StructureToFromBuffer

C routines to convert structure elements to/from a buffer.

How it works.

All you have to do is have a C structure that represents the elements in the packed data bytes:

typedef struct
{
    uint8_t  byte1;
    uint16_t word1;
    uint8_t  byte2;
    uint16_t word2;
} MessageStruct;

Then you create a table with entries representing each element in the structure in the exact order that they will be written or read from the packed data bytes:

ElementOffsetStruct msgTable[] =
{
    // These must be in the exact order they will be in the buffer.
    ENTRY(MessageStruct, byte1),    
    ENTRY(MessageStruct, word1),    
    ENTRY(MessageStruct, byte2),    
    ENTRY(MessageStruct, word2),
    ENTRYEND
};

Writing a structure out to a buffer.

Using the populated structure variable and the matching structure entry table, all you have to do is:

MessageStruct msg;
    
msg.byte1 = 0x11;
msg.word1 = 0x2222;
msg.byte2 = 0x33;
msg.word2 = 0x4444;
    
bufferSize = StructureToBuffer (buffer, sizeof(buffer), &msg, msgTable);

bufferSize will return with the number of bytes written to the buffer, or negative if there was an error.

If successful, the buffer will contain the packed bytes of the structure:

0x11 0x22 0x22 0x33 0x44 0x44

Loading structure elements from a buffer.

Using a buffer that contains the data bytes to parse in to the structure, all you have to do is:

uint8_t data[] =
{
    0x11, 0x22, 0x22, 0x33, 0x44, 0x44, 0x44, 0x44
};

MessageStruct msg;
    
bufferSize = BufferToStructure (data, sizeof(data), &msg, msgTable);

After that, the elements of the structure will be loaded values copies from the data bytes.

bufferSize will return with the number of bytes read from the buffer, or negative is there was an error.

Errors

The header files contains #defines for the negative values that represent the following errors:

• NO_PAYLOAD_STRUCTURE (-1) - NULL check for the passed-in element table.
• NO_INPUT_BUFFER (-2) - NULL check for the source buffer (BufferToStructure).
• NO_ROOM_IN_INPUT_BUFFER (-3) - buffer too small to contain all the structure elements.
• NO_OUTPUT_BUFFER (-4) - NULL check for the output buffer (StructureToBuffer).
• NO_ROOM_IN_OUTPUT_BUFFER (-5) - not enough room for all the structure elements.