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cheers,
Chris Maunder
The Code Project Co-founder
Microsoft C++ MVP
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cheers,
Chris Maunder
The Code Project Co-founder
Microsoft C++ MVP
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Please understand that I am asking here and it is NOT a Qt question.
My task is to start a new process - the parameters are "application" and its parameters.
The basic process builds a "Database" and I am not so sure about "bin/sh" - I guess it "runs" a shell...
It works and there is no need to get into why at this point.
The "problem" is - the "process" is running and I need to interact with it.
I can use "write" but I have no idea when and where and how.
In the enclosed snippet the "info\n" is "send" to the file ( shell?) before it is finished...
I do understand that Qt process can "wait for finished " and I can also get a SIGNAL when the file is actually done building. What I do not get - if the process is actually /physically building / writing a file - what does "wait for finished " waiting for ?
Again - I am not asking how to code Qt , I am asking how to code so I can "write" the additional stuff in right time.
std::string Database = BT_DATABASE_TEST;
std::string Command = "bluetoothctl ";
std::string command = Command + std::string(" | tee ") + Database + std::string(" | tee /tmp/temp");
QP->start("/bin/sh", QStringList() << "-c" << command.c_str());
qDebug()<< "TEST QProcess CONTINUE DEBUG point @line " << QString::number(__LINE__);
QP->waitForFinished();
QP->write("info\n"); writes too soon
qDebug() << QP->readAllStandardError();
qDebug() << QP->readAllStandardOutput();
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I am assuming that your QP pointer is a reference to an object of QProcess Class | Qt Core 6.3.2[^]. As stated in the documentation the start method assumes the device mode as ReadWrite, which if it follows the normal rules, suggests you can write to and read from the started process. But writing will only work if the started process is waiting for input on its stdin stream. As far as I can see your started process is a simple shell pipeline to write some data to stdout and a couple of files. So it is not likely to be waiting for input from an external source.
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After more research - I have two distinct usage of the "command" (QProcess) - one writes to the file and terminates and the other one is "interactive" - writes to the file and expects input.
As of now I can "monitor" the first one two ways - in code - wait for finished or using "finished" SIGNAL. Right now my SIGNAL is "readyWrite" which ( the name ) does not make much sense - BUT it works with non - interactive command. I am going to take a closer look at QProcess SIGNALs - at least make more sense with non interactive command.As of now I just start the QProcess , and I am not directly ( using SIGNALs) verifying it is actually running / started.
After I clean that up I'll take a look at interactive part. Not sure where to start.
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Member 14968771 wrote: Not sure where to start.
The logical place is a tutorial on QProcess. You can only communicate with an independent process in this way, when the input and output streams are connected. The default option to the start method sets QIODeviceBase::OpenMode mode = ReadWrite. Does that mean that you can write to the process or not? Only a QT expert can advise on the answer.
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I have verified that I can "write" to QProcess - the question remains when.
Until now the command I have been testing with - which is why I am reluctant to post in QT forum - has been one of the challenges. There is no definite pattern when the command is "single shot" or interactive - depends on how it has been used before.
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I am making progress - one of the issues was I was getting multiple "readyRead" SIGNAls.
Not sure why... Now I am getting only one per "start(...) " QProcess and my process stays open.
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1. Why putting #define in char "string" won't process the "command" to "start a new process" , however,
compiler is not giving an error ?
In debug mode I have literal BT_DATABASE_TEST in "command",
2. I need to make the primary text (*.txt) file a variable - how ?
#define BT_DATABASE_TEST "../../BT_DATABASE/BluetoothDatabase.txt"
const char *command = "bluetoothctl show | tee ../../BT_DATABASE/BluetoothDatabase.txt | tee /tmp/temp";
QP->start("/bin/sh", QStringList() << "-c" << command);
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1. You can concatenate strings. Like this:
#define BT_DATABASE_TEST "../../BT_DATABASE/BluetoothDatabase.txt"
const char *command = "bluetoothctl show | tee " BT_DATABASE_TEXT " | tee /tmp/temp";
2. Maybe something like this:
std::string var = "blah_blah.txt";
std::string command = std::string("bluetoothctl show | tee ") + var + std::string("" | tee /tmp/temp");
QP->start("/bin/sh", QStringList() << "-c" << command.c_str());
Mircea
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Basically I can build a string then "convert it" to char, Neat trick. Thanks
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Member 14968771 wrote: 1. Why putting #define in char "string"...
The preprocessor does not see #define directives inside string literals.
"One man's wage rise is another man's price increase." - Harold Wilson
"Fireproof doesn't mean the fire will never come. It means when the fire comes that you will be able to withstand it." - Michael Simmons
"You can easily judge the character of a man by how he treats those who can do nothing for him." - James D. Miles
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I can`t think of a way to store in an array objects of different type but with same base class so I`m going to use a STL container instead:
class somebaseclass
{
}
class derivedclass: private somebaseclass
{
}
class anotherderivedclass: private somebaseclass
{
}
vector<somebaseclass *> * AllObjects;
derivedclass * Derived1 = new derivedclass[1];
anotherderivedclass * Derived2 = new anotherderivedclass[1];
AllObjects->push_back((somebaseclass)Derived1);
AllObjects->push_back((somebaseclass)Derived2);
Is this how it should be done?
modified 4 days ago.
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That works but the more modern (and safe) way to do it is to use unique_ptr instead of raw pointers. Something like this:
std::unique_ptr<Base> p1 = make_unique<Derived1>(args1);
std::unique_ptr<Base> p2 = make_unique<Derived2>(args2);
std::vector<std::uniqe_ptr<Base>> container;
container.push_back (p1);
container.push_back (p2);
Mircea
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Yes. If objects belong to different classes, the only way to store them in a container is to use pointers, because the container allocates the same amount of memory for each entry. If you also want the container to delete an entry when you erase it, declare it as, for example, vector<unique_ptr<T>>.
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Quote: because the container allocates the same amount of memory for each entry
that is an interesting fact
modified 4 days ago.
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Yes, except for:
1. Why are you using an array size reference in your instantiations? All you should need is:
derivedclass * Derived1 = new derivedclass();
2. Your container is defined to use somebaseclass * types, so your calls to push_back should be:
AllObject->push_back((somebaseclass*)Derived1);
or better still, using proper C++ casts:
AllObject->push_back(reinterpret_cast<somebaseclass*>(Derived1));
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You are welcome. I also think @Mircea-Neacsu's advice about unique_ptr is well worth taking.
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pointers from a library, that`s a topic that`s a bit too advanced or complicated for my present day understanding.
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If you can handle raw pointers, then C++ smart pointers should be easy to understand. Google for C++ unique_pointer tutorial and read through a few of the returned hits. It's fairly straight forward, and in general new C++ development should use the smart pointers instead of using raw (e.g. new/delete).
Keep Calm and Carry On
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The problem is I hate complicated syntax. Containers are already complicated syntax for me, combine that with another object (pointer) from a library and it becomes unintelligible mess. I will use a complicated feature when I really need to use it and there is no other way around it. Usually I need to use a feature a couple months before I can move on to something more complicated.
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It's a lot simpler than classes and inheritance. 
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Richard you really think so?
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