fwrite.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.
//
/***
*fwrite.c - read from a stream
*
*
*Purpose:
*   Write to the specified stream from the user's buffer.
*
*******************************************************************************/

#include <cruntime.h>
#include <stdio.h>
#include <mtdll.h>
#include <string.h>
#include <file2.h>
#include <internal.h>

/***
*size_t fwrite(void *buffer, size_t size, size_t count, FILEX *stream) -
*   write to the specified stream from the specified buffer.
*
*Purpose:
*   Write 'count' items of size 'size' to the specified stream from
*   the specified buffer. Return when 'count' items have been written
*   or no more items can be written to the stream.
*
*Entry:
*   buffer  - pointer to user's buffer
*   size    - size of the item to write
*   count   - number of items to write
*   stream  - stream to write to
*
*Exit:
*   Returns the number of (whole) items that were written to the stream.
*   This may be less than 'count' if an error or eof occurred. In this
*   case, ferror() or feof() should be used to distinguish between the
*   two conditions.
*
*Notes:
*   fwrite will attempt to buffer the stream (side effect of the _flsbuf
*   call) if necessary.
*
*   No more than 0xFFFE bytes may be written out at a time by a call to
*   write(). Further, write() does not handle huge buffers. Therefore,
*   in large data models, the write request is broken down into chunks
*   that do not violate these considerations. Each of these chunks is
*   processed much like an fwrite() call in a small data model (by a
*   call to _nfwrite()).
*
*   This code depends on _iob[] being a near array.
*
*   MTHREAD/DLL - Handled in just two layers since it is small data
*   model. The outer layer, fwrite(), handles stream locking/unlocking
*   and calls _fwrite_lk() to do the work. _fwrite_lk() is the same as
*   the single-thread, small data model version of fwrite().
*
*******************************************************************************/


/* define locking/unlocking version */
size_t __cdecl fwrite (
    const void *buffer,
    size_t size,
    size_t count,
    FILEX *stream
    )
{
    size_t retval;

    if(!CheckStdioInit())
        return 0;

    if (! _lock_validate_str(stream))           /* lock stream */
        return 0;

    retval = _fwrite_lk(buffer, size, count, stream);  /* do the read */
    _unlock_str(stream);            /* unlock stream */
    return retval;
}

/* define the normal version */
size_t __cdecl _fwrite_lk (
    const void *buffer,
    size_t size,
    size_t num,
    FILEX *stream
    )
{
    const char *data;       /* point to where data comes from next */
    unsigned total;         /* total bytes to write */
    unsigned count;         /* num bytes left to write */
    unsigned bufsize;       /* size of stream buffer */
    unsigned nbytes;        /* number of bytes to write now */
    unsigned nwritten;      /* number of bytes written */
    int c;              /* a temp char */

    /* initialize local vars */
    data = buffer;
    count = total = size * num;
        if (0 == count)
            return 0;

    if (anybuf(stream))
        /* already has buffer, use its size */
        bufsize = stream->_bufsiz;
    else
        /* assume will get _INTERNAL_BUFSIZ buffer */
        bufsize = _INTERNAL_BUFSIZ;

    /* here is the main loop -- we go through here until we're done */
    while (count != 0) {
        /* if the buffer is big and has room, copy data to buffer */
        if (bigbuf(stream) && stream->_cnt != 0) {
            /* how much do we want? */
            nbytes = (count < (unsigned)stream->_cnt) ? count : stream->_cnt;
            memcpy(stream->_ptr, data, nbytes);

            /* update stream and amt of data written */
            count -= nbytes;
            stream->_cnt -= nbytes;
            stream->_ptr += nbytes;
            data += nbytes;
        }
        else if (count >= bufsize) {
            /* If we have more than bufsize chars to write, write
               data by calling write with an integral number of
               bufsiz blocks.  If we reach here and we have a big
               buffer, it must be full so _flush it. */

            if (bigbuf(stream)) {
                if (_flush(stream)) {
                    /* error, stream flags set -- we're out
                       of here */
                    return (total - count) / size;
                }
            }

            /* calc chars to read -- (count/bufsize) * bufsize */
            nbytes = ( bufsize ? (count - count % bufsize) :
                   count );

            nwritten = _write(stream, data, nbytes);
            if (nwritten == (unsigned)EOF) {
                /* error -- out of here */
                stream->_flag |= _IOERR;
                return (total - count) / size;
            }

            /* update count and data to reflect write */

            count -= nwritten;
            data += nwritten;

            if (nwritten < nbytes) {
                /* error -- out of here */
                stream->_flag |= _IOERR;
                return (total - count) / size;
            }
        }
        else {
            /* buffer full and not enough chars to do direct write,
               so do a _flsbuf. */
            c = *data;  /* _flsbuf write one char, this is it */
            if (_flsbuf(c, stream) == EOF) {
                /* error or eof, stream flags set by _flsbuf */
                return (total - count) / size;
            }

            /* _flsbuf wrote a char -- update count */
            ++data;
            --count;

            /* update buffer size */
            bufsize = stream->_bufsiz > 0 ? stream->_bufsiz : 1;
        }
    }

    /* we finished successfully, so just return num */
    return num;
}