Why does open() create my file with the wrong permissions?

Question

I am trying to read some text from a file and write it to another using open(), read() and write().

This is my open()

Answer 1

Not strictly relevant to the question, but the accepted answer could use this clarifying point:

There is a relationship between rwx and its numerical representation that can be seen by treating the presence of a letter as a binary 1, and its absence as a binary 0.

e.g.

rwx  <-->  111 (binary) <-->  7 (octal)

r--  <-->  100 (binary) <-->  4 (octal)

-wx  <-->  011 (binary) <-->  3 (octal) 

As a further addendum, you may now consider the chmod command:

chmod 777 filename.extension --> rwxrwxrwx permissions

777 <--> 111 111 111 <--> rwx rwx rwx

or: chmod 654 filename.extension --> rw-r-x-r--

654 <--> 110 101 100 <--> rw- r-x r--

Hope this is informative!