Difficulty Understanding C Pointer Syntax

Question

Given the following C definitions:

#define SYNC_BYTE_1                         0x5A
#define SYNC_BYTE_2                         0xA5

and pointer declaration:

UINT8   *pCommandData;
pCommandData = GetCommandBufferPointer( LINGO_GENERAL, stringLength + 3 );

What exactly are the following two lines of code doing with the pointer?

*pCommandData++ = SYNC_BYTE_1;
*pCommandData++ = SYNC_BYTE_2;

I specifically don't understand the use of * and the ++ in this instance. If the pointer's address is being incremented shouldnt the * be replaced with a &?

Answer 1

pCommandData is a pointer to some piece of memory. The first line

*pCommandData++ = SYNC_BYTE_1;

sets the value at that address to 0x5A, and then increments the pointer pCommandData to the next address. The next line

*pCommandData++ = SYNC_BYTE_2;

works similarly: it sets the value that pCommandData points to, to 0xA5, and then increments the pointer to the next address.

Perhaps a picture would be useful. Before either line executes, the memory in the neighborhood of wherever pCommandData points to might look like this:

                    |        |
                    +--------+
pCommandData -----> |        |
                    +--------+
                    |        |
                    +--------+
                    |        |
                    +--------+
                    |        |

After *pCommandData++ = SYNC_BYTE_1;:

                    |        |
                    +--------+
pCommandData --+    |  0x5A  |
               |    +--------+
               +--> |        |
                    +--------+
                    |        |
                    +--------+
                    |        |

And after *pCommandData++ = SYNC_BYTE_2;:

                    |        |
                    +--------+
pCommandData --+    |  0x5A  |
               |    +--------+
               |    |  0xA5  |
               |    +--------+
               +--> |        |
                    +--------+
                    |        |