Format
#include <stdio.h>
int setvbuf(FILE *stream, char *buf, int type, size_t size);Language Level: ANSI
Threadsafe: Yes.
Description
The setvbuf() function allows control over the buffering strategy and buffer size for a specified stream. The setvbuf() function only works in ILE C when using the integrated file system. The stream must refer to a file that has been opened, but not read or written to.
The array pointed to by buf designates an area that you provide that the C library may choose to use as a buffer for the stream. A buf value of NULL indicates that no such area is supplied and that the C library is to assume responsibility for managing its own buffers for the stream. If you supply a buffer, it must exist until the stream is closed.
The type must be one of the following:
If type is _IOFBF or _IOLBF, size is the size of the supplied buffer. If buf is NULL, the C library takes size as the suggested size for its own buffer. If type is _IONBF, both buf and size are ignored.
The value for size must be greater than 0.
Return Value
The setvbuf() function returns 0 if successful. It returns nonzero if a value that is not valid was specified in the parameter list, or if the request cannot be performed.
The setvbuf() function has no effect on stdout, stdin, or stderr.
Warning: The array that is used as the buffer must still exist when the specified stream is closed. For example, if the buffer is declared within the scope of a function block, the stream must be closed before the function is ended and frees the storage allocated to the buffer.
Example that uses setvbuf()
This example sets up a buffer of buf for stream1 and specifies that input to stream2 is to be unbuffered.
#include <stdio.h>
#define BUF_SIZE 1024
char buf[BUF_SIZE];
FILE *stream1, *stream2;
int main(void)
{
stream1 = fopen("myfile1.dat", "r");
stream2 = fopen("myfile2.dat", "r");
/* stream1 uses a user-assigned buffer of BUF_SIZE bytes */
if (setvbuf(stream1, buf, _IOFBF, sizeof(buf)) != 0)
printf("Incorrect type or size of buffer\n");
/* stream2 is unbuffered */
if (setvbuf(stream2, NULL, _IONBF, 0) != 0)
printf("Incorrect type or size of buffer\n");
/* This is a program fragment and not a complete function example */
}Related Information