Starting batch file using QProcess.execute() on different Windows version - batch-file

Question

I'm new to QT and have been spending a lot of time on this issue now.
Starting a batch file like below on Windows 10 has no problem but fails at Windows 7 and Windows XP.
Qprocess process;
QString data = "test.bat";
int success = 0;
success=process.execute(data);
The above snippet works fine on Windows 10.
On Windows 7 and XP it works if the data is modified as below:
"cmd.exe /c start test.bat"
Why does this difference exist for different Windows version ?
Help much appreciated!!

Answer 1

The question cannot be really answered as the used code depends on the execution environment defined outside of the application by the parent process on starting the application and there is nothing posted how the application is started on Windows XP, Windows 7 and Windows 10.
test.bat is referenced with no path which means it must be found in the current directory set for the application coded in C++ using Qt5 by the parent process on execution of the Windows library function CreateProcess which is used also by Qt5 class QProcess on Windows.
A batch file is not an executable. It is a script file which needs a script interpreter which is for batch files since Windows NT4 the Windows command processor cmd.exe. So the Windows command processor must be executed to process the batch file which is most likely stored in the directory of the C++ coded application using Qt5.
It is highly recommended to write the C++ code with using Qt5 being independent on the current working directory of the application and the environment variables PATH and PATHEXT by using the following commented code.
#include <QCoreApplication>
#include <QDebug>
#include <QDir>
#include <QProcess>
int main(int argc, char **argv)
{
QCoreApplication qDemoApp(argc,argv);
// Get the fully qualified file name of the Windows command processor.
QString qsCmdFileName = qEnvironmentVariable("ComSpec");
// The environment variable ComSpec is usually defined on Windows
// as system environment variable, but check if really existing.
if(qsCmdFileName.isEmpty())
{
// Get the full path to the Windows directory not ending with the
// directory separator using the environment variable SystemRoot.
qsCmdFileName = qEnvironmentVariable("SystemRoot");
// It is very unlikely that this environment variable is not defined
// as it is always defined by the Windows shell, i.e. explorer.exe
// running as Windows shell. But it is nevertheless possible that
// the environment variable is not defined in the list of the
// environment variables of the current process. In this case use
// directory Windows on system drive as directory and hope this
// directory exists as otherwise the execution of cmd.exe fails.
if(qsCmdFileName.isEmpty())
{
qsCmdFileName = QDir::toNativeSeparators(QDir::rootPath()) + QStringLiteral("Windows");
}
qsCmdFileName.push_back(QStringLiteral("\\System32\\cmd.exe"));
}
// The process must be executed with the following command line on
// C:\Windows\System32\cmd.exe is the fully qualified file name of
// the Windows command processor and the application directory has
// the unusual path C:\Temp\Development & Test(!) containing the
// batch file Test.bat which is explicitly set as working directory.
// C:\Windows\System32\cmd.exe /D /E:ON /V:OFF /C Test.bat
QStringList lqsArgumentsList(QStringLiteral("/D"));
lqsArgumentsList.append(QStringLiteral("/E:ON"));
lqsArgumentsList.append(QStringLiteral("/V:OFF"));
lqsArgumentsList.append(QStringLiteral("/C"));
lqsArgumentsList.append(QStringLiteral("Test.bat"));
QProcess qWindowsCommandProcess;
qWindowsCommandProcess.setWorkingDirectory(QCoreApplication::applicationDirPath());
qWindowsCommandProcess.start(qsCmdFileName,lqsArgumentsList,QIODevice::NotOpen);
if(!qWindowsCommandProcess.waitForFinished(-1))
{
QChar qSpace(' ');
QString qsCommandLine = qsCmdFileName + qSpace;
qsCommandLine.push_back(lqsArgumentsList.join(qSpace));
qInfo().noquote().nospace() << "ERROR: Failed to execute\n" << qsCommandLine << "\nin the directory:\n\""
<< QDir::toNativeSeparators(QCoreApplication::applicationDirPath()) << QChar('\"');
return 1;
}
return 0;
}
The Windows command processor arguments /E:ON and /V:OFF can be removed if the batch file Test.bat contains at top
#echo off
setlocal EnableExtensions DisableDelayedExpansion
and has as last line
endlocal
to define the execution environment completely without depending on which environment is defined on starting cmd.exe respectively on Windows command processor defaults which Windows users could customize although usually not done by them as most batch files would not work anymore as expected by their authors on really doing that. Run in a command prompt window cmd /? for the usage help and read the Microsoft documentation about cmd for more details.
Good coded applications do not depend on execution environment properties defined outside of the application as much as possible. The code above depends on the environment variable ComSpec and if not defined on environment variable SystemRoot. The usage of these two environment variables could be also avoided, but that would require the usage of the native Windows library function GetSystemDirectory instead of Qt5 functions.
For testing this code create in application directory the batch file Test.bat with the single command line #echo Executed %0 at %TIME% in "%CD%">"%~n0.txt". Then create another batch file AppTest.bat with the following command lines with environment variable AppPath defined with correct path to the directory containing your executable and Test.bat and AppName defined correct with file name plus file extension of your application:
#echo off
setlocal EnableExtensions DisableDelayedExpansion
set "AppPath=C:\Full Path\To Application"
set "AppName=AppName.exe"
rem Set a directory different to application directory as current directory.
cd /D "%TEMP%"
call :TestRun "Use environment variable ComSpec defined with: %ComSpec%"
set "ComSpec=C:\Temp\cmd.exe"
call :TestRun "Use environment variable ComSpec defined with: %ComSpec%"
set "ComSpec="
call :TestRun "Use environment variable SystemRoot defined with: %SystemRoot%"
set "SystemRoot=C:\Temp"
call :TestRun "Use environment variable SystemRoot defined with: %SystemRoot%"
set "SystemRoot="
call :TestRun "Use environment variable SystemDrive defined with: %SystemDrive%"
set "SystemDrive=Z:"
call :TestRun "Use environment variable SystemDrive defined with: %SystemDrive%"
set "SystemDrive="
call :TestRun "Use environment variable SystemDrive not defined at all."
goto EndBatch
:TestRun
echo %~1
"%AppPath%\%AppName%"
if not errorlevel 1 if exist "%AppPath%\Test.txt" (
type "%AppPath%\Test.txt"
del "%AppPath%\Test.txt"
)
echo/
goto :EOF
:EndBatch
pause
endlocal
QDir::rootPath() makes use of the Windows system environment variable SystemDrive on being compiled without preprocessor macro Q_OS_WINRT defined.
The batch file AppTest.bat can be executed from within a command prompt window or with a double click on it in Windows File Explorer.