Two ways, Which one is better?

[ktk]

What do you mean "better"? They are perfectly equivalent. The second one is less code to type in. If that counts as "better" then it's better.

It also use one allocation less and has a slightly better chance to be exception save. I can't think of any situation where the first form is better.

[wysota]

This is really an academic talk. One allocation more or less doesn't make a difference, Qt doesn't use exceptions so only your code can be throwing one so you should know how/where to catch it, etc. These two are practically equivalent, the stack based is simpler to type in which is completely meaningless as well. There is a potential situation when a heap based dialogue would lead to a memory leak but then read my post about "enlightened users"