QProcess：如何知道发送到shell的命令已经完成

Question

考虑以下代码（适用于Windows平台）：

 // Function called lots of times.
 void showText(QString str, QString filename, bool open = false)
 {
    static QProcess* myProcess = new QProcess();

    if (myProcess->state() == QProcess::NoRunning)
       myProcess->start("cmd.exe");

    <Code that creates "filename" and writes "str" in it>

    myProcess->write("Sanity cmds\r\n");

    <Wait to "Sanity cmds" to finish and check status
     before continuing>

    if (open) // True only sometimes.
        myProcess->write("start file.txt");
 }

在执行“start file.txt”之前，我怎么能等到“Sanity cmds”完成（最好是超时），并知道它的退出状态？如果前者失败，则不能执行后者。

我已经尝试过不同的方法，还有两个额外的考虑因素：

A) The "cmd.exe" process cannot be killed to open a new instance.
B) If "Sanity cmds" returns something to its standard output or error, such output cannot be discarded.