QProcess(3qt)QProcess(3qt)NAME
QProcess - Used to start external programs and to communicate with them
SYNOPSIS
#include <qprocess.h>
Inherits QObject.
Public Members
QProcess ( QObject * parent = 0, const char * name = 0 )
QProcess ( const QString & arg0, QObject * parent = 0, const char *
name = 0 )
QProcess ( const QStringList & args, QObject * parent = 0, const char *
name = 0 )
~QProcess ()
QStringList arguments () const
void clearArguments ()
virtual void setArguments ( const QStringList & args )
virtual void addArgument ( const QString & arg )
QDir workingDirectory () const
virtual void setWorkingDirectory ( const QDir & dir )
enum Communication { Stdin = 0x01, Stdout = 0x02, Stderr = 0x04,
DupStderr = 0x08 }
void setCommunication ( int commFlags )
int communication () const
virtual bool start ( QStringList * env = 0 )
virtual bool launch ( const QString & buf, QStringList * env = 0 )
virtual bool launch ( const QByteArray & buf, QStringList * env = 0 )
bool isRunning () const
bool normalExit () const
int exitStatus () const
virtual QByteArray readStdout ()
virtual QByteArray readStderr ()
bool canReadLineStdout () const
bool canReadLineStderr () const
virtual QString readLineStdout ()
virtual QString readLineStderr ()
PID processIdentifier ()
Public Slots
void tryTerminate () const
void kill () const
virtual void writeToStdin ( const QByteArray & buf )
virtual void writeToStdin ( const QString & buf )
virtual void closeStdin ()
Signals
void readyReadStdout ()
void readyReadStderr ()
void processExited ()
void wroteToStdin ()
void launchFinished ()
DESCRIPTION
The QProcess class is used to start external programs and to
communicate with them.
You can write to the started program's standard input, and can read the
program's standard output and standard error. You can pass command line
arguments to the program either in the constructor or with
setArguments() or addArgument(). The program's working directory can be
set with setWorkingDirectory(). If you need to set up environment
variables pass them to the start() or launch() functions (see below).
The processExited() signal is emitted if the program exits. The
program's exit status is available from exitStatus(), although you
could simply call normalExit() to see if the program terminated
normally.
There are two different ways to start a process. If you just want to
run a program, optionally passing data to its standard input at the
beginning, use one of the launch() functions. If you want full control
of the program's standard input (especially if you don't know all the
data you want to send to standard input at the beginning), use the
start() function.
If you use start() you can write to the program's standard input using
writeToStdin() and you can close the standard input with closeStdin().
The wroteToStdin() signal is emitted if the data sent to standard input
has been written. You can read from the program's standard output using
readStdout() or readLineStdout(). These functions return an empty
QByteArray if there is no data to read. The readyReadStdout() signal is
emitted when there is data available to be read from standard output.
Standard error has a set of functions that correspond to the standard
output functions, i.e. readStderr(), readLineStderr() and
readyReadStderr().
If you use one of the launch() functions the data you pass will be sent
to the program's standard input which will be closed once all the data
has been written. You should not use writeToStdin() or closeStdin() if
you use launch(). If you need to send data to the program's standard
input after it has started running use start() instead of launch().
Both start() and launch() can accept a string list of strings each of
which has the format, key=value, where the keys are the names of
environment variables.
You can test to see if a program is running with isRunning(). The
program's process identifier is available from processIdentifier(). If
you want to terminate a running program use tryTerminate(), but note
that the program may ignore this. If you really want to terminate the
program, without it having any chance to clean up, you can use kill().
As an example, suppose we want to start the uic command (a Qt command
line tool used with Qt Designer) and perform some operations on the
output (the uic outputs the code it generates to standard output by
default). Suppose further that we want to run the program on the file
"small_dialog.ui" with the command line options "-tr i18n". On the
command line we would write:
uic -tr i18n small_dialog.ui
A code snippet for this with the QProcess class might look like this:
UicManager::UicManager()
{
proc = new QProcess( this );
proc->addArgument( "uic" );
proc->addArgument( "-tr" );
proc->addArgument( "i18n" );
proc->addArgument( "small_dialog.ui" );
connect( proc, SIGNAL(readyReadStdout()),
this, SLOT(readFromStdout()) );
if ( !proc->start() ) {
// error handling
}
}
void UicManager::readFromStdout()
{
// Read and process the data.
// Bear in mind that the data might be output in chunks.
}
Although you may need quotes for a file named on the command line (e.g.
if it contains spaces) you shouldn't use extra quotes for arguments
passed to addArgument() or setArguments().
The readyReadStdout() signal is emitted when there is new data on
standard output. This happens asynchronously: you don't know if more
data will arrive later.
In the above example you could connect the processExited() signal to
the slot UicManager::readFromStdout() instead. If you do so, you will
be certain that all the data is available when the slot is called. On
the other hand, you must wait until the process has finished before
doing any processing.
Note that if you are expecting a lot of output from the process, you
may hit platform-dependent limits to the pipe buffer size. The solution
is to make sure you connect to the output, e.g. the readyReadStdout()
and readyReadStderr() signals and read the data as soon as it becomes
available.
Please note that QProcess does not emulate a shell. This means that
QProcess does not do any expansion of arguments: a '*' is passed as a
'*' to the program and is not replaced by all the files, a '$HOME' is
also passed literally and is not replaced by the environment variable
HOME and the special characters for IO redirection ('>', '|', etc.) are
also passed literally and do not have the special meaning as they have
in a shell.
Also note that QProcess does not emulate a terminal. This means that
certain programs which need direct terminal control, do not work as
expected with QProcess. Such programs include console email programs
(like pine and mutt) but also programs which require the user to enter
a password (like su and ssh).
Notes for Windows users
Some Windows commands, for example, dir, are not provided by separate
applications, but by the command interpreter. If you attempt to use
QProcess to execute these commands directly it won't work. One possible
solution is to execute the command interpreter itself (cmd.exe on some
Windows systems), and ask the interpreter to execute the desired
command.
Under Windows there are certain problems starting 16-bit applications
and capturing their output. Microsoft recommends using an intermediate
application to start 16-bit applications.
See also QSocket, Input/Output and Networking, and Miscellaneous
Classes.
Member Type Documentation
QProcess::Communication
This enum type defines the communication channels connected to the
process.
QProcess::Stdin - Data can be written to the process's standard input.
QProcess::Stdout - Data can be read from the process's standard output.
QProcess::Stderr - Data can be read from the process's standard error.
QProcess::DupStderr - Both the process's standard error output and its
standard output are written to its standard output. (Like Unix's
dup2().) This means that nothing is sent to the standard error output.
This is especially useful if your application requires that the output
on standard output and on standard error must be read in the same order
that they are produced. This is a flag, so to activate it you must pass
Stdout|Stderr|DupStderr, or Stdin|Stdout|Stderr|DupStderr if you want
to provide input, to the setCommunication() call.
See also setCommunication() and communication().
MEMBER FUNCTION DOCUMENTATIONQProcess::QProcess ( QObject * parent = 0, const char * name = 0 )
Constructs a QProcess object. The parent and name parameters are passed
to the QObject constructor.
See also setArguments(), addArgument(), and start().
QProcess::QProcess ( const QString & arg0, QObject * parent = 0, const char *
name = 0 )
Constructs a QProcess with arg0 as the command to be executed. The
parent and name parameters are passed to the QObject constructor.
The process is not started. You must call start() or launch() to start
the process.
See also setArguments(), addArgument(), and start().
QProcess::QProcess ( const QStringList & args, QObject * parent = 0, const
char * name = 0 )
Constructs a QProcess with args as the arguments of the process. The
first element in the list is the command to be executed. The other
elements in the list are the arguments to this command. The parent and
name parameters are passed to the QObject constructor.
The process is not started. You must call start() or launch() to start
the process.
See also setArguments(), addArgument(), and start().
QProcess::~QProcess ()
Destroys the instance.
If the process is running, it is not terminated! The standard input,
standard output and standard error of the process are closed.
You can connect the destroyed() signal to the kill() slot, if you want
the process to be terminated automatically when the instance is
destroyed.
See also tryTerminate() and kill().
void QProcess::addArgument ( const QString & arg ) [virtual]
Adds arg to the end of the list of arguments.
The first element in the list of arguments is the command to be
executed; the following elements are the command's arguments.
See also arguments() and setArguments().
Example: process/process.cpp.
QStringList QProcess::arguments () const
Returns the list of arguments that are set for the process. Arguments
can be specified with the constructor or with the functions
setArguments() and addArgument().
Note that if you want to iterate over the list, you should iterate over
a copy, e.g.
QStringList list = myProcess.arguments();
QStringList::Iterator it = list.begin();
while( it != list.end() ) {
myProcessing( *it );
++it;
}
See also setArguments() and addArgument().
bool QProcess::canReadLineStderr () const
Returns TRUE if it's possible to read an entire line of text from
standard error at this time; otherwise returns FALSE.
See also readLineStderr() and canReadLineStdout().
bool QProcess::canReadLineStdout () const
Returns TRUE if it's possible to read an entire line of text from
standard output at this time; otherwise returns FALSE.
See also readLineStdout() and canReadLineStderr().
void QProcess::clearArguments ()
Clears the list of arguments that are set for the process.
See also setArguments() and addArgument().
void QProcess::closeStdin () [virtual slot]
Closes the process's standard input.
This function also deletes any pending data that has not been written
to standard input.
See also wroteToStdin().
int QProcess::communication () const
Returns the communication required with the process, i.e. some
combination of the Communication flags.
See also setCommunication().
int QProcess::exitStatus () const
Returns the exit status of the process or 0 if the process is still
running. This function returns immediately and does not wait until the
process is finished.
If normalExit() is FALSE (e.g. if the program was killed or crashed),
this function returns 0, so you should check the return value of
normalExit() before relying on this value.
See also normalExit() and processExited().
bool QProcess::isRunning () const
Returns TRUE if the process is running; otherwise returns FALSE.
See also normalExit(), exitStatus(), and processExited().
void QProcess::kill () const [slot]
Terminates the process. This is not a safe way to end a process since
the process will not be able to do any cleanup. tryTerminate() is
safer, but processes can ignore a tryTerminate().
The nice way to end a process and to be sure that it is finished, is to
do something like this:
process->tryTerminate();
QTimer::singleShot( 5000, process, SLOT( kill() ) );
This tries to terminate the process the nice way. If the process is
still running after 5 seconds, it terminates the process the hard way.
The timeout should be chosen depending on the time the process needs to
do all its cleanup: use a higher value if the process is likely to do a
lot of computation or I/O on cleanup.
The slot returns immediately: it does not wait until the process has
finished. When the process terminates, the processExited() signal is
emitted.
See also tryTerminate() and processExited().
bool QProcess::launch ( const QByteArray & buf, QStringList * env = 0 )
[virtual]
Runs the process and writes the data buf to the process's standard
input. If all the data is written to standard input, standard input is
closed. The command is searched for in the path for executable
programs; you can also use an absolute path in the command itself.
If env is null, then the process is started with the same environment
as the starting process. If env is non-null, then the values in the
string list are interpreted as environment setttings of the form
key=value and the process is started with these environment settings.
For convenience, there is a small exception to this rule under Unix: if
env does not contain any settings for the environment variable
LD_LIBRARY_PATH, then this variable is inherited from the starting
process.
Returns TRUE if the process could be started; otherwise returns FALSE.
Note that you should not use the slots writeToStdin() and closeStdin()
on processes started with launch(), since the result is not well-
defined. If you need these slots, use start() instead.
The process may or may not read the buf data sent to its standard
input.
You can call this function even when a process that was started with
this instance is still running. Be aware that if you do this the
standard input of the process that was launched first will be closed,
with any pending data being deleted, and the process will be left to
run out of your control. Similarly, if the process could not be started
the standard input will be closed and the pending data deleted. (On
operating systems that have zombie processes, Qt will also wait() on
the old process.)
The object emits the signal launchFinished() when this function call is
finished. If the start was successful, this signal is emitted after all
the data has been written to standard input. If the start failed, then
this signal is emitted immediately.
See also start() and launchFinished().
bool QProcess::launch ( const QString & buf, QStringList * env = 0 ) [virtual]
This is an overloaded member function, provided for convenience. It
behaves essentially like the above function.
The data buf is written to standard input with writeToStdin() using the
QString::local8Bit() representation of the strings.
void QProcess::launchFinished () [signal]
This signal is emitted when the process was started with launch(). If
the start was successful, this signal is emitted after all the data has
been written to standard input. If the start failed, then this signal
is emitted immediately.
This signal is especially useful if you want to know when you can
safely delete the QProcess object when you are not interested in
reading from standard output or standard error.
See also launch() and QObject::deleteLater().
bool QProcess::normalExit () const
Returns TRUE if the process has exited normally; otherwise returns
FALSE. This implies that this function returns FALSE if the process is
still running.
See also isRunning(), exitStatus(), and processExited().
void QProcess::processExited () [signal]
This signal is emitted when the process has exited.
See also isRunning(), normalExit(), exitStatus(), start(), and
launch().
Example: process/process.cpp.
PID QProcess::processIdentifier ()
Returns platform dependent information about the process. This can be
used together with platform specific system calls.
Under Unix the return value is the PID of the process, or -1 if no
process belongs to this object.
Under Windows it is a pointer to the PROCESS_INFORMATION struct, or 0
if no process is belongs to this object.
Use of this function's return value is likely to be non-portable.
QString QProcess::readLineStderr () [virtual]
Reads a line of text from standard error, excluding any trailing
newline or carriage return characters and returns it. Returns
QString::null if canReadLineStderr() returns FALSE.
By default, the text is interpreted to be in Latin-1 encoding. If you
need other codecs, you can set a different codec with
QTextCodec::setCodecForCStrings().
See also canReadLineStderr(), readyReadStderr(), readStderr(), and
readLineStdout().
QString QProcess::readLineStdout () [virtual]
Reads a line of text from standard output, excluding any trailing
newline or carriage return characters, and returns it. Returns
QString::null if canReadLineStdout() returns FALSE.
By default, the text is interpreted to be in Latin-1 encoding. If you
need other codecs, you can set a different codec with
QTextCodec::setCodecForCStrings().
See also canReadLineStdout(), readyReadStdout(), readStdout(), and
readLineStderr().
QByteArray QProcess::readStderr () [virtual]
Reads the data that the process has written to standard error. When new
data is written to standard error, the class emits the signal
readyReadStderr().
If there is no data to read, this function returns a QByteArray of size
0: it does not wait until there is something to read.
See also readyReadStderr(), readLineStderr(), readStdout(), and
writeToStdin().
QByteArray QProcess::readStdout () [virtual]
Reads the data that the process has written to standard output. When
new data is written to standard output, the class emits the signal
readyReadStdout().
If there is no data to read, this function returns a QByteArray of size
0: it does not wait until there is something to read.
See also readyReadStdout(), readLineStdout(), readStderr(), and
writeToStdin().
Example: process/process.cpp.
void QProcess::readyReadStderr () [signal]
This signal is emitted when the process has written data to standard
error. You can read the data with readStderr().
Note that this signal is only emitted when there is new data and not
when there is old, but unread data. In the slot connected to this
signal, you should always read everything that is available at that
moment to make sure that you don't lose any data.
See also readStderr(), readLineStderr(), and readyReadStdout().
void QProcess::readyReadStdout () [signal]
This signal is emitted when the process has written data to standard
output. You can read the data with readStdout().
Note that this signal is only emitted when there is new data and not
when there is old, but unread data. In the slot connected to this
signal, you should always read everything that is available at that
moment to make sure that you don't lose any data.
See also readStdout(), readLineStdout(), and readyReadStderr().
Example: process/process.cpp.
void QProcess::setArguments ( const QStringList & args ) [virtual]
Sets args as the arguments for the process. The first element in the
list is the command to be executed. The other elements in the list are
the arguments to the command. Any previous arguments are deleted.
QProcess does not perform argument substitutions; for example, if you
specify "*" or "$DISPLAY", these values are passed to the process
literally. If you want to have the same behavior as the shell provides,
you must do the substitutions yourself; i.e. instead of specifying a
"*" you must specify the list of all the filenames in the current
directory, and instead of "$DISPLAY" you must specify the value of the
environment variable DISPLAY.
Note for Windows users. The standard Windows shells, e.g. command.com
and cmd.exe, do not perform file globbing, i.e. they do not convert a
"*" on the command line into a list of files in the current directory.
For this reason most Windows applications implement their own file
globbing, and as a result of this, specifying an argument of "*" for a
Windows application is likely to result in the application performing a
file glob and ending up with a list of filenames.
See also arguments() and addArgument().
void QProcess::setCommunication ( int commFlags )
Sets commFlags as the communication required with the process.
commFlags is a bitwise OR of the flags defined by the Communication
enum.
The default is Stdin|Stdout|Stderr.
See also communication().
void QProcess::setWorkingDirectory ( const QDir & dir ) [virtual]
Sets dir as the working directory for processes. This does not affect
running processes; only processes that are started afterwards are
affected.
Setting the working directory is especially useful for processes that
try to access files with relative paths.
See also workingDirectory() and start().
bool QProcess::start ( QStringList * env = 0 ) [virtual]
Tries to run a process for the command and arguments that were
specified with setArguments(), addArgument() or that were specified in
the constructor. The command is searched for in the path for executable
programs; you can also use an absolute path in the command itself.
If env is null, then the process is started with the same environment
as the starting process. If env is non-null, then the values in the
stringlist are interpreted as environment setttings of the form
key=value and the process is started in these environment settings. For
convenience, there is a small exception to this rule: under Unix, if
env does not contain any settings for the environment variable
LD_LIBRARY_PATH, then this variable is inherited from the starting
process; under Windows the same applies for the environment variable
PATH.
Returns TRUE if the process could be started; otherwise returns FALSE.
You can write data to the process's standard input with writeToStdin().
You can close standard input with closeStdin() and you can terminate
the process with tryTerminate(), or with kill().
You can call this function even if you've used this instance to create
a another process which is still running. In such cases, QProcess
closes the old process's standard input and deletes pending data, i.e.,
you lose all control over the old process, but the old process is not
terminated. This applies also if the process could not be started. (On
operating systems that have zombie processes, Qt will also wait() on
the old process.)
See also launch() and closeStdin().
Example: process/process.cpp.
void QProcess::tryTerminate () const [slot]
Asks the process to terminate. Processes can ignore this if they wish.
If you want to be certain that the process really terminates, you can
use kill() instead.
The slot returns immediately: it does not wait until the process has
finished. When the process terminates, the processExited() signal is
emitted.
See also kill() and processExited().
QDir QProcess::workingDirectory () const
Returns the working directory that was set with setWorkingDirectory(),
or the current directory if none has been explicitly set.
See also setWorkingDirectory() and QDir::current().
void QProcess::writeToStdin ( const QByteArray & buf ) [virtual slot]
Writes the data buf to the process's standard input. The process may or
may not read this data.
This function always returns immediately. The data you pass to
writeToStdin() is copied into an internal memory buffer in QProcess,
and when control goes back to the event loop, QProcess will starting
transferring data from this buffer to the running process. Sometimes
the data will be transferred in several payloads, depending on how much
data is read at a time by the process itself. When QProcess has
transferred all the data from its memory buffer to the running process,
it emits wroteToStdin().
Note that some operating systems use a buffer to transfer the data. As
a result, wroteToStdin() may be emitted before the running process has
actually read all the data.
See also wroteToStdin(), closeStdin(), readStdout(), and readStderr().
void QProcess::writeToStdin ( const QString & buf ) [virtual slot]
This is an overloaded member function, provided for convenience. It
behaves essentially like the above function.
The string buf is handled as text using the QString::local8Bit()
representation.
void QProcess::wroteToStdin () [signal]
This signal is emitted if the data sent to standard input (via
writeToStdin()) was actually written to the process. This does not
imply that the process really read the data, since this class only
detects when it was able to write the data to the operating system. But
it is now safe to close standard input without losing pending data.
See also writeToStdin() and closeStdin().
SEE ALSO
http://doc.trolltech.com/qprocess.html
http://www.trolltech.com/faq/tech.html
COPYRIGHT
Copyright 1992-2007 Trolltech ASA, http://www.trolltech.com. See the
license file included in the distribution for a complete license
statement.
AUTHOR
Generated automatically from the source code.
BUGS
If you find a bug in Qt, please report it as described in
http://doc.trolltech.com/bughowto.html. Good bug reports help us to
help you. Thank you.
The definitive Qt documentation is provided in HTML format; it is
located at $QTDIR/doc/html and can be read using Qt Assistant or with a
web browser. This man page is provided as a convenience for those users
who prefer man pages, although this format is not officially supported
by Trolltech.
If you find errors in this manual page, please report them to qt-
bugs@trolltech.com. Please include the name of the manual page
(qprocess.3qt) and the Qt version (3.3.8).
Trolltech AS 2 February 2007 QProcess(3qt)
