winsock data transfer

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C++

How to pass and retrieve data in structure type from client and server using winsock2 in c++?

Posted 7-Oct-12 6:31am

Member 9404971

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Comments

aasikRaja 12-Oct-12 1:17am

could you elaborate ur qn that what data you wish to retrieve..

5 solutions

Solution 5

The simplest solution would be

if your struct is like

C++

struct MyStruct
{
int a;
int b;
};

At the sender side.

C++

MyStruct myObject;
myObject.a = 10;
myObject.b = 20;


send( SOCKET, (char*)&myObject, sizeof(MyStruct), 0);

and at recieving side;

C++

MyStruct myObjectRecv;

recv( SOCKET, (char*)&myObjectRecv, sizeof(MyStruct), 0 );

Now you can say that myObjectRecv is a clone of myObject.

Limitation of this approach is , it will produce errorneous results if your structure contains pointers.

Posted 8-Oct-12 1:02am

PrafullaVedante

Solution 1

Just send and receive as a stream of bytes. As long as both ends of the socket understand the structure of the data you should have no problems.

Posted 7-Oct-12 6:42am

Richard MacCutchan

Comments

michaelmel 7-Oct-12 20:49pm

This is partially incorrect. Explanation in my solution.

Richard MacCutchan 8-Oct-12 3:18am

Nothing incorrect about this, I have used it many times.

Member 9404971 8-Oct-12 0:05am

am sending it as the stream of bytes only.. but i couldn't get the correct data in server side...

Richard MacCutchan 8-Oct-12 3:19am

That is not an explanation of your problem. Please edit your original question and show the code you are using to send and to receive.

Solution 2

This link might be useful http://johnnie.jerrata.com/winsocktutorial/[^]

Posted 7-Oct-12 7:09am

Sergey Vystoropskiy

Solution 4

Just use a xml format.

XML

<name>MY_NAME</name>
<age>MY_AGE</age>
<address>MY_ADD
</address>

C++

char* data = "<name>MY_NAME</name><age>MY_AGE</age><address>MY_ADD</address>";
write(SOCKET_NAME,data,strlen(data));

sent it as a byte stream. and other side just parse it using a xml parser.
Here is some example of xml parser.
Using MSXML to read XML documents[^]

Posted 7-Oct-12 18:41pm

Briti Sundar

Updated 7-Oct-12 18:50pm

v2

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michaelmel · Accepted Answer · 2012-10-07T14:48:00

I understand you have asked about WinSock and C++ specifically, but still, there are some issues to consider:

Merely "understanding" the structure is insufficient. It is necessary to consider the following:

1) Data alignment. For example, if you have:

C++

typedef struct
{
 long int a;
 short b;
 long int c;
} SOME_STRUCT;

depending on compiler options, the bus width of the target CPU (e.g. 64/32/16/8 bits etc) SOME_STRUCT may end up different in size - on Windows it could be 10 or 12 bytes depending on the compiler option. This is because the compiler may leave a gap of 2 bytes after 'b' if struct members are aligned on 4-byte boundaries.

All compilers have data alignment pragmas and options. Visual studio for example, calls them "struct member alignment". So it is possible to have this different even if you use the same platform on both ends and then you could run into problems.

2) Probably not an issue unless you consider a mulitude of platforms supported by Windows CE. Then you should consider the endianness of data (as client and server may use different model). For example, client may send 4-byte integers with most significant byte first, and server may interpret them as 4-byte quantities with least significant byte first. See:

http://en.wikipedia.org/wiki/Endianness[^]

3) If you are using exactly the same platform on both ends, and you have compiled both server and client code with the same struct alignment, then you can indeed send your struct as a stream of bytes and on the other end simply interpret the received data as the same structure.

4) It is a valid and common method to define a communications protocol using C data structs provided you have specified the alignment rules and endianness of data.