hi iam doing signup function so,I need a function that should read all cookies from browser and it should cross-browser compatible
Undoable. The browser sends back to the server the cookies on each HTTP request. There is absolutely no other way, on the server side, to "read" cookies from a browser.
For the nitpickers: You can make the browser execute JavaScript which can read some cookies and send them back actively, but this will give you less cookies (the non HttpOnly ones) than a normal browser response.
Accessing cookies in a browser through security holes is clearly not cross-browser compatible.