ISSUE - TCP/IP sockets in MFC VS2017

D Manivelan

Hi, I have a server client application using TCP/IP sockets in MFC VS2017. Originally i have written the code in VS2008. Kindly see the below code which sends the data to client. But this same code gives me some problem in MFC VS2017. In the below code when I assign the value 190.000015f to a local variable, its taking the value whereas when I assign it to the union member variable

UNI.S.fTestValue1

and

UNI.S.fTestValue2

it showing some junk value. Please help me to fix the problem

unsigned char* CSendValue :: SendLiveValues()
{
union USendLive
{
struct SSend
{
float fTestValue1;
float fTestValue2;
char cChr;
}S;
unsigned char Buffer[LIVEUNISIZE];
}UNI;

memset(UNI.Buffer,0,LIVEUNISIZE);

float fLocalValue;
float fTest;

fTest 		        = 190.000015f;

fLocalValue	        = fTest;   		//190.000015    // Correct value
UNI.S.cChr 	        = 'c';			//'Ô'           // Junk value - Wrong
UNI.S.fTestValue1 	= fTest;		//6.360e-39#DEN // Junk value - Wrong
UNI.S.fTestValue2 	= 190.000015f;		//1.401e-45#DEN // Junk value - Wrong

    return UNI.Buffer;

}

Richard Deeming

You have already posted this in the Managed C++/CLI forum, and been given an answer. ISSUE - TCP/IP sockets in MFC VS2017 - Managed C++/CLI Discussion Boards[^]

"These people looked deep within my soul and assigned me a number based on the order in which I joined." - Homer

Lost User

D.Manivelan wrote:

it showing some junk value.

Where is it showing, and what value?

D Manivelan

float fLocalValue;
float fTest;

fTest 		        = 190.000015f;

fLocalValue	        = fTest;   		//190.000015    //Correct value
UNI.S.cChr 	        = 'c';			//'Ô'           //Junk value - Wrong
UNI.S.fTestValue1 	= fTest;		//6.360e-39#DEN //Junk value - Wrong
UNI.S.fTestValue2 	= 190.000015f;		//1.401e-45#DEN //Junk value - Wrong

Output 190.000015 - Correct value 'Ô' - Junk value - Wrong 6.360e-39#DEN - Junk value - Wrong 1.401e-45#DEN - Junk value - Wrong

Graham Breach

This function returns a pointer to a local variable. If you want UNI.Buffer to continue to be accessible outside the function you have to allocate memory for it somehow.

Lost User

Most likely you are not converting your values to/from network order when sending and receiving. See htonf function (Windows)[^].

D Manivelan

The same code works fine in VS2008. And moreover the issue occurs when I try to initialize the union member before actually sending the data to the socket. My question is why I am not able to assign a float value to the union member which is also a float variable. This same line of code assigns the value in VS2008. Why its not doing it in VS2017

UNI.S.fTestValue1 = fTest; //6.360e-39#DEN // Junk value - Wrong
UNI.S.fTestValue2 = 190.000015f; //1.401e-45#DEN // Junk value - Wrong

Lost User

Well since we have no real idea of what your code is doing to produce these bad values, it is difficult to offer any further suggestions.

Victor Nijegorodov

Just to extend the reply of Graham Breach: move the

union USendLive
{
struct SSend
{
float fTestValue1;
float fTestValue2;
char cChr;
}S;
unsigned char Buffer[LIVEUNISIZE];
}UNI;

to the CSendValue class ctor to make the UNI a class member. Then your CSendValue :: SendLiveValues() would look like

unsigned char* CSendValue :: SendLiveValues()
{
float fLocalValue;
float fTest;

fTest 		        = 190.000015f;

fLocalValue	        = fTest;   	
UNI.S.cChr 	        = 'c';		
UNI.S.fTestValue1 	= fTest;	
UNI.S.fTestValue2 	= 190.000015f;	

    return UNI.Buffer;

}