How to enter commands to diskpart using QProcess

i have problem with using QProcess class to format pendrive. I checked similar questions, but they didn't help me. How can I enter a few commands to diskpart.exe? It should be something like this?
QProcess process;
process.start("diskpart.exe",QStringList()<<"/C"<<"select disk 1"<<"clean");

QProcess process;
process.start("diskpart.exe",QStringList()<<"/C"<<"select disk 1"<<"clean");

Because it doesn't work, I tried also other solutions, but without result.
I would like to ask about running commands from txt file also, if I write them to txt file:

select disk 1
clean

select disk 1
clean

How to execute this? Because I failed with this too.
One more other question, how can I check a letter of pendrive in diskpart in c++? To select a specific pendrive which I select in comboBox in my program?

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