I have a text file containing these lines: 

```
a1     b00     2222 
a1     b01     233 
a1     b92     34444
a2     b00      2222
a2     b00      3333
a2     b01      3333

```

I want to read this file and filter the text using `QRegExp`

and fill the result into three `QComboBox combo1`, for the first matching case, `combo2` to the second matching case, and `combo3` to the third matching case.
The result looks like:

```
 combo1 
 a1 
 a2

```

when selecting a2 from the `combo1` then `combo2` will be

```
 combo2 
  b00   
  b01

```

and when selecting b00 from `combo2`, `combo3` will be

```
 combo3 
 2222 
 3333

```

I haven't worked with `QRegExp`, can someone show me how to accomplish this?