Can you open a file in read only mode?

All major operating systems allow developers to write code that can open a file in a variety of different ways, including "r" or "ro" (read-only) "rw" (read-write), "w" (write-only), and "a" (append, like "w" but starts at the end of the file, preserving the previous contents). In these operating systems, applications may choose to open a file as "read-only", which prevents accidental modification of the file by logic errors in the code.