Problem with CreateFileMapping() function

Dear Experts,

i have a problem with CreateFileMapping() function ,
i am trying in this way,

Code:

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hnd = (Mbyte*)CreateFile(fname, GENERIC_WRITE, NULL, NULL, OPEN_ALWAYS, FILE_ATTRIBUTE_NORMAL,NULL);

printf("\n in if _hMap==============%d",(int)_hnd);//which gives me some 2060
_hMap = (char *)CreateFileMapping(_hnd,NULL,MAPPROTWRMODE,_fileSize,NULL);

printf("\n in if mapHandle==============%d",(int)_hmap);//which gives me NULL

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why my map is getting failed when i can succesfully create a file,
i want the map for the file the "fname" specified in createfile please help me what can be the reason please provide me some solution.

Did you just type that out of your head?

1. Remove all the casts, and declare the variables properly.
2. http://msdn.microsoft.com/en-us/libr...37(VS.85).aspx - 6 params, you have 5.

BTW, since this question is clearly Windows specific (because you're talking about Windows API functions), you should be posting it in the Windows Programming forum instead of the general C++ forum. Just to keep things more organized and get the right kind of help.

Oh yes, now that you mention it... moved.

dear Experts,
sorry that i might have posted in the wrong forum,
but please tell me the solution to my problem,
if i remove the casts also the createFileMapping() is getting failed,
please tell me what is wrong because i used many examples to test ,
but there was not output please tell me what to do,

Code:

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hnd = CreateFile(fname, GENERIC_WRITE, NULL, NULL, OPEN_ALWAYS, FILE_ATTRIBUTE_NORMAL,NULL);

_hMap =CreateFileMapping(_hnd,NULL,MAPPROTWRMODE,_fileSize,NULL);

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this _hmap is failing,what is wrong plz help me.

You couldn't have found any examples like that, since as Salem points out it takes six arguments not five. (The last being "optional" only means you can pass in 0/NULL, not that you can pass in nothing at all.) Also, MAPPROTWRMODE is not listed as a valid value for the third value. (Actually, it looks like you're trying to make "_fileSize" play the part of the fourth and fifth arguments together.)

Dear experts,

sorry for sending that code actually it was

Code:

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#define MAPPROTWRMODE        PAGE_READWRITE

hnd = CreateFile(fname, GENERIC_WRITE, NULL, NULL, OPEN_ALWAYS, FILE_ATTRIBUTE_NORMAL,NULL);

_hMap =CreateFileMapping(_hnd,NULL,MAPPROTWRMODE,0,_fileSize,NULL);

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this is the actual one which is syntactically correct but returning NULL,
so know any corrections you suggest.

You should check GetLastError.

But I would guess that since you opened the file with write privileges, trying to map it with read/write privileges may not work.

Dear experts,
thanks for reply,
but that is not the solution as iam opening the file in GENERIC_WRITE,so it will write instead of read,
any more solutions.

I doubt that's what GetLastError said.

(Edit: by that I mean "but that is not the solution as iam opening the file in GENERIC_WRITE,so it will write instead of read" is not a Windows system message.)

Edit: And I've been assuming that the fact that one line says "hnd" and the next line says "_hnd" is just a copy-n-paste error. If not, well.

Thank you for reply ,

i am using the getLastError() in this way

Code:

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#define MAPPROTWRMODE        PAGE_READWRITE

_hnd = CreateFile(fname, GENERIC_WRITE, NULL, NULL, OPEN_ALWAYS, FILE_ATTRIBUTE_NORMAL,NULL);

_hMap =CreateFileMapping(_hnd,NULL,MAPPROTWRMODE,0,_fileSize,NULL);

register int errstat=0;
 if(_hMap == NULL)
{
  errstat=GetLastError();
    if(errstat)
  printf("\n ERROR* CreateFileMapping: error=%d\n",errstat);//which  returns me 5 as number       
}

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i am using like this which gives me error=5 what does it mean ,
is it the right way i am using or any other way but does 5 indicates.

Well if you clicked around where tabstop pointed, you would get to
http://msdn.microsoft.com/en-us/libr...82(VS.85).aspx

ERROR_ACCESS_DENIED 5 0x5 Access is denied.

I still say GENERIC_WRITE should be GENERIC_READ|GENERIC_WRITE. Especially since the page that has been linked two or three times now says this:

Quote:

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Originally Posted by msdn

PAGE_READWRITE Allows views to be mapped for read-only, copy-on-write, or read/write access.

The file handle that the hFile parameter specifies must be created with the GENERIC_READ and GENERIC_WRITE access rights.

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Thank you experts thanks a lot,

thanks especially to tabstop who guessed the problem exactly, thanks to you specially,
the problem got solved , really very pleasurefull morning to me.