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Shareing Files in C++

Posted on 1997-03-25
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Last Modified: 2012-06-27
how can i make file share in c++ fstream?
and not be the _FSOPEN or SOPEN.
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Question by:orenw
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Expert Comment

by:mrosen
ID: 1162456
In the third parameter to either the constructor or the open() function, you specify one of the following:

filebuf::openprot, which is equivalent to the operating system default, filebuf::sh_compat, under MS-DOS. The possible nProt values are as follows:
filebuf::sh_compat   Compatibility share mode (MS-DOS only).
filebuf::sh_none   Exclusive mode — no sharing.
filebuf::sh_read   Read sharing allowed.
filebuf::sh_write   Write sharing allowed.

let me know if this solves what you're asking
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Accepted Solution

by:
jmmougeolle earned 200 total points
ID: 1162457
This is the way the stream buf use sopen inside the CRT source:

***************************************************************************
****CALLING TO FILEBUFF::OPEN INSIDE FSTREAM::OPEN
***************************************************************************

void fstream::open(const char * name, int mode, int prot)
{
    if (is_open() || !(rdbuf()->open(name, mode, prot)))
        {
        istream::clear(istream::state | istream::failbit);
        ostream::clear(ostream::state | ostream::failbit);
        }
}

***************************************************************************
****USING SOPEN INSIDE FILEBUFF::OPEN
****where share is equalt to the prot param used upper
**** as an arg for  fstream::open
***************************************************************************

    share &= (sh_read|sh_write|sh_none); // ignore other bits
    if (share)  // optimization  openprot serves as default
        {
        switch (share)
            {
/*          case 03000 : Reserved for sh_compat  */

//          case sh_none :
            case 04000 :
                smode = _SH_DENYRW;
                break;
//          case sh_read :
            case 05000 :
                smode = _SH_DENYWR;
                break;
//          case sh_write :
            case 06000 :
                smode = _SH_DENYRD;
                break;
//          case (sh_read|sh_write) :
            case 07000 :
                smode = _SH_DENYNO;
                break;
            default :   // unrecognized value same as default
                break;
            };
        }

    x_fd = _sopen(name, dos_mode, smode, S_IREAD|S_IWRITE);

***************************************************************************

So using:
filebuf::sh_none is equal to SOPEN _SH_DENYRW;
filebuf::sh_read is equal to SOPEN  _SH_DENYWR;
filebuf::sh_write is equal to SOPEN _SH_DENYRW;
filebuf::sh_read|filebuf::sh_write is equal to SOPEN  _SH_DENYNO;

I think that's all the information you need to know!


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