setbuf - assign buffering to a stream
Setbuf is used after a stream has been opened but before it is read or
written. It causes the character array buf to be used instead of an
automatically allocated buffer. If buf is the constant pointer NULL,
input/output will be completely unbuffered.
A manifest constant BUFSIZ tells how big an array is needed:
A buffer is normally obtained from malloc(3) upon the first getc or
putc(3) on the file, except that output streams directed to terminals,
and the standard error stream stderr are normally not buffered.
fopen(3), getc(3), putc(3), malloc(3)