c/io/setvbuf

Changes the buffering mode of the given file stream as indicated by the argument. In addition,


 * If is a null pointer, resizes the internal buffer to.
 * If is not a null pointer, instructs the stream to use the user-provided buffer of size  beginning at . The stream must be closed (with fclose) before the lifetime of the array pointed to by  ends. The contents of the array after a successful call to  are indeterminate and any attempt to use it is undefined behavior.

Return value
on success or nonzero on failure.