But there is generally no reason at all to fix it at a specific address. Why do you want to?


Which illustrates why there is usually no need to fix the address at compile time!

Apart from the 'xdata' keyword extension, this is all standard 'C' - not specifically Keil


All of this is completely vanilla, plain, standard 'C' - nothing specific to Keil at all

The same end can be achieved by indexing - again, completely standard and nothing specifically to do with Keil:

To store the byte:
Buffer[index] = value;

To read the byte:
value = Buffer[index];

to increment the index to look at the next location:
index++;

To read the byte and then increment the index to look at the next location:
value = Buffer[index++];


People often say that the pointer approach is more efficient than indexing, but this is not necessarily so - it depends very much on the precise structure of your code.
As always, if this is really important to you, the only thing to do is to inspect the generated code.