setvbuf (Windows CE 5.0)

项目
09/14/2012

Developing an Application > Microsoft C Run-time Library for Windows CE > Run-time Library Reference

This function controls stream buffering and buffer size.

int setvbuf(
  FILE*stream,char*buffer,intmode,size_tsize);

Parameters

stream
Pointer to FILE structure.
buffer
User-allocated buffer.
mode
Mode of buffering.
size
Buffer size in bytes. Allowable range: 2 <= size <= INT_MAX (2147483647). Internally, the value supplied for size is rounded down to the nearest multiple of 2.

Return Values

Returns 0 if successful, or a nonzero value if an illegal type or buffer size is specified.

Remarks

These functions are supported by all versions of the C run-time libraries.

The setvbuf function allows the program to control both buffering and buffer size for stream. stream must refer to an open file that has not undergone an I/O operation since it was opened.

The array pointed to by buffer is used as the buffer, unless it is NULL, in which case setvbuf uses an allocated buffer of length size/2 * 2 bytes.

The mode must be _IOFBF, _IOLBF, or _IONBF. If mode is _IOFBF or _IOLBF, then size is used as the size of the buffer. If mode is _IONBF, the stream is unbuffered and size and buffer are ignored.

Values for mode and their meanings are as follows:

Value	Description
_IOFBF	Full buffering; that is, buffer is used as the buffer and size is used as the size of the buffer. If buffer is NULL, an automatically allocated buffer size bytes long is used.
_IOLBF	For some systems, this provides line buffering. However, for Win32, the behavior is the same as _IOFBF - Full Buffering.
_IONBF	No buffer is used, regardless of buffer or size.

Example

Description

This program opens two streams: stream1 and stream2. It then uses setvbuf to give stream1 a user-defined buffer of 1024 bytes and stream2 no buffer.

Code

#include <stdio.h>

int main( void )
{
   char buf[1024];
   FILE *stream1, *stream2;

   if( ((stream1 = fopen( "data1", "a" )) != NULL) &&
       ((stream2 = fopen( "data2", "w" )) != NULL) )
   {
      if( setvbuf( stream1, buf, _IOFBF, sizeof( buf ) ) != 0 )
         printf( "Incorrect type or size of buffer for stream1\n" );
      else
         printf( "'stream1' now has a buffer of 1024 bytes\n" );
      if( setvbuf( stream2, NULL, _IONBF, 0 ) != 0 )
         printf( "Incorrect type or size of buffer for stream2\n" );
      else
         printf( "'stream2' now has no buffer\n" );
      _fcloseall();
   }
}
// Output
'stream1' now has a buffer of 1024 bytes
'stream2' now has no buffer

Requirements

OS Versions: Windows CE 2.0 and later.

Required header: stdio.h.

Link Library: coredll.dll.

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