r ~ Open a file for read only. File pointer starts at the beginning of the file
w ~ Open a file for write only. Erases the contents of the file or creates a new file if it doesn't exist. File pointer starts at the beginning of the file
a ~ Open a file for write only. The existing data in file is preserved. File pointer starts at the end of the file. Creates a new file if the file doesn't exist
x ~ Creates a new file for write only. Returns FALSE and an error if file already exists
r+ ~ Open a file for read/write. File pointer starts at the beginning of the file
w+ ~ Open a file for read/write. Erases the contents of the file or creates a new file if it doesn't exist. File pointer starts at the beginning of the file
a+ ~ Open a file for read/write. The existing data in file is preserved. File pointer starts at the end of the file. Creates a new file if the file doesn't exist
x+ ~ Creates a new file for read/write. Returns FALSE and an error if file already exists