change or add letter in text file -C++ QT

Question

I`m working with text file, and I want to read a text file line by line, and if line start with # I want to write before it * for example I have this file:

hello
world
#house
tree

I want it to be:

hello
world
*#house
tree

and if it easier I dont mind to do: *house or instead all the line to do that:

hello
world
*
tree

Do you know how to do it? thank:)

Answer 1

thanks for your replies:) I understood that the best way is to Read the file line by line and write the modified version out into a new file. Then close and remove the old file and rename the new one. have a nice day:)