pointers - The meaning of "asterisk type asterisk" in C : *(volatile int *) foo -

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i have tried looking around not able find answer this. found explaining when use double asterisk, **, however, not sure whether applied case.

i have come across embedded systems code looks bit foreign me : 

port0 = *(volatile int *)(0x1c002100)

what operation doing reads gpio port address 0x1c002100. deal asterisks ?

i have written : 

port0 = *0x1c002100

are doing type of pointer type casting , hence use 2 asterisks ? best guess. thank !

look @ expression, first convert integer constant pointer, deference pointer, yield integer. same as:

int *p = (volatile int *)(0x1c002100); int n = *p; port0 = n;

the first * denotes pointer type, second dereference operator.

however second line invalid c code, since cannot dereference integer.

port0 = *0x1c002100;

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