php file operations

model describe

r	Open the file as read-only. The file pointer starts at the beginning of the file.
w	Open the file for writing only. Delete the contents of the file or create a new file if it does not exist. The file pointer starts at the beginning of the file.
a	Open the file for writing only. Existing data in the file will be preserved. The file pointer starts at the end of the file. Create a new file if the file does not exist.
x	Create new files as write only. Returns FALSE and an error if the file already exists.
r+	Open the file for reading/writing, and the file pointer starts at the beginning of the file.
w+	Open the file for reading/writing. Delete the file contents or create a new file if it does not exist. The file pointer starts at the beginning of the file.
a+	Open the file for reading/writing. Data already in the file will be retained. The file pointer starts at the end of the file. Create new file if it does not exist.
x+	Create new files for reading/writing. Returns FALSE and an error if the file already exists.

The above introduces the operation of PHP files, including aspects of content. I hope it will be helpful to friends who are interested in PHP tutorials.