Problem with CreateFileMapping() function

**vin_pll** · 10-14-2008

Dear Experts,

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

Code:

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

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.

**Salem** · 10-14-2008

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.

**cpjust** · 10-14-2008

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.

**laserlight** · 10-14-2008

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

**vin_pll** · 10-14-2008

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:

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

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

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

**tabstop** · 10-14-2008

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.)

**vin_pll** · 10-14-2008

Dear experts,

sorry for sending that code actually it was

Code:

#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);

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

**tabstop** · 10-14-2008

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.

**vin_pll** · 10-16-2008

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.

**tabstop** · 10-16-2008

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.

**vin_pll** · 10-17-2008

Thank you for reply ,

i am using the getLastError() in this way

Code:

#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=&#37;d\n",errstat);//which  returns me 5 as number 	
}

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.

**Salem** · 10-18-2008

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.

**tabstop** · 10-18-2008

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:

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.

**vin_pll** · 10-18-2008

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.

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