C / C++ / MFC

Re: LNK errors while using an "extern "C"" function

10-Aug-09 18:52

You have to specify the calling convention of the exported function because the default is different in managed and native compilation.
You could declare it as __stdcall.

«_Superman_»
I love work. It gives me something to do between weekends.

MozhdehQeraati10-Aug-09 19:48

MozhdehQeraati

10-Aug-09 19:48

would you please elaborate a little bit more or send me an article with examples?
Thanks a lot

Re: LNK errors while using an "extern "C"" function

«_Superman_»10-Aug-09 19:54

Re: LNK errors while using an "extern "C"" function

10-Aug-09 19:54

The function must be declared as -
extern "C" int __stdcall foo();

«_Superman_»
I love work. It gives me something to do between weekends.

Cedric Moonen10-Aug-09 20:15

Cedric Moonen

10-Aug-09 20:15

Here[^] is a great article about calling conventions. It will help you to understand the concept.

Cédric Moonen
Software developer

Charting control [v2.0]
OpenGL game tutorial in C++

Return value from a funtion

AkashAg10-Aug-09 18:06

AkashAg

10-Aug-09 18:06

Hi,

I want to know the side effects if I don't save the value returned from a function call.

ex:

int foo()
{
   return (10);
}

main()
{
   foo();
}

Doubts:
1. Does this type of code may cause some warnings or other issues?
2. Is it an optimized approach or do I need to save the value returned by foo()?

Thanks for ur help.
Akash

«_Superman_»10-Aug-09 18:41

10-Aug-09 18:41

Ideally, you should take the returned value because there is some reason for the returning it.
Could be an error code that most people don't check. Smile | :)

As for optimization, you will have one less instruction if you don't take the return value.

«_Superman_»
I love work. It gives me something to do between weekends.

AkashAg10-Aug-09 18:46

AkashAg

10-Aug-09 18:46

yaa, true...

But if I've already checked for error conditions and all. does it matter...

«_Superman_»10-Aug-09 18:47

10-Aug-09 18:47

It really doesn't matter.
For example, I didn't know printf returned any value at all for a long time.
I believe its return value is not checked 99% of the times.

«_Superman_»
I love work. It gives me something to do between weekends.

Translate Logical Drive to Physical Drive

Stuart Dootson10-Aug-09 21:22

Stuart Dootson

10-Aug-09 21:22

akashag wrote:
1. Does this type of code may cause some warnings or other issues?

Compile it and see...neither gcc nor VC++ seem to give any warnings.

akashag wrote:
2. Is it an optimized approach or do I need to save the value returned by foo()?

You don't need to save the return value...but you then have to ask yourself - why am I calling the function? Doers it have other, non-visible side-effects? Obviously, this simple case doesn't, but many functions do effect some form of global data, while class methods can obviously update object instance data.

Java, Basic, who cares - it's all a bunch of tree-hugging hippy cr*p

Bram van Kampen10-Aug-09 14:55

Bram van Kampen

10-Aug-09 14:55

I can discover from the trusty old DOS functions on which logical drive I currently am say, drive 'C:', or drive 2. logical drive typically represents a volume on a physical drive, say '\\\\.\\PhysicalDrive0' What API's are there to translate from a locical drive identifier to the physical drive which contains the volume.

regards

Smile | :)

Re: Translate Logical Drive to Physical Drive [modified]

Randor 10-Aug-09 17:45

Randor

10-Aug-09 17:45

You could use the IOCTL_STORAGE_GET_DEVICE_NUMBER[^] control code to obtain the physical drive and volume number.

For example:

#include <Winioctl.h>
VOID LogicalToPhysical(TCHAR *szDrive)
{
	CString szPhysical;
	HANDLE h = CreateFile(szDrive, GENERIC_READ, FILE_SHARE_READ|FILE_SHARE_WRITE,NULL,OPEN_EXISTING,0,NULL);
	if(INVALID_HANDLE_VALUE != h)
	{
		STORAGE_DEVICE_NUMBER sd;
		DWORD dwRet;
		if(DeviceIoControl(h, IOCTL_STORAGE_GET_DEVICE_NUMBER, NULL, 0, &sd, sizeof(STORAGE_DEVICE_NUMBER), &dwRet, NULL))
		{
			szPhysical.Format(_T("\\\\.\\PhysicalDrive%d"), sd.DeviceNumber);
		}
		CloseHandle(h);
	}
}

//Usage:
LogicalToPhysical(_T("\\\\.\\\\C:"));

Note that this control code will fail to return correct information for mirrored and striped volumes. A more complete solution for these types of drives would be the IOCTL_VOLUME_GET_VOLUME_DISK_EXTENTS[^] control code which will return an array of partitions for the drive.

Best Wishes,
-David Delaune

Bram van Kampen11-Aug-09 11:09

Bram van Kampen

11-Aug-09 11:09

Thanks David,

Exactly the hint I Needed.

Only One Snag, Cannot find the (hex)Value of IOCTL_STORAGE_GET_DEVICE_NUMBER. Could you let me know?

Thanks and Regards,

Rose | [Rose]

Bram van Kampen

modified on Tuesday, August 11, 2009 5:17 PM

Randor 11-Aug-09 13:06

Randor

11-Aug-09 13:06

Bram van Kampen wrote:
Cannot find the (hex)Value of IOCTL_STORAGE_GET_DEVICE_NUMBER.

Interesting. They are declared in the Winioctl.h header file.

Some questions:

1.) What development environment are you using?
2.) What version of the Platform/Windows SDK are you using if any?

You can probably get away with dropping these declarations somewhere:

#define FILE_ANY_ACCESS                 0
#define FILE_SPECIAL_ACCESS    (FILE_ANY_ACCESS)
#define FILE_READ_ACCESS          ( 0x0001 )    // file & pipe
#define FILE_WRITE_ACCESS         ( 0x0002 )    // file & pipe

#define METHOD_BUFFERED                 0
#define METHOD_IN_DIRECT                1
#define METHOD_OUT_DIRECT               2
#define METHOD_NEITHER                  3

#define FILE_DEVICE_MASS_STORAGE        0x0000002d
#define IOCTL_STORAGE_BASE FILE_DEVICE_MASS_STORAGE

#define CTL_CODE( DeviceType, Function, Method, Access ) (                 \
    ((DeviceType) << 16) | ((Access) << 14) | ((Function) << 2) | (Method) \
)
#define IOCTL_STORAGE_GET_DEVICE_NUMBER       CTL_CODE(IOCTL_STORAGE_BASE, 0x0420, METHOD_BUFFERED, FILE_ANY_ACCESS)

typedef struct _STORAGE_DEVICE_NUMBER {

    //
    // The FILE_DEVICE_XXX type for this device.
    //

    DEVICE_TYPE DeviceType;

    //
    // The number of this device
    //

    DWORD       DeviceNumber;

    //
    // If the device is partitionable, the partition number of the device.
    // Otherwise -1
    //

    DWORD       PartitionNumber;
} STORAGE_DEVICE_NUMBER, *PSTORAGE_DEVICE_NUMBER;

You should really correctly setup your development environment rather than dropping the above declarations into your project. Are you using VC6 or something?

Best Wishes,
-David Delaune

Bram van Kampen12-Aug-09 8:31

Bram van Kampen

12-Aug-09 8:31

Thanks,

My version of Winioctl.h does not contain the Macro for IOCTL_STORAGE_GET_DEVICE_NUMBER, but contains all the other declarations, so, all I really needed was the Function Number (0x420). This Should (and does) work in this instance by 'dropping in', because the underlying mechanism is implemented directly by the OS and the Device Drivers, and not by a linked in compiler library.

Thanks again

regards,
Smile | :)

Bram van Kampen

Andy Belton24-Dec-11 21:37

Andy Belton

24-Dec-11 21:37

Many thanks, that solved the problem. I had looked at DeviceIoControl() but my (outdated) Winioctl.h did not have is call param!

Regards
Andy

Randor 26-Dec-11 11:13

Randor

26-Dec-11 11:13

Hey Andy,

Great to hear that it solved your problem. Yeah... I am also using old Microsoft compilers such as VC6/2005 and I have them all installed side-by-side. You should probably keep an updated 'Platform SDK'... which I believe has been renamed to 'Windows SDK'.

Somebody should probably post an article or tip that shows which SDK updates are compatible with each compiler... I am somewhat surprised that Microsoft does not have such a document. You cannot use many of the more recent 'Microsoft SDK' packages with older MS compilers. I have actually been successful with modifying some of the later SDK headers to make it work with older compilers... but that's probably not encouraged or supported.

Anyway, good luck with your project. (Why are you working the day after Christmas?) Wink | ;)

Best Wishes,
-David Delaune

Andy Belton1-Jan-12 1:40

Andy Belton

1-Jan-12 1:40

Hi David

I was a bit suprised to receive your last mail. Most people don't bother to 'follow up'.

Yes, all my stuff belongs in a museum. But, funds don't permit upgrades yet. I'm now in my 60's after over forty years in computing, single, live alone - hence working over the holidays.

A couple of questions. In your solution you gave this format "\\\\.\\\\%c:". I assume this to be for extended filepath string length support. But the documenation with my old compiler has it as "\\\\.\\"

Is this the norm for extended length support? Users are bound to come up super long path names.

Also, in my application I also access network drives. Does the "\\\\pc name\\drive name\\" give this extended length support?

Regards
Andy Belton

Randor 1-Jan-12 2:54

Randor

1-Jan-12 2:54

Hey Andy,

Andy Belton wrote:
A couple of questions. In your solution you gave this format "\\\\.\\\\%c:". I assume this to be for extended filepath string length support. But the documenation with my old compiler has it as "\\\\.\\"

Actually the documentation to your old compiler is correct... for opening the device namespace you need to prepend "\\.\" which as you know escaped looks like "\\\\.\\"

I have no idea why my old code snippit from 2009 contains an extra backslash. I write alot of these code snippits impromptu... so some of them may contain typos or minor flaws. I can tell by looking at the above code snippit that I wrote it on the spot... because it doesn't return a value... or modify any variables being passed into the function. It is just enough to illustrate the idea and help the developer move forward.

Andy Belton wrote:
Is this the norm for extended length support? Users are bound to come up super long path names.

I believe that you are referring to the Unicode version of the CreateFile Function[^]... you would need to prepend a L"\\?\" which escaped for c++ looks like L"\\\\?\\"

Andy Belton wrote:
Also, in my application I also access network drives. Does the "\\\\pc name\\drive name\\" give this extended length support?

Yes, you can access files over the network with a path greater than 260 characters however you will need to use the Unicode version of CreateFile function[^]

Best Wishes,
-David Delaune