MinGW/Windows CRLF lunacy

[Matt]

I'm using g++ as packaged in MinGW running g++ from a command prompt 
under XP Home.

I'm filling a buffer with arbitrary binary data, then writing it to a 
file using fwrite.

I find that my file contains more bytes than I wrote, seemingly an extra 
byte for every '\n' that appeared in the buffer at an address divisible 
by 4.

Really I can hardly believe it, but there it is.  I have no such problem 
running the program under Linux.

What trick do I have to use to make the file contain exactly the data I 
send to fwrite?