Analysis on the issue that rn cannot be used to write a txt file into phpfwrite

The following describes the issue that rn cannot be used to wrap a line when fwrite in php writes a txt file, if you want to write a txt file with fwrite, you can refer to the following problem: rn cannot be used for line feed.
I haven't found a solution after trying for a long time!
I suddenly thought that I had read a book before and used this stuff to solve it!
I want to help my friends who need help in preventing future forgetting!
View the code directly:
The code is as follows:
$ Stream = fopen ("robots.txt", "w + ");
Fwrite ($ stream, "Have you got a new line? \ r \ n I already have a new line! ");
?>