C File Programming - Replace a text in a file using POSIX Calls

Is there a way to replace any keyword in a text file using POSIX calls, without re creating the file.. If yes Please tell me how to do it..

Thanks in ad开发者_开发问答vance..

If the text and the replacement are the same size then you can open it with mode r+, seek, and then write. If their sizes are different then there is no way to replace without recreating.