use signals and slots to send read data that you want to append to your QTextEdit.
The following code somehow fails to notice any files with non-ASCII characters in their names (Cyrillic characters, specifically):
for (int path = 1; path < argc; path++) {
QFileInfo fi(argv[path]);
if (fi.isDir()) {
QDir dir(argv[path], "", QDir::LocaleAware, QDir::AllEntries);
qDebug() << dir.entryList();
QDirIterator it(QString(argv[path]), QDirIterator::Subdirectories);
while (it.hasNext()) {
it.next();
qDebug() << it.fileInfo().absoluteFilePath();
/* Processing; irrelevant in the context of the question */
}
}
}
What exactly am I doing wrong here? How should I handle QDir and QDirIterator to make them aware of Cyrillic filenames?
The system locale is en_US.UTF-8.
Update: On Windows, everything works correctly.
Get cmd line parameters out of QApplication itself.
So
QApplication app(argc, argv);
QStringList args = app.arguments();
for(...)
Qt will handle encoding properly. But that will only fix problems with unicode on cmd line. Not sure if that is your main problem though.
EDIT:
fromLocal8Bit() probably doesn't work because it wasn't local encoding, but utf8. So fromUtf8() would work on linux and osx (but it won't work on windows). On *nuxes it depends on some environment variables (LS_LANG or something). I guess Qt takes everything into account and converts it properly. You can look at the constructor code for QApplication if you want to know exactly what they do.
Which part is failing? Reading the initial directory specified argv[path] or the iterator? If it's the former, you should convert byte strings to QString for file processing using QFile::decodeName. The default char* => QString conversion uses Latin-1, which is not what you want for file names.
Don't use argv[path] just like that when constructing the QStrings. This will treat the string as a latin1 string (which doesn't care about cyrillic characters). Try using
const QString dirName = QString::fromLocal8Bit( argv[path] );
at the top of your loop and then use dirName everywhere instead of argv[path].
There is a magic number associated with each binary file , does anyone know how to retrieve this information from the file?
file <file_name>
magic numbers are usually stored in (linux):
/usr/share/file/magic
also check this link, someone was trying to use libmagic to get the information in C program, might be useful if you're writing something yourself.
Use libmagic from the file package to try and sniff out the type of file if that's your goal.
There are no general "magic" numbers in binary files on unix, though different formats might define their own. The above library knows about many of those and also use various other heuristics to try and figure out the format/type of file.
The unix file command uses magic number. see the file man page for more.(and where to find the magic file )
Read this: http://linux.die.net/man/5/magic
It's complex, and depends on the specific file type you're looking for.
There is a file command which in turn uses a magic library, the magic library reads from a file found in /etc called magic (this is installation dependant and may vary), which details what are the first few bytes of the file and tells the file what kind of a file it is, be it, jpg, binary, text, shell script. There is an old version of libmagic found on sourceforge. Incidentally, there is a related answer to this here.
Hope this helps,
Best regards,
Tom.
Expounding on #nos's answer:
Example below uses the default magic database to query the file passed on the command line. (Essentially an implementation of the file command. See man libmagic for more details/functions.
#include <iostream>
#include <magic.h>
#include <cassert>
int main(int argc, char **argv) {
if (argc == 1) {
std::cerr << "Usage " << argv[0] << " [filename]" << std::endl;
return -1;
}
const char * fname = argv[1];
magic_t cookie = magic_open(0);
assert (cookie !=nullptr);
int rc = magic_load(cookie, nullptr);
assert(rc == 0);
auto f= magic_file(cookie, fname);
if (f ==nullptr) {
std::cerr << magic_error(cookie) << std::endl;
} else {
std::cout << fname << ' ' << f << std::endl;
}
}