C / C++ / MFC

10-Aug-09 19:02

I had wrote a code as follows below, is it works fine ?

<br />
void write(  char *format, ... )<br />
{<br />
va_list args;<br />
char    buffer[1025];<br />
    va_start( args, format );<br />
    vsprintf( buffer, format, args );<br />
    va_end(args);<br />
    printf( buffer );<br />
}<br />
<br />
<br />
#define txtmsg(x) write(x)<br />
<br />
int tmpval = 100;<br />
txtmsg("tempvalue = %d", tmpval );<br />

but i am not getting a correct answer

kindly help me

-kk.tvm-

Code-o-mat10-Aug-09 20:33

Code-o-mat

10-Aug-09 20:33

Depends on what it is suposed to do, really...however, you declared your txtmsg macro here:

kk.tvm wrote:
#define txtmsg(x) write(x)

to take 1 parameter (x), but here:

kk.tvm wrote:
txtmsg("tempvalue = %d", tmpval );

you used it with two ("tempvalue = %d" is one and tmpval is two), the compiler won't like that.

> The problem with computers is that they do what you tell them to do and not what you want them to do. <
> Life: great graphics, but the gameplay sux. <

kk.tvm10-Aug-09 22:24

10-Aug-09 22:24

thanks

-kk.tvm-

Adam Roderick J10-Aug-09 20:36

Adam Roderick J

10-Aug-09 20:36

Hope u want 100 to printed, right?

but in your case
u gave a wrong input to txtmsg, right?
check?
You gave it as "tempvalue = %d", tmpval to a macro,

remember, a macro never have any error checking, since it is already expanded on preprocessing time.

it will take the value for x as "tempvalue = %d", tmpval

so are getting a wrong output.

Please give correct input for your macro txtmsg like given below

int tmpval = 100;
char buff[10];
itoa( tmpval, buff, 10 );
txtmsg( buff );

Величие не Бога может быть недооценена.

kk.tvm10-Aug-09 22:26

10-Aug-09 22:26

thanks for your solution

-kk.tvm-

Stuart Dootson10-Aug-09 21:29

Stuart Dootson

10-Aug-09 21:29

You can't have variadic macros (macros with varying numbers of arguments) in C++. You can in C99, but not in standard C++.

So, change your #define to:

#define txtmsg write

and leave argument handling to the function rather than trying to do something with it in hte macro.

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

kk.tvm10-Aug-09 22:26

10-Aug-09 22:26

thanks for valuable reply

-kk.tvm-

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

David Crow11-Aug-09 3:18

David Crow

11-Aug-09 3:18

kk.tvm wrote:
I had wrote a code as follows below, is it works fine ?

Wouldn't that be your question to answer? Confused | :confused:

To solve this problem yourself, compile the code using the /P switch. Then look in the .i file to see how that txtmsg macro was expanded.

"Old age is like a bank account. You withdraw later in life what you have deposited along the way." - Unknown

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MozhdehQeraati10-Aug-09 18:43

MozhdehQeraati

10-Aug-09 18:43

I am implementing a C++.Net Class Library.(I want to use it in C#.Net later) I am using an MFC C++ header file and its corresponding lib file in that class library. I set the path for header file and lib file in the project properties. In that header file there is a class which I have no problem using it. But there is an "extern "C"" function which I have some problem with it. When I call it in my code, there are two link errors while compiling:

error LNK2028
error LNK2019

Please help me to use this function. I'd appreciate it.
Thanks in advance

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

«_Superman_»10-Aug-09 18:52

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