setvbuf

raw OCR

Assigns buffering to a stream.

Defined in header <stdio.h>

Syntax

#include <stdio.h>
int setvbuf(FILE   *stream, char  *huf, int type, size_t size);

Portability

DOS	UNIX	Windows	ANSI C	C++ only
■	■	■	■

Remarks

setvbuf causes the buffer hufio be used for I/O buffering instead of an automatically allocated buffer. It is used after the given stream is opened.

If huf is null, a buffer will be allocated using malloc; the buffer will use size as the amount allocated. The buffer will be automatically freed on close. The size parameter specifies the buffer size and must be greater than zero.

The parameter size is limited to a maximum	of 32,767. *

stdin and stdout are unbuffered if they are not redirected; otherwise, they are fully buffered. Unbuffered means that characters written to a stream are immediately output to the file or device, while buffered means that the characters are accumulated and written as a block.

The type parameter is one of the following:

_IOFBF The file is fully buffered. When a buffer is empty, the next input operation will attempt to fill the entire buffer. On output, the buffer will be completely filled before any data is written to the file.

_IOLBF The file is line buffered. When a buffer is empty, the next input operation will still attempt to fill the entire buffer. On output, however, the buffer will be flushed whenever a newline character is written to the file.

lONBF The file is unbuffered. The buf and size parameters are ignored. Each input operation will read directly from the file, and each output operation will immediately write the data to the file.

A common cause for error is to allocate the buffer as an automatic (local) variable and then fail to close the file before returning from the function where the buffer was declared.

Return value

setvbuf returns 0 on success. It returns nonzero if an invalid value is given for type or size, or if there is not enough space to allocate a buffer.

Example

#include <stdio.h>

int main(void)
{
   FILE *input, *output;
   char bufr[512];
   input = fopen("file.in",  "r+b");
   output = fopen("file.out" , "w");

   /* set up input stream  for minimal disk access, using our own character buffer
      V
   if (setvbuf (input, bufr, _IOFBF, 512) != 0)
      printf("failed to set up buffer  for input file\n");
   else
      printf("buffer set up  for input file\n");

   /* set up output stream  for line buffering using space that is obtained
      through an indirect call  to malloc */
   if (setvbuf (output, NULL, _IOLBF, 132) != 0)
      printf("failed to set up buffer  for output file\n");
   else
      printf("buffer set up  for output file\n");

   /* perform file I/O here  */

   /* close files */
   fclose(input);
   fclose(output);
return

Differences from modern implementations

Nothing recorded yet.

Modern references

These are search links, not yet checked by hand.

Stable link: /3.1/stdio.h/setvbuf/ · short form /3.1/setvbuf/