C# vs C: Organizing Data Structures

Question

I want to define a data struct which I can access byte wise. In other words: I want to transfer an object of a specific data structure byte wise.

The goal is to have a high level access (access by name) to the data as well as a low level access that is only byte wise.

I do have a data transfer protocol that has a specific packet format (Header, Payload, CRC,... even bit definitions. Eventually the entire packet is 32-bit aligned).

In "C" I define a struct and access an object of this struct byte wise by casting that object into a byte array. Ie:

/* C-Code */
typedef struct
{
    int16_t a;
    int8_t b;

    /* And a bit-wise definition to make thinks really cool */
    int8_t bit_0   : 1;
    int8_t bit_1_7 : 7;

    /* (Total size is 4 bytes i.e. 32-bit aligned) */
} MY_STRUCT_t;

"my_struct" should now be read byte wise to eg transfer it to some where:
The inexpressive way:

/* C-Code */
void main(void)
{
    MY_STRUCT_t my_struct;

    for(uint32_t i = 0; i < sizeof(my_struct); i++)
    {
        Transfer_Byte( *((uint8_t *) &my_struct) + i);
    }
}

Or to make it more expressive i will define the following "union" as well:

/* C-Code */
typedef union
{
    MY_STRUCT_t data;
    uint8_t bytes[sizeof(MY_STRUCT_t)];
} MY_STRUCT_u;

and do it this way:

/* C-Code */
void main(void)
{
    MY_STRUCT_u my_struct; // object of the union this time!

    for(uint32_t i = 0; i < sizeof(my_struct); i++)
    {
        Transfer_Byte(my_struct.bytes[i]);
    }
}

Question

• How do I do this in C#? What is your suggestion? Or could you give me a hint how to solve this?

Cheers

Answer 1

For C# you're best to implement a "ToByte" and "FromByte" function and process the fields directly to ensure that the data is ordered in the manner that you wish.

BTW . I cautious using the struct union trick unless your packing and unpacking on the same platform and executable as the byte order is platform and compiler dependent for multibyte values.

Answer 2

For the Low-Level access there is a StructLayoutAttribute.Pack Field in conjunction with FieldOffsetAttribute

With these attributes you can manage how bytes are aligned in the structure.