this first routine works: I get content in the QString I can query:

@
void start_server()
{
QProcess *start_adb=new QProcess;
start_adb->start(adbfile + " start-server");
start_adb->waitForFinished(-1);
command=start_adb->readAll();
delete start_adb;

 if (command.contains("daemon started successfully"))
     serverRunning = true;
     else
     serverRunning = false;

}
@

The QString returns empty in the routine below:

@
if (!fileName.isEmpty() )
{

QMessageBox::StandardButton reply;
  reply = QMessageBox::question(this, "Install", "Install "+fileName+"?",
                                QMessageBox::Yes|QMessageBox::No);
  if (reply == QMessageBox::Yes)
  {
      QProcess *install_apk=new QProcess;
      install_apk->start(adbfile + " install -r" + fileName);
      install_apk->waitForFinished(-1);
      command=install_apk->readAll();
      delete install_apk;
      }

if (command.contains("failed"))
     install_failed  = true;
     else
     install_failed = false;

}

}

@

I can run this command manually and get output succeed or fail.