아래 도움말...
To specify that a given file is being opened or created in text mode append a t to the mode string (rt w+t and so on). Similarly to specify binary mode append a b to the mode string (wb a+b and so on). fopen also allows the t or b to be inserted between the letter and the + character in the mode string; for example rt+ is equivalent to r+t.

If a t or b is not given in the mode string the mode is governed by the global variable _fmode. If _fmode is set to O_B/INARY files are opened in binary mode. If _fmode is set to O_TEXT they are opened in text mode. These O_... constants are defined in fcntl.h.

fopen 님이 쓰신 글 :
: fp = fopen("scale_value.dat", "wb");
:
:  여기서 파일을 열고 읽기형식으로 열어라는 알겠습니다.
: 그런데 wb에서 b는 머조??