I am trying to start a QProcess by
QProcess process= new QProcess();
process.start("javac file.java");
It starts successfully and I can see the output in the Qt Creator's log window. But when I try to read it from the program using process.readAll(), nothing was read. But when I try to do something like
process.start("echo Print this message");
then process.readAll() returns "Print this message".
Can anybody help me why this happens and how can I get that work. I am trying to make a simple IDE with it.
You're reading from the process's standard output channel, but your process outputs on the standard error channel. You need to read both. You also have the option of merging them. See QProcess documentation - read it and make sure you understand it. Edit your question to ask for clarification if anything is unclear.
Related
I can open a terminal by doing this from my QT code:
QProcess process;
process.start("xterm");
process.waitForFinished(-1);
But then I can't figure out how to write commands to it?
I need to do that because I want my app to ssh an equipment and then write commands once logged in and see the output.
I'm open to other solutions too!
Thanks
QProcess has a write command, but you don't want to be calling waitForFinished.
QProcess proc;
proc.start("xterm");
proc.waitForStarted();
proc.write(someData, dataSize);
If you want response from the terminal, connect a slot to the readyRead() signal
// Qt 5 syntax
connect(proc &QProcess::readyRead, this, &MyClass::readData());
Then call one of the read functions, such as readAll() from your readData slot function.
I need to write some commands in command window using C++ code. How to implement it. I have tried with CreateProcess function but it seems some wrong in it. Please refer my code below:
STARTUPINFO sInfo = {0};
sInfo.cb = sizeof(sInfo);
PROCESS_INFORMATION pInfo = {0};
CreateProcess("C:\\WINDOWS\\System32\\cmd.exe",""0,0,TRUE,
NORMAL_PRIORITY_CLASS,0,0,&sInfo,&pInfo);
It opens the command window successfully. My doubt is how to write command through code in it.
First thing, you need not to create a separate process just to write text output to a console window.
It depends what and how you want to write. You may create a console application itself, or create a console itself, and attach to the current process. You need to use pipes for the same and redirect the output to given pipe (i.e. send data to pipe). At the other end of pipe, you will read the text/buffer and render the output wherever you would like to.
These articles may help:
Console Output from GUI program
Real time Console Output redirection
Since your question is not very clear, this is just assumption.
Or, are you playing with the console itself - like changing colors, dimension etc?
I'm trying to execute a child_process synchronously in node.js (Yes, I know this is bad, I have a good reason) and retrieve any output on stdout, but I can't quite figure out how...
I found this SO post: node.js execute system command synchronously that describes how to use a library (node-ffi) to execute the command, and this works great, but the only thing I'm able to get is the process exit code. Any data the command executes is sent directly to stdout -- how do I capture this?
> run('whoami')
username
0
in otherwords, username is echo'd to stdout, the result of run is 0.
I'd much rather figure out how to read stdout
So I have a solution working, but don't exactly like it... Just posting here for reference:
I'm using the node-ffi library referenced in the other SO post. I have a function that:
takes in a given command
appends >> run-sync-output
executes it
reads run-sync-output synchronously and stores the result
deletes this tmp file
returns result
There's an obvious issue where if the user doesn't have write access to the current directory, it will fail. Plus, it's just wasted effort. :-/
I have built a node.js module that solves this exact problem. Check it out :)
exec-plan
Update
The above module solves your original problem, because it allows for the synchronous chaining of child processes. Each link in the chain gets the stdout from the previous process in the chain.
I had a similar problem and I ended up writing a node extension for this. You can check out the git repository. It's open source and free and all that good stuff !
https://github.com/aponxi/npm-execxi
ExecXI is a node extension written in C++ to execute shell commands
one by one, outputting the command's output to the console in
real-time. Optional chained, and unchained ways are present; meaning
that you can choose to stop the script after a command fails
(chained), or you can continue as if nothing has happened !
Usage instructions are in the ReadMe file. Feel free to make pull requests or submit issues!
However it doesn't return the stdout yet... Well, I just released it today. Maybe we can build on it.
Anyway, I thought it was worth to mention it. I also posted this to a similar question: node.js execute system command synchronously
Since Node version v0.11.12, there is a child_process.execSync function for this.
Other than writing code a little diferent, there's actually no reason to do anything synched.
What don't you like about this? (docs)
var exec = require('child_process').exec;
exec('whoami', function (error, username) {
console.log('stdout: %s', username);
continueWithYourCode();
});
In dbx i have a put a break on a particular function using stop.Like stop function. But it is not stopping there instead when i try to step in using step command I get this error
after line 17745: (noname) = #0xf1deaa3c
What could be the problem???
I don't recognize that output message. I can't guess what the message is likely to mean. Could you tell us what OS you are using? Is it Linux or Solaris or something else? What is the version of dbx?
I'm working on an application controller for a program that is spitting text directly to /dev/tty.
This is a production application controller that must be able to catch all text going to the terminal. Generally, this isn't a problem. We simply redirect stdout and stderr. This particular application is making direct calls to echo and redirecting the result to /dev/tty (echo "some text" > /dev/tty). Redirects via my application controller are failing to catch the text.
I do have the source for this application, but am not in a position to modify it, nor is it being maintained anymore. Any ideas on how to catch and/or throw away the output?
screen -D -m yourEvilProgram
should work. Much time passed sinced I used it, but if you need to read some of its output it could even be possible that you could utilize some sockets to read it.
[Added: two links, Rackaid and Pixelbeat, and the home page at GNU]
The classic solution to controlling an application like this is Expect, which sets up pseudo-terminals, does logging, and drives the controlled application from a script. It comes with lots of sample scripts so you can probably just adapt one to fit your needs.
This is what I did in python
import pty, os
pid, fd = pty.fork()
if pid == 0: # In the child process execute another command
os.execv('./my-progr', [''])
print "Execv never returns :-)"
else:
while True:
try:
print os.read(fd,65536),
except OSError:
break
I can't quite determine whether the screen program mentioned by #flolo will do what you need or not. It may, but I'm not sure whether there is a logging facility built in, which appears to be what you need.
There probably is a program out there already to do what you need. I'd nominate sudosh as a possibility.
If you end up needing to write your own, you'll probably need to use a pseudo-tty (pty) and have your application controller sit in between the user's real terminal connection and the the pty device, where it can log whatever you need it to log. That's not trivial. You can find information about this in Rochkind's "Advanced UNIX Programming, 2nd Edn" book, and no doubt other similar books (Stevens' "Advanced Programming in the UNIX Environment" book is a likely candidate, but I don't have a copy to verify that).