212 lines
7.9 KiB
C
212 lines
7.9 KiB
C
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/***
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*fread.c - read from a stream
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*
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* Copyright (c) 1989-2001, Microsoft Corporation. All rights reserved.
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*
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*Purpose:
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* Read from the specified stream into the user's buffer.
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*
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*Revision History:
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* 06-23-89 PHG Module created, based on asm version
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* 02-15-90 GJF _iob[], _iob2[] merge. Also, fixed copyright and
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* indents.
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* 03-19-90 GJF Made calling type _CALLTYPE1 and added #include
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* <cruntime.h>.
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* 08-14-90 SBM Compiles cleanly with -W3
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* 10-02-90 GJF New-style function declarators.
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* 01-22-91 GJF ANSI naming.
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* 03-27-92 DJM POSIX support.
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* 06-22-92 GJF Must return 0 if EITHER size-of-item or number-of-
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* item arguments is 0 (TNT Bug #523)
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* 08-26-92 GJF Include unistd.h for POSIX build.
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* 04-06-93 SKS Replace _CRTAPI* with __cdecl
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* 05-11-93 GJF Replaced BUFSIZ with _INTERNAL_BUFSIZ.
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* 10-22-93 GJF Fix divide-by-0 error in unbuffered case. Also,
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* replaced MTHREAD with _MT.
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* 12-30-94 GJF _MAC_ merge.
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* 03-07-95 GJF _[un]lock_str macros now take FILE * arg.
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* 03-02-98 GJF Exception-safe locking.
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* 01-04-99 GJF Changes for 64-bit size_t.
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* 05-17-99 PML Remove all Macintosh support.
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*
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*******************************************************************************/
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#include <cruntime.h>
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#ifdef _POSIX_
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#include <unistd.h>
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#endif
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#include <stdio.h>
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#include <mtdll.h>
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#include <io.h>
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#include <string.h>
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#include <file2.h>
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/***
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*size_t fread(void *buffer, size_t size, size_t count, FILE *stream) -
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* read from specified stream into the specified buffer.
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*
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*Purpose:
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* Read 'count' items of size 'size' from the specified stream into
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* the specified buffer. Return when 'count' items have been read in
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* or no more items can be read from the stream.
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*
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*Entry:
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* buffer - pointer to user's buffer
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* size - size of the item to read in
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* count - number of items to read
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* stream - stream to read from
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*
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*Exit:
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* Returns the number of (whole) items that were read into the buffer.
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* This may be less than 'count' if an error or eof occurred. In this
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* case, ferror() or feof() should be used to distinguish between the
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* two conditions.
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*
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*Notes:
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* fread will attempt to buffer the stream (side effect of the _filbuf
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* call) if necessary.
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*
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* No more than 0xFFFE bytes may be read in at a time by a call to
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* read(). Further, read() does not handle huge buffers. Therefore,
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* in large data models, the read request is broken down into chunks
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* that do not violate these considerations. Each of these chunks is
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* processed much like an fread() call in a small data model (by a
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* call to _nfread()).
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*
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* MTHREAD/DLL - Handled in three layers. fread() handles the locking
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* and DS saving/loading/restoring (if required) and calls _fread_lk()
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* to do the work. _fread_lk() is the same as the single-thread,
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* large data model version of fread(). It breaks up the read request
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* into digestible chunks and calls _nfread() to do the actual work.
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*
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* 386/MTHREAD/DLL - Handled in just the two layers since it is small
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* data model. The outer layer, fread(), takes care of the stream locking
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* and calls _fread_lk() to do the actual work. _fread_lk() is the same
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* as the single-thread version of fread().
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*
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*******************************************************************************/
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#ifdef _MT
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/* define locking/unlocking version */
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size_t __cdecl fread (
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void *buffer,
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size_t size,
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size_t count,
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FILE *stream
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)
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{
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size_t retval;
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_lock_str(stream); /* lock stream */
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__try {
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/* do the read */
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retval = _fread_lk(buffer, size, count, stream);
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}
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__finally {
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_unlock_str(stream); /* unlock stream */
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}
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return retval;
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}
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#endif
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/* define the normal version */
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#ifdef _MT
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size_t __cdecl _fread_lk (
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#else
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size_t __cdecl fread (
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#endif
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void *buffer,
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size_t size,
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size_t num,
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FILE *stream
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)
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{
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char *data; /* point to where should be read next */
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size_t total; /* total bytes to read */
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size_t count; /* num bytes left to read */
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unsigned bufsize; /* size of stream buffer */
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unsigned nbytes; /* how much to read now */
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unsigned nread; /* how much we did read */
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int c; /* a temp char */
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/* initialize local vars */
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data = buffer;
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if ( (count = total = size * num) == 0 )
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return 0;
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if (anybuf(stream))
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/* already has buffer, use its size */
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bufsize = stream->_bufsiz;
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else
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/* assume will get _INTERNAL_BUFSIZ buffer */
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bufsize = _INTERNAL_BUFSIZ;
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/* here is the main loop -- we go through here until we're done */
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while (count != 0) {
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/* if the buffer exists and has characters, copy them to user
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buffer */
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if (anybuf(stream) && stream->_cnt != 0) {
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/* how much do we want? */
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nbytes = (count < (size_t)stream->_cnt) ? (unsigned)count : stream->_cnt;
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memcpy(data, stream->_ptr, nbytes);
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/* update stream and amt of data read */
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count -= nbytes;
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stream->_cnt -= nbytes;
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stream->_ptr += nbytes;
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data += nbytes;
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}
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else if (count >= bufsize) {
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/* If we have more than bufsize chars to read, get data
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by calling read with an integral number of bufsiz
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blocks. Note that if the stream is text mode, read
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will return less chars than we ordered. */
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/* calc chars to read -- (count/bufsize) * bufsize */
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nbytes = ( bufsize ? (unsigned)(count - count % bufsize) :
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(unsigned)count );
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#ifdef _POSIX_
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nread = read(fileno(stream), data, nbytes);
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#else
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nread = _read(_fileno(stream), data, nbytes);
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#endif
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if (nread == 0) {
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/* end of file -- out of here */
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stream->_flag |= _IOEOF;
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return (total - count) / size;
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}
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else if (nread == (unsigned)-1) {
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/* error -- out of here */
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stream->_flag |= _IOERR;
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return (total - count) / size;
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}
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/* update count and data to reflect read */
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count -= nread;
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data += nread;
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}
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else {
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/* less than bufsize chars to read, so call _filbuf to
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fill buffer */
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if ((c = _filbuf(stream)) == EOF) {
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/* error or eof, stream flags set by _filbuf */
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return (total - count) / size;
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}
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/* _filbuf returned a char -- store it */
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*data++ = (char) c;
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--count;
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/* update buffer size */
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bufsize = stream->_bufsiz;
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}
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}
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/* we finished successfully, so just return num */
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return num;
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}
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