fwrite.c

C标准库源代码

/***
*fwrite.c - read from a stream
*
*       Copyright (c) 1989-1997, Microsoft Corporation. All rights reserved.
*
*Purpose:
*       Write to the specified stream from the user's buffer.
*
*******************************************************************************/

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

/***
*size_t fwrite(void *buffer, size_t size, size_t count, FILE *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().
*
*******************************************************************************/


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

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

/* define the normal version */
#ifdef _MT
size_t __cdecl _fwrite_lk (
#else  /* _MT */
size_t __cdecl fwrite (
#endif  /* _MT */
        const void *buffer,
        size_t size,
        size_t num,
        FILE *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
#if defined (_M_M68K) || defined (_M_MPPC)
                /* assume will get BUFSIZ buffer */
                bufsize = BUFSIZ;
#else  /* defined (_M_M68K) || defined (_M_MPPC) */
                /* assume will get _INTERNAL_BUFSIZ buffer */
                bufsize = _INTERNAL_BUFSIZ;
#endif  /* defined (_M_M68K) || defined (_M_MPPC) */

        /* 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(_fileno(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;
}