In one road bike i have the handlebar is 42cm. that i feel is good for me. In my other two bike the handlebars is 39cm and 45cm that is much difference from the 42cm?

It sounds like one is 3cm narrower and another is 3cm wider.

Do you have any discomfort with the narrower or wider bars?

Well, yeah, the 39 is 3 cm smaller and the 45 is 3 cm larger. Which one do you like best?

Seems like if you have to ask, then to you it doesn't make much difference. To others it might.

It sounds to me that English isn't your first language. Like the others, I don't really know what your asking.

For racing. handlebars are usually set at the width of your shoulders which is a good compromise. Wider bars can be more comfortable and often used for touring but they are less aerodynamic. Narrow bars are possibly more aerodynamic but make it harder to breath.

Anthony