Hi,

Searching for the web I found this two helpful links (for Visual Studio compiler):
http://msdn2.microsoft.com/en-us/lib...65(VS.80).aspx
http://msdn2.microsoft.com/en-us/lib...y1(VS.80).aspx

The second one works for me:
Qt Code: 
  1. #pragma pack(1)
  2. struct MB_Request
  3. {
  4.    uchar function_code;
  5.    quint16 start_adr;
  6.    quint16 quantity_regs;
  7. };
  8.  
  9. #pragma pack(1)
  10. struct MBAP_Header
  11. {
  12.    quint16 transaction_id;
  13.    quint16 protocol_id;
  14.    quint16 len;
  15.    uchar unit_id;
  16. };
  17.  
  18. #pragma pack(1)
  19. struct MB_Message
  20. {
  21.    MBAP_Header mb_hdr;
  22.    MB_Request mb_req;
  23. };
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Then, executing your example code, the structs are unaligned as I need for Modbus protocol.

Could I use "#ifndef" statment to know wich compiler is used to then use "#pragma pack(1)" or "__attribute__((packed))" depending on compiler?
So when I use GCC on GNU/Linux(or windows also) it will pack the data unaligned as expected. Could use GCC with Visual Studio?

Thanks,

Thanks,