setvbuf.c

不错的东西 请查看 WINCE OS

//
// Copyright (c) Microsoft Corporation.  All rights reserved.
//
//
// This source code is licensed under Microsoft Shared Source License
// Version 1.0 for Windows CE.
// For a copy of the license visit http://go.microsoft.com/fwlink/?LinkId=3223.
//

/***
*setvbuf.c - set buffer size for a stream
*
*Purpose:
*   defines setvbuf() - set the buffering mode and size for a stream.
*
*******************************************************************************/

#include <cruntime.h>
#include <stdio.h>
#include <file2.h>
#include <malloc.h>
#include <internal.h>
#include <mtdll.h>
#include <limits.h>
#include <dbgint.h>

/***
*int setvbuf(stream, buffer, type, size) - set buffering for a file
*
*Purpose:
*   Controls buffering and buffer size for the specified stream.  The
*   array pointed to by buf is used as a buffer, unless NULL, in which
*   case we'll allocate a buffer automatically. type specifies the type
*   of buffering: _IONBF = no buffer, _IOFBF = buffered, _IOLBF = same
*   as _IOFBF.
*
*Entry:
*   FILE *stream - stream to control buffer on
*   char *buffer - pointer to buffer to use (NULL means auto allocate)
*   int type     - type of buffering (_IONBF, _IOFBF or _IOLBF)
*   size_t size  - size of buffer
*
*Exit:
*   return 0 if successful
*   returns non-zero if fails
*
*Exceptions:
*
*******************************************************************************/

int __cdecl setvbuf (
    FILE *str,
    char *buffer,
    int type,
    size_t size
    )
{
    REG1 _FILEX *stream;
    int retval=0;   /* assume good return */

    _ASSERTE(str != NULL);

    /*
     * (1) Make sure type is one of the three legal values.
     * (2) If we are buffering, make sure size is greater than 0.
     */
    if ( (type != _IONBF) && ((size < 2) || (size > INT_MAX) ||
         ((type != _IOFBF) && (type != _IOLBF))) )
        return(-1);

    /*
     * force size to be even by masking down to the nearest multiple
     * of 2
     */
    size &= (size_t)~1;

    /*
     * Init stream pointers
     */
    stream = str;

    /*
     * Lock the file
     */

    if (! _lock_validate_str(stream))
        return -1;

    /*
     * Flush the current buffer and free it, if it is ours.
     */
    _flush(stream);
    _freebuf(stream);

    /*
     * Clear a bunch of bits in stream->_flag (all bits related to
     * buffering and those which used to be in stream2->_flag2). Most
     * of these should never be set when setvbuf() is called, but it
     * doesn't cost anything to be safe.
     */
    stream->_flag &= ~(_IOMYBUF | _IOYOURBUF | _IONBF |
               _IOSETVBUF |
               _IOFEOF | _IOFLRTN | _IOCTRLZ);

    /*
     * CASE 1: No Buffering.
     */
    if (type & _IONBF) {
        stream->_flag |= _IONBF;
        buffer = (char *)&(stream->_charbuf);
        size = 2;
    }

    /*
     * NOTE: Cases 2 and 3 (below) cover type == _IOFBF or type == _IOLBF
     * Line buffering is treated as the same as full buffering, so the
     * _IOLBF bit in stream->_flag is never set. Finally, since _IOFBF is
     * defined to be 0, full buffering is simply assumed whenever _IONBF
     * is not set.
     */

    /*
     * CASE 2: Default Buffering -- Allocate a buffer for the user.
     */
    else if ( buffer == NULL ) {
        if ( (buffer = _malloc_crt(size)) == NULL ) {
            retval = -1;
            goto done;
        }
        stream->_flag |= _IOMYBUF | _IOSETVBUF;
    }

    /*
     * CASE 3: User Buffering -- Use the buffer supplied by the user.
     */
    else {
        stream->_flag |= _IOYOURBUF | _IOSETVBUF;
    }

    /*
     * Common return for all cases.
     */
    stream->_bufsiz = size;
    stream->_ptr = stream->_base = buffer;
    stream->_cnt = 0;
done:
    _unlock_str(stream);
    return(retval);
}