int setvbuf(FILE *restrict stream, char *restrict buf, int type,
IEEE Std 1003.1-2017
setvbuf() function may be used after the stream pointed to by stream is associated with an open file but
before any other operation (other than an unsuccessful call to
setvbuf()) is performed on the stream. The argument
type determines how stream shall be buffered, as follows:
_IOFBshall cause input/output to be fully buffered.
_IOLBshall cause input/output to be line buffered.
_IONBshall cause input/output to be unbuffered.
If buf is not a
null pointer, the array it points to may be used instead of a buffer allocated by
the argument size specifies the size of the array; otherwise, size may determine the size of a buffer allocated by
setvbuf() function. The contents of the array at any time are unspecified.
For information about streams, see Standard I/O Streams.
Upon successful completion,
setvbuf() shall return
0. Otherwise, it shall return a non-zero value if an invalid value is
given for type or if the request cannot be honored, and may set
errno to indicate the error.
setvbuf() function may fail if:
EBADF- The file descriptor underlying stream is not valid.
The following sections are informative.