So I've been doing some tests regarding enconding errors that I've seen around ñ charcater using CURL, Qt and sever side PHP. I've finally got a super minimalistic example where the error is in the Qt side ONLY. Maybe some one can help me out.
The Qt Code is as follows:
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
QString address = "http://localhost/api_test/test.php";
QUrl url(address);
QNetworkAccessManager manager;
QNetworkRequest request(url);
QNetworkReply *reply = manager.post(request, QByteArray());
QObject::connect(reply, &QNetworkReply::finished, QCoreApplication::quit);
a.exec();
if(reply->error() == QNetworkReply::NoError){
qDebug() << "The output";
qDebug() << QString(reply->readAll()).toUtf8();
}
else{
qDebug() << reply->error() << reply->errorString();
}
delete reply;
return 0;
}
On the server side, test.php is as follows:
<?php
$data = file_get_contents("uploaded.json");
echo "$data\n";
?>
Where "uploaded.json" is a plain text file that contains
{"name" : "Ariel ñoño", "age" : 58}
The curl command now works as expected
ariel#ColoLaptop:/home/web/api_test$ curl http://localhost/api_test/test.php
{"name" : "Ariel ñoño", "age" : 58}
But when I run the Qt Application, this happens:
The output
"{\"name\" : \"Ariel \xC3\xB1o\xC3\xB1o\", \"age\" : 58} \n\n"
Again the ñ characters get screwed. Can anyone tell me what is wrong with the Qt Code or how can I interpret the returned byte string correctly?
The "ñ" is unicode text so using toUtf8() won't do the trick. You have to use a QTextDecoder
qDebug() << "The output";
QTextCodec* codec = QTextCodec::codecForLocale();
QTextDecoder* decoder = codec->makeDecoder();
QString text = decoder->toUnicode(reply->readAll());
qDebug() << text;
Output:
The output
"{\"name\" : \"Ariel ñoño\", \"age\" : 58}\n"
I am currently having some trouble debugging a program that starts processes via QProcess.
Simply executing the binary without dbg works just fine but when I try to debug the executable with gdb I am getting a SIGTRAP when the process has started.
After that the stack always shows '??' instead of function names.
When continuing I get a SIGILL.
I found out that the trap is not caused when no breakpoint is set.
In my project I also get following output:
Probes-based dynamic linker interface failed.
I am not sure whether this is related to loaded plugins or libraries.
The problem can be reproduced (except from the " Probes-based dynamic linker interface failed." output) with the following code:
#include <QCoreApplication>
#include <QProcess>
#include <QDebug>
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
QProcess proc;
QString exe = "echo";
QStringList arguments;
arguments << "Test";
proc.start(exe, arguments);
if (!proc.waitForFinished()) {
qDebug() << "failed to start" << proc.exitCode() << proc.errorString();
}
qDebug() << "process finished";
qDebug() << proc.readAllStandardOutput();
return a.exec();
}
My OS is arch linux (up to date)
Qt5: qt5-base 5.15.1-1
GDB: gdb 9.2-1
clang++: clang 10.0.1-1
Does anybody have an idea what is causing the SIGTRAP when debugging with dbg?
I try to access a simple text file from a Qt-widget application with the QFile class for reading an writing. Reading the file line by line as a string works fine. But opening it ready to write fails. The following code checks if the file exists and tries to set the proper permissions, but in the end the file won't open.
Here is the failing piece of code:
#include "mainwindow.h"
#include <QApplication>
#include <QFile>
#include <QDebug>
int main(int argc, char *argv[]){
QApplication app(argc, argv);
MainWindow w;
w.show();
QFile file(":/test.dat");
qDebug() << "exists? " << file.exists();
qDebug() << "writable? " << file.isWritable();
qDebug() << "permissions before? " << file.permissions();
qDebug() << "permissions set? " << file.setPermissions(QFileDevice::WriteOther | QFileDevice::ReadOther);
qDebug() << "permissions after? " << file.permissions();
qDebug() << "opened? " << file.open(QIODevice::Append);
qDebug() << "errors? " << file.errorString();
qDebug() << "errnum? " << file.error();
QTextStream out(&file);
out << "something to append";
file.close();
return app.exec();
}
Qt returns this message:
exists? true
writable? false
permissions before? QFlags(0x4|0x40|0x400|0x4000)
permissions set? false
permissions after? QFlags(0x4|0x40|0x400|0x4000)
opened? false
errors? "Unknown error"
errnum? 5
QIODevice::write (QFile, ":/test.dat"): device not open
If I change the parameter in the open-function to QIODevice::ReadOnly the file is readable without problems, failing with QIODevice::WriteOnly. Why doesn't the same thing work for writing as well? Is it the permission? And why don't the permissions change after I called setPermissions? I run Qt as root on Ubuntu 14.04. And test.dat has full rights -rwxrwxrwx owned by user.
Can someone help?
Thanks!
The author is having Linux-related problem with writing to file created by console process with elevated privileges. I have fully reproduced the problem and when attempted to remove the file with:
vi \home\myuser\Documents\f.txt // create file like that from console
rm \home\myuser\Documents\f.txt // now try to remove it from console
I got "rm: remove write-protected regular file "\home\myuser\Documents\f.txt" and responded "yes" and then the code above shows after creating new file in the context of the program's process:
opened? true
exists? true
writable? true
permissions before? QFlags(0x4|0x20|0x40|0x200|0x400|0x2000|0x4000)
permissions set? true
permissions after? QFlags(0x4|0x20|0x40|0x200|0x400|0x2000|0x4000)
errors? "Unknown error"
errnum? 0
I run Qt Creator as root on Ubuntu 14.04.
It does not ensure the privileges of the program you run from it, I guess. UPDATE: make sure you run the program with appropriate permissions e.g. Root in this case.
According to qlogging.h
#define qDebug QMessageLogger(__FILE__, __LINE__, Q_FUNC_INFO).debug
but when I use like this, file,line,function name not show.
qDebug()<< "abc"; // only show abc;
qDebug()<< ""; // show nothing;
I search for a while, it seems no one had my problem like above.
I use ubuntu14.04,g++ version 4.8.2, qt5.3 build from git.
You can reformat from default output format.
This function was introduced in Qt 5.0.
The line number does not output because the default message pattern is "%{if-category}%{category}: %{endif}%{message}". This format means that the default outputting format is not including metadata like a line number or file name.
% cat logtest.pro
TEMPLATE = app
TARGET = logtest
mac:CONFIG-=app_bundle
SOURCES += main.cpp
% cat main.cpp
#include <QCoreApplication>
#include <QDebug>
int main(int argc, char *argv[])
{
qSetMessagePattern("%{file}(%{line}): %{message}");
QCoreApplication a(argc, argv);
qDebug() << "my output";
return 0;
}
% qmake && make
% ./logtest
main.cpp(8): my output
You can also use QT_MESSAGE_PATTERN environment variable for setting the message pattern without calling qSetMessagePattern().
See reference for other placeholder. http://qt-project.org/doc/qt-5/qtglobal.html#qSetMessagePattern
If you dig in Qt history you can find out that the __FILE__ and __FUNCTION__ are logged only in debug builds since 1 Oct 2014. The git commit hash is d78fb442d750b33afe2e41f31588ec94cf4023ad. The commit message states:
Logging: Disable tracking of debug source info for release builds
Tracking the file, line, function means the information has to be
stored in the binaries, enlarging the size. It also might be a
surprise to some commercial customers that their internal file &
function names are 'leaked'. Therefore we enable it for debug builds
only.
Here's a simple example of how you might use the captured QMessageLogContext data in a custom message handler installed using qInstallMessageHandler. I didn't output the category or version members because they didn't seem useful. If desired you could also log to a file this way.
#include <QDebug>
#include <QString>
#include <QDateTime>
#include <iostream>
void verboseMessageHandler(QtMsgType type, const QMessageLogContext &context, const QString &msg)
{
static const char* typeStr[] = {"[ Debug]", "[ Warning]", "[Critical]", "[ Fatal]" };
if(type <= QtFatalMsg)
{
QByteArray localMsg = msg.toLocal8Bit();
QString contextString(QStringLiteral("(%1, %2, %3)")
.arg(context.file)
.arg(context.function)
.arg(context.line));
QString timeStr(QDateTime::currentDateTime().toString("dd-MM-yy HH:mm:ss:zzz"));
std::cerr << timeStr.toLocal8Bit().constData() << " - "
<< typeStr[type] << " "
<< contextString.toLocal8Bit().constData() << " "
<< localMsg.constData() << std::endl;
if(type == QtFatalMsg)
{
abort();
}
}
}
int main()
{
//Use default handler
qDebug() << "default handler";
qWarning() << "default handler";
qCritical() << "default handler";
//Install verbose handler
qInstallMessageHandler(verboseMessageHandler);
qDebug() << "verbose handler";
qWarning() << "verbose handler";
qCritical() << "verbose handler";
//Restore default handler
qInstallMessageHandler(0);
qDebug() << "default handler";
qWarning() << "default handler";
qCritical() << "default handler";
return 0;
}
You can use standard C++'s __LINE__ and __FILE__. Also, take a look at What's the difference between __PRETTY_FUNCTION__, __FUNCTION__, __func__ SO question. If you use GCC, you can write __PRETTY_FUNCTION__ to get information about function from where the code executes. Just prepare debug-define you like.
For example, here is small compilable application:
#include <QApplication>
#include <QDebug>
#include <iostream>
// Qt-way
#define MyDBG (qDebug()<<__FILE__<<__LINE__<<__PRETTY_FUNCTION__)
// GCC
#define MyStdDBG (std::cout<< __FILE__<<":"<<__LINE__<<" in "<<__PRETTY_FUNCTION__<<std::endl)
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
// Qt-way
MyDBG;
MyDBG << "Something happened!";
// GCC
MyStdDBG;
return a.exec();
}
It gives next output:
../path/main.cpp 14 int main(int, char**)
../path/main.cpp 15 int main(int, char**) Something happened!
../path/main.cpp:18 in int main(int, char**)
UPD: Added pure C++-way to output.
I think you need to define:
#define qDebug() QMessageLogger(__FILE__, __LINE__, Q_FUNC_INFO).debug()
and use it as
qDebug() << "abc";
or
#define qDebug QMessageLogger(__FILE__, __LINE__, Q_FUNC_INFO).debug()
and use it as:
qDebug << "abc";
According to documentation qDebug() is already a macro to QMessageLogger(). Default Message handler prints only the message to stderr. I think you might want to use qInstallMessageHandler() to install your own message handler, that uses the context
Edit:
There is a relevant section in a manual, that describes this issue. In Qt4 context variable was not passed to installed message handler, so this solution is Qt5+ only. Default message handler does not make use of passed in context, but you can easily install your own, it's just a function pointer. There is even an example in the manual.
This depends on your Qt version number, whether you are using a debug build or a release build of Qt, and whether you have customized Qt message handling in your application.
According to Qt 5.4 documentation written in source code "qlogging.cpp":
QMessageLogger is used to generate messages for the Qt logging framework. Usually one uses
it through qDebug(), qWarning(), qCritical, or qFatal() functions,
which are actually macros: For example qDebug() expands to
QMessageLogger(__FILE__, __LINE__, Q_FUNC_INFO).debug()
for debug builds, and QMessageLogger(0, 0, 0).debug() for release builds.
So if you do not see file, line and function name information in your output, very likely you are using a release version of Qt.
If you still want to see the file, line and function name information in your output with a release version of Qt, there are several ways of achieving it, as very well explained in some of the previous answers.
If you wonder how to get the debug context in a non-debug build: Define QT_MESSAGELOGCONTEXT while compiling your code, and the information won't be stripped:
http://doc.qt.io/qt-5/qmessagelogcontext.html
I am trying to figure out the use of QProcess. I looked at Qt doc with no luck.
http://doc.qt.io/qt-4.8/qprocess.html
EXAMPLES OF PROBLEM.
Example 1: Code bellow works.
#include <QtCore/QCoreApplication>
#include <QTextStream>
#include <QByteArray>
#include <QProcess>
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
QTextStream qout(stdout);
QProcess cmd;
cmd.start("cmd");
if (!cmd.waitForStarted()) {
return false;
}
cmd.waitForReadyRead();
QByteArray result = cmd.readAll();
//qout << result.data() << endl; //console junk captured, doesn't show.
//My test command
cmd.write("echo hello");
cmd.write("\n");
//Capture my result
cmd.waitForReadyRead();
//This is my command shown by cmd, I don't show it, capture & discard it.
result = cmd.readLine();
//Read result of my command ("hello") and the rest of output like cur dir.
result = cmd.readAll();
qout << result.data();
qout << "\n\n---End, bye----" << endl;
return a.exec();
}
The output of the above code is
hello
F:\Dev_Qt\expControllingExtConsoleApps-build-desktop>
---End, bye----
The problem is that if I try to use ipconfig or 7zip in this fashion via Qprocess and cmd console, I am unable to see any output from ipconfig or 7zip. I don't know if anything is even done, if something is done then why can't I see the output? Code below illustrates.
Example 2: Does not work. Can't use ipconfig.
#include <QtCore/QCoreApplication>
#include <QTextStream>
#include <QByteArray>
#include <QString>
#include <QProcess>
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
QTextStream qout(stdout);
QProcess cmd2;
cmd2.setWorkingDirectory("C:/Program Files/7-Zip"); //not needed in this example.
cmd2.setReadChannel(QProcess::StandardOutput);
cmd2.setProcessChannelMode(QProcess::MergedChannels);
cmd2.start("cmd");
if (!cmd2.waitForStarted())
{
qout << "Error: Could not start!" << endl;
return false;
}
cmd2.waitForReadyRead();
QByteArray result = cmd2.readAll();
qout << result.data() << endl; //Console version info, etc.
//My command
cmd2.write("ipconfig");
cmd2.write("\n");
//Capture output of ipconfig command
//DOES NOT WORK!!
cmd2.waitForReadyRead();
while (! cmd2.atEnd())
{
result = cmd2.readLine();
qout << result;
result.clear();
}
qout << endl;
qout << "\n\n---end----" << endl;
return a.exec();
}
Output is below, it is missing the ipconfig connection information result. No output from ipconfig is captured at all.
Microsoft Windows XP [Version
5.1.2600] (C) Copyright 1985-2001 Microsoft Corp.
C:\Program Files\7-Zip> ipconfig
---end----
Should have been more like this (with ipconfig result).
Microsoft Windows XP [Version
5.1.2600] (C) Copyright 1985-2001 Microsoft Corp.
C:\Documents and
Settings\noname>ipconfig
Windows IP Configuration
Ethernet adapter Local Area
Connection:
Connection-specific DNS Suffix . :
IP Address. . . . . . . . . . . . : 192.172.148.135
Subnet Mask . . . . . . . . . . . : 255.255.255.0
Default Gateway . . . . . . . . . : 192.172.148.177
C:\Documents and Settings\noname>
Obviously the output should should have been a little diff than above but the Connection info which is the output of "ipconfig" should have been captured. In the same way if I try to use 7zip via cmd console... I can not see/capture any output of 7zip. So my question is how can I use command line apps like ipconfig and 7zip via QProcess and cmd console and see the result of the output of these applications?
Example 3: 7zip does not work
#include <QtCore/QCoreApplication>
#include <QTextStream>
#include <QByteArray>
#include <QProcess>
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
QTextStream qout(stdout);
QProcess cmd2;
cmd2.setWorkingDirectory("C:/Program Files/7-Zip");
cmd2.setReadChannel(QProcess::StandardOutput);
cmd2.setProcessChannelMode(QProcess::MergedChannels);
cmd2.start("cmd");
if (!cmd2.waitForStarted()) {
return false;
}
//My Command
cmd2.write("7z.exe");
cmd2.write("\n");
//Capture output of ipconfig command
cmd2.waitForReadyRead();
QByteArray result;
while (! cmd2.atEnd()) {
result = cmd2.readLine();
qout << result;
result.clear();
}
qout << endl;
qout << "\n\n---end----" << endl;
return a.exec();
}
Output below. Does not show anything from 7zip.
Microsoft Windows XP [Version
5.1.2600] (C) Copyright 1985-2001 Microsoft Corp.
C:\Program Files\7-Zip>7z.exe
---end----
Output is expected to be along the lines of...
Microsoft Windows XP [Version
5.1.2600] (C) Copyright 1985-2001 Microsoft Corp.
C:\Documents and Settings\noname>cd
C:\Program Files\7-Zip
C:\Program Files\7-Zip>7z.exe
7-Zip 9.15 beta Copyright (c)
1999-2010 Igor Pavlov 2010-06-20
Usage: 7z [...]
<archive_name> [<file_names>...]
[<#listfiles...>]
a: Add files to archive
b: Benchmark d: Delete files from
archive e: Extract files from
archive (without using directory
names) l: List contents of archive
t: Test integrity of archive u:
Update files to archive x: eXtract
files with full paths
-ai[r[-|0]]{#listfile|!wildcard}: Include archives
-ax[r[-|0]]{#listfile|!wildcard}: eXclude archives -bd: Disable
percentage indicator
-i[r[-|0]]{#listfile|!wildcard}: Include filenames -m{Parameters}:
set compression Method
-o{Directory}: set Output directory -p{Password}: set Password -r[-|0]: Recurse subdirectories -scs{UTF-8 |
WIN | DOS}: set charset for list files
-sfx[{name}]: Create SFX archive -si[{name}]: read data from stdin -slt: show technical information for l (List) command -so: write data to
stdout -ssc[-]: set sensitive case
mode -ssw: compress shared files
-t{Type}: Set type of archive -u[-][p#][q#][r#][x#][y#][z#][!newArchiveName]:
Update options -v{Size}[b|k|m|g]:
Create volumes -w[{path}]: assign
Work directory. Empty path means a
temporary directory
-x[r[-|0]]]{#listfile|!wildcard}: eXclude filenames -y: assume Yes on
all queries
C:\Program Files\7-Zip>
eI see one big problem.
Under windows you issue a commend pressing the Enter key. Writing
cmd.write("command");
cmd.write("\n");
just isn't enough you have to write
cmd.write("command");
cmd.write("\n\r");
Notice the trailing \r. Try this, it should work better, and by better I mean 7zip. I don't know if you'll get ipconfig to work properly.
Good luck and best regards
D
EDIT
Here is a working solution:
#include <QtCore/QCoreApplication>
#include <QtCore/QProcess>
#include <QtCore/QString>
#include <QtCore/QTextStream>
// Not clean, but fast
QProcess *g_process = NULL;
// Needed as a signal catcher
class ProcOut : public QObject
{
Q_OBJECT
public:
ProcOut (QObject *parent = NULL);
virtual ~ProcOut() {};
public slots:
void readyRead();
void finished();
};
ProcOut::ProcOut (QObject *parent /* = NULL */):
QObject(parent)
{}
void
ProcOut::readyRead()
{
if (!g_process)
return;
QTextStream out(stdout);
out << g_process->readAllStandardOutput() << endl;
}
void
ProcOut::finished()
{
QCoreApplication::exit (0);
}
int main (int argc, char **argv)
{
QCoreApplication *app = new QCoreApplication (argc, argv);
ProcOut *procOut = new ProcOut();
g_process = new QProcess();
QObject::connect (g_process, SIGNAL(readyReadStandardOutput()),
procOut, SLOT(readyRead()));
QObject::connect (g_process, SIGNAL(finished (int, QProcess::ExitStatus)),
procOut, SLOT(finished()));
g_process->start (QLatin1String ("cmd"));
g_process->waitForStarted();
g_process->write ("ipconfig\n\r");
// Or cmd won't quit
g_process->write ("exit\n\r");
int result = app->exec();
// Allright, process finished.
delete procOut;
procOut = NULL;
delete g_process;
g_process = NULL;
delete app;
app = NULL;
// Lets us see the results
system ("pause");
return result;
}
#include "main.moc"
Hope that helps. It worked everytime on my machine.
Even though Dariusz Scharsig already provided a solution to the problem, I would like to point out what I believe to be the actual problem(s) which can be solved using the signal slot mechanism.
Problem 1. The condition in your while loop is based on bool QProcess::atEnd () const which is according to QProcess Documentation states:
Reimplemented from QIODevice::atEnd().
Returns true if the process is
not running, and no more data is available for reading; otherwise
returns false.
But if you looking the documentation for QIODevice::atEnd(), it states:
Returns true if the current read and write position is at the end of
the device (i.e. there is no more data available for reading on the
device); otherwise returns false.
For some devices, atEnd() can return
true even though there is more data to read. This special case only
applies to devices that generate data in direct response to you
calling read() (e.g., /dev or /proc files on Unix and Mac OS X, or
console input / stdin on all platforms).
Solution 1. Change the while loop condition to check the state of your process: while(cmd2.state()!=QProcess::NotRunning){.
Problem 2. You use cmd2.waitForReadyRead(); outside of the loop. Perhaps some data is ready for reading now and when you finished reading, some more gets made available:
you read the commands you just wrote : ipconfig\n
ipconfig takes some time to start up and send text to the console. But by then you have already exited your loop because atEnd() gave true even though your process is still running.
Solution 2. place the waitForReadyRead() inside your loop.
Consequence 2. waitForReadyRead() will tell you when there is data available, which could be more than one Line, so you should consequently also change the cmd2.ReadLine() to cmd2.ReadAll().
Problem 3. As documented in QProcess::closeWriteChannel()
Closing the write channel is necessary for programs that read input
data until the channel has been closed.
Solution 3. One of the following options should work when finished writing your inputs
End the process: cmd2.write("exit\n");
close the Writechannel: cmd2.closeWriteChannel();
Working code:
#include <QtCore/QCoreApplication>
#include <QTextStream>
#include <QByteArray>
#include <QString>
#include <QProcess>
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
QTextStream qout(stdout);
QByteArray result;
QProcess cmd2;
cmd2.setReadChannel(QProcess::StandardOutput);
cmd2.setProcessChannelMode(QProcess::MergedChannels);
cmd2.start("cmd");
if (!cmd2.waitForStarted()){
qout << "Error: Could not start!" << endl;
return 0;
}
cmd2.write("ipconfig\n");
cmd2.closeWriteChannel(); //done Writing
while(cmd2.state()!=QProcess::NotRunning){
cmd2.waitForReadyRead();
result = cmd2.readAll();
qout << result;
}
qout << endl << "---end----" << endl;
return a.exec();
}
I wrote this answer just to explain the way I understand your problem and found a solution but would like to emphasize that the Preferable Solution is to use the Signal/Slot Mechanism as presented by Dariusz.