#include <stdio.h>

int setvbuf(FILE *restrict stream, char *restrict buf, int type, size_t size);


Partially implemented


IEEE Std 1003.1-2017


The 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:

  • _IOFB shall cause input/output to be fully buffered.

  • _IOLB shall cause input/output to be line buffered.

  • _IONB shall 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 setvbuf() and the argument size specifies the size of the array; otherwise, size may determine the size of a buffer allocated by the setvbuf() function. The contents of the array at any time are unspecified. For information about streams, see Standard I/O Streams.

Return value#

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.


The setvbuf() function may fail if:

  • EBADF - The file descriptor underlying stream is not valid.

The following sections are informative.



Known bugs#


See Also#

  1. Standard library functions

  2. Table of Contents