Can't convert DWORD64 or double to char* to send over socket

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I am writing some code to read the free disk space as follows:

//declare the params to pass into the method to check disk usage
		ULARGE_INTEGER uliFreeBytesAvailable;
		ULARGE_INTEGER uliTotalNumberOfBytes;
		ULARGE_INTEGER uliTotalNumberOfFreeBytes;

		//init the params to pass into the method to check disk usage
		uliFreeBytesAvailable.QuadPart = 0L;
		uliTotalNumberOfBytes.QuadPart = 0L;
		uliTotalNumberOfFreeBytes.QuadPart = 0L;

		if(GetDiskFreeSpaceEx(lpDirectoryName,
			&uliFreeBytesAvailable,
			&uliTotalNumberOfBytes,
			&uliTotalNumberOfFreeBytes))

I then get the uliTotalNumberOfFreeBytes.QuadPart which is a DWORD64 and I need to send it to another application via a windows socket using the socket::send method requires the data to be sent as a char*. Please could somebody help me to convert the DWORD64 to a char*, or tell me if there is an alternative option for doing this.

I can conver the DWORD64 to a double so if someone could tell me how to convert a double to a char* that would be very helpful too :)

Posted 3-Feb-12 4:45am

Jackie Lloyd

Updated 3-Feb-12 4:48am

v2

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2 solutions

Solution 1

Hi,

If you know what you're doing you could use a static cast
(char *)TotalNumFree etc.

Make sure you got the size right when sending though (sizeof(xyz))

Cheers,

AT

Posted 3-Feb-12 4:55am

Addy Tas

Comments

Jackie Lloyd 3-Feb-12 11:07am

Hi, thanks for your suggestion, I tried this:
double dblFreeBytes
char* pCh:
pCh = static_cast<char*>(dblFreeBytes);

but the compiler message is: cannot convert from 'const char [2]' to 'int'. Have I done something wrong?

Addy Tas 3-Feb-12 11:27am

hi,

Yes You should cast the address of the double to a different size.
so pCh = (char*)&dblFreeBytes; should work

Jackie Lloyd 4-Feb-12 6:09am

many thanks - that's the same suggestion as above, which is absolutely correct and worked great :)

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Jochen Arndt · Accepted Answer · 2012-02-03T05:05:00

Solution 2

The char* parameter of socket::send is a pointer to the data memory that should be send. You can pass the address of any kind of data when using a cast:

C++

ULARGE_INTEGER val = 123;;
send(s, (char *)&val, sizeof(ULARGE_INTEGER), 0);

Posted 3-Feb-12 5:05am

Jochen Arndt

Comments

Jackie Lloyd 3-Feb-12 11:29am

Thankyou! THat worked. However, I had to convert the char* back to a double on the other side, so I used strtod() and I just get null.

char * pEnd;
double dbl;
char* val;
dbl = strtod (val,&pEnd);

Could you possibly tell me if you know what I should do to sort his out, please.

Jochen Arndt 3-Feb-12 11:34am

On the other end do it just the same way:
ULARGE_INTEGER val;
recv(s, (char *)&val, sizeof(ULARGE_INTEGER), 0);

Just treat the char* parameter as a buffer pointer. It's in your hands to what kind of data it is pointing. There is no conversion performed.

Jackie Lloyd 4-Feb-12 6:08am

Thanks everso much - it looks so easy and obvious now :)