What is the best way to send structs containing enum values via sockets in C.
- by Axel
I've lots of different structs containing enum members that I have to transmit via TCP/IP. While the communication endpoints are on different operating systems (Windows XP and Linux) meaning different compilers (gcc 4.x.x and MSVC 2008) both program parts share the same header files with type declarations.
For performance reasons, the structures should be transmitted directly (see code sample below) without expensively serializing or streaming the members inside.
So the question is how to ensure that both compilers use the same internal memory representation for the enumeration members (i.e. both use 32-bit unsigned integers). Or if there is a better way to solve this problem...
//type and enum declaration
typedef enum
{
A = 1,
B = 2,
C = 3
} eParameter;
typedef enum
{
READY = 400,
RUNNING = 401,
BLOCKED = 402
FINISHED = 403
} eState;
#pragma pack(push,1)
typedef struct
{
eParameter mParameter;
eState mState;
int32_t miSomeValue;
uint8_t miAnotherValue;
...
} tStateMessage;
#pragma pack(pop)
//... send via socket
tStateMessage msg;
send(iSocketFD,(void*)(&msg),sizeof(tStateMessage));
//... receive message on the other side
tStateMessage msg_received;
recv(iSocketFD,(void*)(&msg_received),sizeof(tStateMessage));
Additionally...
Since both endpoints are little endian maschines, endianess is not a problem here.
And the pack #pragma solves alignment issues satisfactorily.
Thx for your answers,
Axel
