fdopen.c

C语言库函数的原型,有用的拿去

/***
*fdopen.c - open a file descriptor as stream
*
*       Copyright (c) Microsoft Corporation. All rights reserved.
*
*Purpose:
*       defines _fdopen() - opens a file descriptor as a stream, thus allowing
*       buffering, etc.
*
*******************************************************************************/

#include <cruntime.h>
#include <msdos.h>
#include <stdio.h>
#include <file2.h>
#include <dbgint.h>
#include <internal.h>
#include <mtdll.h>
#include <tchar.h>
#include <errno.h>

/***
*FILE *_fdopen(filedes, mode) - open a file descriptor as a stream
*
*Purpose:
*       associates a stream with a file handle, thus allowing buffering, etc.
*       The mode must be specified and must be compatible with the mode
*       the file was opened with in the low level open.
*
*Entry:
*       int filedes - handle referring to open file
*       _TSCHAR *mode - file mode to use ("r", "w", "a", etc.)
*
*Exit:
*       returns stream pointer and sets FILE struct fields if successful
*       returns NULL if fails
*
*Exceptions:
*
*******************************************************************************/

FILE * __cdecl _tfdopen (
        int filedes,
        REG2 const _TSCHAR *mode
        )
{
        REG1 FILE *stream;
        int whileflag, tbflag, cnflag;
        int fileflag;

        _VALIDATE_RETURN(mode != NULL, EINVAL, NULL);


        _CHECK_FH_RETURN( filedes, EBADF, NULL );
        _VALIDATE_RETURN((filedes >= 0 && (unsigned)filedes < (unsigned)_nhandle), EBADF, NULL);
        _VALIDATE_RETURN((_osfile(filedes) & FOPEN), EBADF, NULL);


        /* Skip leading spaces */
        while (*mode == _T(' '))
        {
            ++mode;
        }

        /* First character must be 'r', 'w', or 'a'. */
        switch (*mode) {
            case _T('r'):
                fileflag = _IOREAD;
                break;
            case _T('w'):
            case _T('a'):
                fileflag = _IOWRT;
                break;
            default:
                _VALIDATE_RETURN(("Invalid file open mode",0), EINVAL, NULL);
        }

        /* There can be up to three more optional characters:
           (1) A single '+' character,
           (2) One of 'b' and 't' and
           (3) One of 'c' and 'n'.

           Note that currently, the 't' and 'b' flags are syntax checked
           but ignored.  'c' and 'n', however, are correctly supported.
        */

        whileflag=1;
        tbflag=cnflag=0;
        fileflag |= _commode;

        while(*++mode && whileflag)
            switch(*mode) {

                case _T(' '):
                    /* skip spaces */
                    break;

                case _T('+'):
                    if (fileflag & _IORW)
                        whileflag=0;
                    else {
                        fileflag |= _IORW;
                        fileflag &= ~(_IOREAD | _IOWRT);
                    }
                    break;

                case _T('b'):
                case _T('t'):
                    if (tbflag)
                        whileflag=0;
                    else
                        tbflag=1;
                    break;

                case _T('c'):
                    if (cnflag)
                        whileflag = 0;
                    else {
                        cnflag = 1;
                        fileflag |= _IOCOMMIT;
                    }
                    break;

                case _T('n'):
                    if (cnflag)
                        whileflag = 0;
                    else {
                        cnflag = 1;
                        fileflag &= ~_IOCOMMIT;
                    }
                    break;

                default:
                    _VALIDATE_RETURN(("Invalid file open mode",0), EINVAL, NULL);
            }

        /* Skip trailing spaces */
        while (*mode == _T(' '))
        {
            ++mode;
        }

        _VALIDATE_RETURN( (*mode == _T('\0')), EINVAL, NULL);

        /* Find a free stream; stream is returned 'locked'. */

        if ((stream = _getstream()) == NULL) {
            errno = EMFILE;
            return(NULL);
        }

        __try {
#ifndef CRTDLL
            _cflush++;  /* force library pre-termination procedure */
#endif  /* CRTDLL */

            stream->_flag = fileflag;
            stream->_file = filedes;
        }
        __finally {
            _unlock_str(stream);
        }

        return(stream);
}